Complete Handbook of Hydraulic Valves Technology



Hydraulic valves are crucial accessories in hydraulic systems. The valves help to control fluid flow, torque and motion of rams, plungers or pistons.

Until now, very few eBooks that focus on hydraulic valve technologies are available online. It is for such reason that a team of Saroit Engineers devote time and are willing to share over 15 years of experience in the hydraulic valves manufacturing industry.

This eBook will focus solely on hydraulic valves technology. You will learn about the: history, definition, basic principle, symbols, functions, classification, parts, troubleshooting, application and manufacturers of hydraulic valves.

It is an eye-opener for newbies and professionals in the hydraulic valves and hydraulic systems industry. The authors use simple language, illustrations and diagrams; making it easy to understand every aspect of the valves.

The eBook aims to make you comprehend and become an expert in the hydraulic valves field.

Chapter 1

Hydraulic Valve Definition

In this section, you’re going to learn about 3 hydraulic valves basics. These include:

  • Definition of hydraulic valves
  • History of hydraulic valves
  • Hydraulic valve specifications

Later in chapter two, you’ll learn about another important concept – the working principle of hydraulic valves.

For now, let’s start with:

1.1 Definition of Hydraulic Valves

Valves are mechanical fittings that direct, regulate and control the flow of fluids. They either open, close or partially obstruct the conduits.

Therefore, a hydraulic valve is a device that directs, redirects, blocks, regulates or controls the flow of fluids in hydraulic systems such as cranes, cylinders, hydraulic power packs, etc. Normally, the direction of flow will depend on the position of the spool – an important part of hydraulic valve.

You’ll learn more about hydraulic valve parts in chapter 6.

A check valve symbol, 3D representation and performance curve

Although valves are small devices in hydraulic systems, they improve performance of either industrial or mobile machinery. Their efficiency and reliability depend on the manufacturer’s innovative solutions and strict quality control (QC) processes.

You can choose from cartridge valves, directional valves, check valves, directional poppet valves, directional solenoid valves or flow valves. This will depend on the nature of the application.

You’ll learn more about the different types of hydraulic valves in chapter 5. Their design and structure will dictate how a hydraulic system works.

But, before we proceed to other sections, let’s review a brief history of hydraulic valves.

1.2 History of Hydraulic Valves

The rudimentary forms of hydraulic valves in the ancient times were stones or tree branches, which the Egyptians and Greeks could use to redirect water from rivers to irrigation schemes. With the development of the canal systems by the Romans, there was need to open, close, throttle or divert water in these irrigation systems.

Further adjustments and developments were witnessed during the Renaissance period. It was during this time that canal systems formed the intellectual basis for the development of the modern hydraulic valve systems.

An old water control valve. Image source – Valvias

The first recognizable valves in the modern history were developed during the Industrial Revolution. With the development of the first steam engines, there was need to regulate the flow of high pressure steam.

It was during this time that James Watt, begun to redesign and improve the performance of valves for the new locomotive engines and machines.

The modern valves in hydraulic power packs or other hydraulic systems have gone through series of innovations with many scientists such Fisher, Mason and Thomas (just to mention a few), making enormous contributions.

Of course, the adoption and applications of hydraulic systems in industries have contributed to the development and innovations in this industry. However, for the scope of this hydraulic valves technology eBook, I will not explore the entire history of these devices.

You can learn more by reading this: The History of Control Valves.

With these in mind, we can proceed to the next fundamental aspect of hydraulic valves:

1.3 Hydraulic Valve Specification

Basically, there are 6 main aspects you need to consider when specifying hydraulic valves for any application. This is because they determine the suitability of the valve to the hydraulic system.

An online platform for specifying hydraulic valves. Courtesy of GlobalSpec

These include:

  • Types of material

Choosing a specific type of material will depend on the nature of the application. Some of the most common types of hydraulic valve materials include stainless steel, brass, stainless steel, carbon steel, plastics, etc.

The key aspects that determine the type of material include pressure rating and operating temperature.

  • Valve type

You must specify the type of hydraulic valve for a specific application. The most common examples include cartridge/manifold, control, diverter, metering, pressure relief, solenoid, regulators, safety, spool, check, drain, needle or directional valves.

  • Size of the valve

Here, you’ll specify the size range. This will depend on the size of the piping system.

There are many industry standard valves, however, you may also opt for custom made valves. You have to specify the nominal size of the valve and required tolerances.

  • Pressure rating

Your valve will only handle a specific amount of pressure. Therefore, depending on the hydraulic system, you should be able to choose a valve with an appropriate pressure rating.

  • The number of ways/ports

Valves come with many ports depending on the specific application requirements. You can choose:

  1. 2 ways solenoid valve – it has 1 port inlet and 1 port outlet.
  2. 3 ways solenoid valve – there are 3 different options which include 1 port inlet, 1 port outlet and 1 port exhaust; 1 port inlet and 2 ports outlet; 2 ports inlet and 1 port outlet.

In short, this specification will depend on your hydraulic system. Don’t worry, you’re going to explore this further in chapter 5.

  • Actuation mechanism

This is basically the mechanism that causes the valve to either close or open in response to fluid flow. Some of the main common mechanisms include mechanical devices, electro-hydraulic, pilot operated, electric, manual or thermally actuated.

Moreover, you need to know how these hydraulic valves work, the maintenance process, installation procedure and troubleshooting. You’ll learn about all these shortly.

For now, let’s proceed to chapter 2 that focuses on the working principle of hydraulic valves.

Chapter 2

Hydraulic Valve Working Principle

In this section, you’ll learn about the working principle of hydraulic valves. The process may vary slightly depending on the design and structure of the valves.

This chapter will act as an introductory phase since we may not explore how all types of hydraulic valves work in totality. You will learn more about this in chapter 5.

For a fact, different valves have unique parts and designs leading to a slight variation in their working principle. Take for instance, the valve actuating mechanisms.

This section of the hydraulic valves technology eBook will mainly focus on the working principle of the directional control valves. It illustrates all the basic working principles of hydraulic valves.

First, you can watch this video on how a directional control valve work, courtesy of LunchBox Sessions.

As you’ve seen in the video above, the idea here is to ensure that the valve opens and closes thereby, directing fluid to the desired direction. This is possible through a number of actions and processes.

2.1 The Working Principle of Directional Control Valves

Directional hydraulic valves play an integral role in hydraulic systems. As illustrated in the video above, I will explain this in this section before we explore a special type of directional valve called hydraulic cartridge valve.

In any hydraulic system, the position of the valve keeps on changing depending on the desired direction of the fluid in the pipeline. This is quite evident in the valve symbols below:

A hydraulic directional control valve. Image source – Design Aerospace LLC.

Don’t worry, you’ll learn more about hydraulic valve symbols in chapter 3.

As I had indicated in chapter 1, these valves are either 2-way, 3-way or 4-way. The number of ways and positions of hydraulic valves will depend on the complexity of the hydraulic system.

As I had indicated in chapter 1, these valves are either 2-way, 3-way or 4-way. The number of ways and positions of hydraulic valves will depend on the complexity of the hydraulic system.

What make the working of principle of hydraulic valves somehow complicated is the valve actuation mechanism. Normally, operators can switch the position of the valve by hand, hydraulic pilot or electrical solenoid (you’ll learn about their principle of operation shortly).

Alternatively, other hydraulic valves are spring loaded. That is, the spring returns them back to their original position/full back condition.

At the same time, some valves are held in the same position until they are reset.

The figure above shows various parts of a directional control valve with the following key features: 1 – body, 2 – spool, 3 – solenoid, 4 – return spring. Image source – ResearchGate

In short, these valves perform a number of functions through a simple mechanism – changing the position of spool. This causes the valve to stop, allow or change direction of fluid flow.

The valve spool, as you will learn in Chapter 6, plays an integral role in hydraulic systems. A valve may have a rotary or sliding spool.

Now, let’s review some of the hydraulic valves actuating methods. These are critical aspects that determine the working principle of hydraulic valve systems.

2.2 Working Principle of Manually Operated Hydraulic Valve

They use pedals or levers, where the operator applies a predetermined amount of force to open and close the valve. Other valves use spring to return the valve to its original position.

How a Mechanically Operated Hydraulic Valve Works

In these hydraulic systems, the mechanical components such as rollers, wheels or cams provide the required force that moves the valve. Quite a number of mechanically operated valves are prone to wear.

Working Principle of Solenoid Operated Hydraulic Valves

These hydraulic systems use electro mechanical solenoids that slide the spool to the right direction. They are common in most hydraulic systems because a small electrical energy precisely controls the position of the valve spool.

A pilot operated hydraulic control valve. Image source – Hydraulics Pneumatics

Although they are efficient, these valves have the following main challenges:

  • Electrical energy may not generate large forces
  • It dissipates heat
  • Limited duty cycle

The solenoid operated hydraulic valves are suitable for pilot valves (small hydraulic valves).

With this knowledge, we now explore the working principle of another special type of hydraulic valve; the hydraulic cartridge valve. This is a common equipment in most hydraulic power packs.

The Working Principle of Hydraulic Cartridge Valves

A hydraulic cartridge valve is an important accessory in the hydraulic systems. They are intelligent, compact in designs and cost-effective.

Three different types of hydraulic cartridge valves

Quite a number of hydraulic cartridge valves are pilot operated check valves. They have an equal area on both ports.

Their key sections include sleeve, valve poppet/cone and closing spring. Normally, as the hydraulic fluid flows into the system via the port, it pushes the poppet to open.

A light-weight spring holds the poppet in place during a shutdown process, however, it can be overpowered, allowing fluid transfer. Depending on the controller input, you can use hydraulic cartridge valves for directional control, pressure control, check and flow control valves.

All these make hydraulic cartridge valves a perfect choice for a wide range of applications in the hydraulic systems. Again, such valves are mainly mounted in the hydraulic manifold block.

An example of hydraulic cartridge valve manifold

To achieve any of the above functionalities, the valves are connected either in series or parallel. Moreover, the hydraulic cartridge valve may include other singular function valves.

These results in a single system that is easy to control and improve the efficiency of the system.

With this knowledge I am sure you now know the working principle of hydraulic valves. You’ll learn more about this as we will be discussing the various types of hydraulic valves.

Before that, it is prudent to know the various symbols of hydraulic valves. Normally, in hydraulic circuits, we use the symbols as opposed to the pictorial or 3D image.

Therefore, the chapter 3 of this hydraulic valve technology eBook is a guide that will help you interpret the various valve symbols in any engineering drawing. It is a vital section for both professionals and newbies in the hydraulic systems industry.

Chapter 3

Hydraulic Valve Working Principle

In engineering or technical drawings, we use symbols to represent real components. It is the same case in hydraulic circuit drawings like in the figure below:

A sample of hydraulic circuit with symbols. Image source – Hydraulics & Pneumatics

Without a clear understanding of hydraulic circuit symbols, you cannot interpret information represented in the above diagram. That is, it will be impossible to implement the hydraulic circuit in any practical application.

For the scope of this eBook, we will focus on hydraulic valve symbols. However, in case you need to learn more about hydraulic circuit symbols, you can read this: ISO Symbols in Hydraulics & Pneumatics.

3.1 Types of Hydraulic Valve Symbols

In this section, you will learn about 8 different categories of hydraulic valve symbols and they include:

  • Directional control valve symbols
  • Check valve symbols
  • Shuttle valve symbols
  • Rapid exhaust valve symbols
  • Pressure control valves symbols
  • Flow control valves symbols
  • Shut-off valve symbol

Basically, these are all the possible combinations of valves in hydraulic circuits. By the end of this chapter, you should be able to interpret and identify the valves in any technical drawing.

Later in chapter 4, you’re going to learn about the various functions of each hydraulic valve.

So, let’s start with the:

Directional Control Valve Symbols

There are many types of directional control valves depending on their specific functions. As you will see shortly, directional control valves are represented using square boxes.

Each of these square boxes represent the valves position. That is, they represent the number of valve operating positions.

This implies, a directional control valve with 3 boxes; represents 3 operating positions while 4 boxes represents 4 operating positions. Normally, the arrows in the box show the direction of flow in the pipe system.

For a fact, there are many types of directional control valves with varying number of ports and positions. Below are hydraulic valves schematic representations:

A 4-way, 3 position directional control valve. Image source – Design Aerospace LLC.

NOTE: The image to the left shows a symbol of a 4-way, 3-position directional control valve symbol. However, on the right we have the actual valve with a spool.

A 4-way, 2-position directional control valve. Image source – Design Aerospace LLC.

A 2-way, 2-positions directional control valve. Image source – Design Aerospace LLC.

Do you see and difference in the three types of directional control valves above. Well, I believe is quite clear.

So, it is important to note that the directional control valve symbols vary in design depending on the number of ways and positions.

But, how does the number of ways and positions. affect the working principle of directional control valves? What makes these significant features?

Basic Facts about Directional Control Valve Symbols

Let’s make a few facts clear since this knowledge is fundamental when choosing an appropriate hydraulic valve for a specific application. Remember, I had mentioned that the basic symbol of a valve is square box/envelope.

This is what I mean:

A representation of a directional control valve. The number of boxes vary depending on the type and design of the valve (ideally, the number of boxes refer to number of positions of the valve)

You should understand these two aspects:

  • Number of “Positions” in Directional Control Valves

This refers to the number of switching positions when the valve is in use. That is, the specific direction the hydraulic fluid will flow on shifting the valve.

It is represented by the number of square boxes/envelopes. For instance, the diagram above is for a 3 position valve.

Therefore, a 4-way, 2-position directional control valve implies that the valve has only two switched positions.

Ideally, this refers to the number of positions the spool will take. They may be 2, 3 or 4 positions depending on the hydraulic valve design.

  • Number of “Ways” in Directional Control Valves

In directional control valves, the word “ways” refers to the number of ports in the valve. For example, in a 4-way, 2-position valve; the “4-way” implies that the valve has 4 ports/pipe systems connected to it.

These pipes may include port A, port B, pressure and return. This is quite evident in the above hydraulic valve symbols.

Ideally, this also refers to the total number of directions a hydraulic fluid can flow through the valve. Again, of essence is that in most cases, the number of ways determine the applications of the valve.

That implies:

Type of ValveCommon Applications/Uses
2-Way ValveON/OFF fluid supply applications
3-Way ValveUnidirectional motors and single acting cylinders
4-Way ValveBi-directional motors and double acting cylinders
5-Way ValvePneumatic systems equipped with dual air pressure

Now, at this point, you should be able to:

  1. Identify directional hydraulic valves in hydraulic circuits
  2. Describe their applications
  3. Choose appropriate valve for an applications

Apart from these, let’s explore other hydraulic valve symbols.

Check Valve Symbols

In hydraulic systems, check valves only allow for flow in one direction. Their construction feature a poppet and spring.

Most check valves are pilot operated. Below is a hydraulic circuit with a symbol of a check valve.

A check valve in a hydraulic circuit. Image source – Design Aerospace LLC.

Shuttle Valve Symbol

The hydraulic shuttle valves are common in pneumatic systems thou you may use them in hydraulic systems. They allow fluid to flow through them from two sources.

A shuttle valve

Rapid Exhaust Valve Symbol

Rapid exhaust valves play a fundamental role in emergency situations. These may include situations where you wish to release compressed air into the system or perform and emergency stop.

A rapid Exhaust Valve. Image source – Engineering Student

Pressure Control Valve Symbols

There are many types of pressure control valves. Each valve perform a unique function, aiming to optimize all operations of hydraulic systems.

Here, you’re going to learn about 4 different types of pressure control valves symbols:

  • Pressure relief valve symbol

Pressure relief valve (PVR), which is also called safety valve, limits pressure build up in hydraulic circuits. That is, it allows pressurized hydraulic fluid to flow through an auxiliary passage.

Pressure relief valve

  • Proportional pressure relief valve symbol

In these proportional pressure relief valves, the pressure in the hydraulic fluid is maintained at pre-set value. This pressure is proportional to an electronic signal.

A Proportional pressure relief valve symbol

  • Sequence valve symbol

Quite a number of sequence valves are pilot operated. The working principle is such that the hydraulic fluid only flows to the second port after it reaches a present value of the valve.

A Sequence valve symbol

  • Pressure reducing valve symbol

In hydraulic circuits, pressure reducing valves limit the overall pressure to a certain limit. The valve is common in downstream piping systems.

Pressure reducing valves symbol

Flow Control Valves symbols

There are many types of flow control valves that have been modified to suit the specific requirements of a hydraulic application. Below are 10 different types of flow control valve symbols you need to know:

Shut-off Valve Symbol

A shut-off valve is represented as:

In short, these are the hydraulic valve symbols you’ll find in any technical drawing or circuit representation.

With all these in mind, now we can proceed to the next section of this hydraulic valve technology – functions of hydraulic valves in chapter 4.

Chapter 4

Hydraulic Valve Function You Should Know

In chapter 3, you did learn about some applications of hydraulic valves. This chapter focuses mainly on practical functions of hydraulic valves, which may vary depending on the valve structure and design.

With a suitable valve, you can direct hydraulic fluid safety to optimize operations in the hydraulic systems.

To make it easy and simple for you to understand, this section will focus on the main functions of four main types of hydraulic valves. These include:

  • Directional control valves
  • Flow control valves
  • Pressure control valves
  • Check and shuttle valves

As you will learn in chapter 5, these valves can further be divided into different sub-categories. The chapter will cover over 15 different types of hydraulic valves.

With that, I am sure you can definitely choose the right valve for your applications. For now, let’s have an overview about the specific functions of hydraulic valves

4.1 Functions of Hydraulic Directional Control Valves

Hydraulic directional control valves are important control elements in the hydraulic systems. By knowing the specific functions of these valves, you can easily select appropriate mechanisms to improve fluid power in any application.

As the names suggest, the main function of a hydraulic directional control valve is to control the direction of the hydraulic fluid. It does this by changing the position of the movable parts within the valve system.

You can see this as illustrated in the video below:

In any fluid power system, a hydraulic directional control valve will perform the following key functions:

  • Isolate specific pipes or branches of a hydraulic circuit.
  • Help change direction, start, accelerate, stop or decelerate motion in hydraulic actuators.
  • It vents the relief valve either through mechanical or electrical control
  • Allow free flow from the pump to the reservoir. This occurs at low pressure where the pump delivery is not needed in the system.

Basically, these are simple forms of switching mechanisms (on/off switching) that control the movement of hydraulic actuators.

A good example is the 4-way directional control valve that is commonly used in industrial hydraulic systems.

Remember, the switching configuration will depend on the specific application of the valve.

4.2 Functions of Hydraulic Flow Control Valves

The complexity of a hydraulic control valve will depend on its specific functions. Therefore, a hydraulic system may have many actuators that should operate at different speeds.

Different types of flow control valve. Image source – E4Training

In such situations, you will require a hydraulic flow control valve. These valves control the speed of actuators allowing for varying degree of movements.

That is, the hydraulic flow control valves allow changes to be made either during the operation or setup. They can increase or decrease the opening of the throttle, thereby determining the movement of hydraulic actuators.

4.3 Functions of Hydraulic Pressure Control Valves

Hydraulic pressure control valves may have a throttle or fixed throttle. Some of the key functions of pressure control valves include:

  • Maintaining a maximum pressure to a certain preset level
  • Determined the level of work pressure
  • Unloading hydraulic pump
  • Regulating level of pressure

Pressure control valve. Image source – Hydraulics & Pneumatics

Remember, excess pressure in the hydraulic systems may cause pipes to burst or failure of other hydraulic systems. On the other hand, low pressure may cause failure in a hydraulic system.

Therefore, hydraulic pressure control valves help maintain the system pressure to a suitable level.

4.4 Functions Hydraulic Check and Shuttle Valves

Hydraulic check valves are important accessories in hydraulic systems.

This is due to the following key functions:

  • Installing them on the return lines prevent hydraulic fluid from draining out of the reservoir during maintenance
  • At times, you can use them as low pressure relief valves. However, you should note that these valves do not have a superior pressure rise rate.
  • They are used for load holding. That is, after switching off the power supply or directional control valve, they will hold the load in position i.e. locking the cylinder in position.
  • Can work as directional control valves, especially when low leakage is required.
  • May provide positive feedback in hydraulic systems

NOTE: Some of these applications may require that the valve be modified appropriately.

Check and shuttle valves

Broadly, these are the main categories of hydraulic valve. As you may have noticed in this chapter, the functions of a hydraulic valve mainly revolve around three key aspects:

  • Direct the flow of fluid in hydraulic system
  • Control the volume of hydraulic fluid
  • Regulate the pressure in hydraulic system

You will learn more about these as we discuss the individual hydraulic valve types in our next Chapter of this hydraulic valves eBook.

Chapter 5

Hydraulic Valve Types

In this section, you will learn about the various sub-categories of valves. This will give you an in-depth knowledge on what has been mentioned previously in chapters 3 and 4.

So, chapter 5 will focus mainly on the sub-categories of:

  • Pressure control hydraulic valves
  • Flow control hydraulic valves
  • Directional control hydraulic valves

The main areas of focus will be the key applications and features of each sub-category. Moreover, it will also include either a video or image of every hydraulic valve.

With this, you’ll be able to choose the right valve for a specific application. The section will cover over 20 different types of hydraulic valves.

Now, let’s start with the:

5.1 Pressure Control Hydraulic Valve

As you can see, these are broad functions. With this information alone, it is nearly impossible to choose the right pressure control valve for a hydraulic system.

For sure, this can be a nightmare if you’re new to hydraulic systems. Therefore, in this section, you will learn about these 7 different types of pressure control valves:

  • 5.1.1 Hydraulic relief valve
  • 5.1.2 Pilot operated hydraulic relief valve
  • 5.1.3 Spool type hydraulic relief valve
  • 5.1.4 Hydraulic pressure reducing valve
  • 5.1.5 Hydraulic sequence valve
  • 5.1.6 Hydraulic load control valve
  • 5.1.7 Hydraulic counterbalance valve

Remember, these are pressure control valves. They come in unique designs suitable for specific applications.

Let’s review each of these pressure control valves:

5.1.1 Hydraulic Relief Valve

Hydraulic relief valves play an integral role in hydraulic systems. They are the most commonly used pressure control valves.

In hydraulic systems, you can use these valves mainly for two major roles:

  • Protect hydraulic circuits from overload
  • Limit force or toque from rotary motors or linear actuators

These functions may vary depending on the design of a hydraulic system. However, this does not imply that the relief valves will have a completely unique design.

The internal design of all these valves is basically the same. Broadly, hydraulic valves have two sections.

These include a piston that is normally retained by springs and a pilot-valve or cover that controls the piston’s movement.

Normally, you can adjust the control range using screws.

This is an image of hydraulic relief valve. Image source: Hydraulic Valve.

To ensure that these relief valves remain effective in hydraulic systems, it is advisable to adopt an appropriate cleaning process. That is, you should reduce the operating pressure since this will help flush out any possible sludge deposits.

This implies that, operating hydraulic relief valves at reduced pressure removes sludge deposits.

In most cases, the complexity of relief valves in a hydraulic circuit will depend on the specific functions you intend to achieve. Still, the working principle will still remain the same.

Here is what you should expect:

You can connect a relief valve in a hydraulic system such that one port is in line with pressure line while the other port is connected to a reservoir. The ball will remain in position and this will be due to a force exerted on it by the spring.

You can change this by adjusting the hydraulic relief valve’s screw.

As the hydraulic system operates, the hydraulic relief valve will remain closed as long as the pressure remains below the minimum threshold to overcome the force exerted by the spring.

Whenever the pressure at the inlet exceeds the force exerted by the spring, the ball moves from its position. This opens the valve and the hydraulic fluid flows through the pressure line to the reservoir.

Normally, this diversion prevents increase in pressure in the hydraulic system. As the pressure at the inlets reset back to the initial value, the valve will close again.

You should note these key aspects here:

  1. Cracking pressure: This is the pressure at which the hydraulic relief valve begins to function.
  2. Full-flow pressure: It is the pressure at which the valve allows maximum fluid to pass through.

In short, before you choose this valve, it is important to understand the hydraulic fluid circuit structure and its function.

5.1.2 Pilot Operated Hydraulic Relief Valve

Under normal circumstances, you may have to choose between a direct acting valve and pilot-operated valves. But, what brings the difference?

A pilot operated valve mainly regulates the pressure. On the other hand, a direct-acting valve will prevent over pressure.

The way these two valves operate, may depend on their design. For now, let’s focus on pilot operated hydraulic valves.

Below is a video showing how a pilot operated relief valve works:

The pilot operated hydraulic valve designs are such that they may regulate pressure based on two distinct factors:

  • Use internal pressure setting to control pressure
  • Depend on a remote circuit to regulate pressure

In most cases, they are a perfect choice in situations where multiple settings are required to control hydraulic fluid.

Normally, you can use a pilot operated hydraulic relief valve to unload the pump at low pressure. This practice is common in periods between work cycles.

5.1.3 Spool Type Hydraulic Relief Valve

These hydraulic relief valves have a spool located in their housing. Normally, there must be an actuation force to control the spool.

Spool type hydraulic relief valves have unique features such as:

  • High switching power
  • Low actuating force
  • Robust control function

The working principle here is not different from that of the directional spool valves. Below is an example of spool type hydraulic relief valve:

This an example of a water hydraulic relief valve with a spool. Image source: The American Society of Mechanical Engineers.

In most cases, the spool type valves unload flow after the hydraulic system reaches a required pressure setting. The design of the spool type hydraulic valves guarantees a fast responding and reliable performance.

Whenever you are using a spool type hydraulic valve, it is important to take care of any possible leakages. You will find that operating a spool type hydraulic relief valve at high pressure may result in leakage losses.

The leakages are common around the spool. They depend on the following key aspects:

  • Gap between the spool and the hydraulic relief valve housing
  • Hydraulic system pressure
  • Viscosity of the hydraulic fluid

In short, a good understanding of a hydraulic system will help you to choose the right spool type hydraulic relief valve.

5.1.4 Hydraulic Pressure Reducing Valve

A hydraulic pressure reducing valve is yet another important accessory in hydraulic systems. It makes redesigning the existing hydraulic systems cost competitive.

In hydraulic circuits, these valves limit pressure in brand circuits. At times, the average pressure in the main hydraulic system can be 750 psi, and the maximum pressure requirement in one of the branch-circuits is 250 psi.

This is a hydraulic pressure reducing valve. Image source: Valve Hydraulic.

In such situations, you will need a hydraulic pressure reducing valve in the system and it must be set to 250 psi. Like in other hydraulic valves discussed earlier, the valve will remain open as long as the pressure is not sufficient to overcome the force of the spring.

Otherwise, the valve will close partially or fully, depending on the amount of pressure.

5.1.5 Hydraulic Sequence Valve

These valves play an integral role in a sequence of operations in hydraulic circuits. That is, one action cannot take place before the other.

Definitely, all these actions must be related. Take for example, the landing gears of an aircraft.

The process is such that, the landing gear only begins to extend after the landing gear doors are fully open. Furthermore, the door only closes after the landing gears have fully retracted.

Here is a video illustrating how hydraulic sequence valves work in fork lifts:

So, what makes hydraulic sequencing valves different from the other types of hydraulic relief valves?

Ideally, the working principle of sequence valves is similar to that of the relief valves. However, in the case of hydraulic sequence valves, after reaching the set pressure, it diverts the fluid to the next actuator to perform other tasks within the system.

You can learn more about hydraulic sequencing circuits by watching this video:

The sequence valves come in a wide range of shapes and designs. For instance, when it comes to hydraulic systems, you can choose either a mechanical or pressure control sequence valve.

It is important that you understand the order in which every operation should take place.

5.1.6 Hydraulic Load Control Valve

The load control valves play an integral role in the hydraulic systems. They come in a wide range of shapes and designs.

Hydraulic load control valves are mainly designed to prevent the load from running ahead of the hydraulic pump. That is, hydraulic load control valves provide a positive load holding.

Basically, they are special types of hydraulic pressure valves that prevent loads on either motors or cylinders from dropping in an uncontrollable manner.

They are common in both positioning, and moving systems. Some of the most common designs may include screw-in cartridge or inline housing valves.

This is a hydraulic load control system. Image source: Hydraulics and Pneumatics.

Depending on the intended application, you may go for the following types of hydraulic load control valves:

  • Pilot vented or assisted load control valves
  • Manifold mounted motor control valves
  • Counter balance valves
  • Load control valve cartridge

In short, there are many series depending on the specific hydraulic system requirements. At times, hydraulic valve manufacturers may decide to combine different functionalities into one valve.

That is, you may find a valve with three different functions such as: Pipe-rapture safety protection, safety valve and load control.

So, before you purchase a hydraulic load control valves, know all possible functionalities and specifications.

5.1.7 Hydraulic Counterbalance Valve

In hydraulic systems, you’ll find counter balance valves in applications that work with either suspended or overriding loads. The hydraulic counterbalance valves create a back pressure to prevent any possibility of losing control over the load.

They are designed such that they allow free flow in one direction and prevent flow of hydraulic fluid in another direction until a certain system pressure is reached.

These are two different designs of counterbalance valve.

The hydraulic counterbalance valves are also called the load holding valves. They are designed such that they can control the motion of the load in the following ways:

  • In case of tube or hose failure, they prevent load from dropping
  • Prevent the load from drift whenever there is a leakage in the spool of directional control valves.

The hydraulic counterbalance circuits come in a wide range of designs. This depends on the complexity of the hydraulic circuit and the specific tasks it should handle.

At this juncture, I am sure you can clearly distinguish the various pressure control valves available. As you may have realized, some of these valves may perform the same function in hydraulic system when modified accordingly.

Apart from these, another set of valves that play an important role in hydraulic systems are the flow control hydraulic valves. You will learn more about them in the next section of this hydraulic valve eBook.

5.2 Flow Control Hydraulic Valve

The flow control hydraulic valves regulate flow rate of hydraulic systems. As a result, you can perform the following key functions easily:

  • Control the speed of an actuator
  • Regulate rate of energy transfer in the hydraulic system

Ideally, a hydraulic flow control valve acts as a “fluid switch”.

These flow control hydraulic valves come in a wide range of designs and shapes, for various applications.

Some of the key applications may include material processing, conveyor systems, manufacturing, transport industries, etc.

Normally, a high quality flow control hydraulic valve is regarded as one that guarantee consistent flow irrespective of the load. That is, they can effectively limit the amount of fluid flow in hydraulic circuits.

Furthermore, a high quality flow control valve should reduce the effect temperature. This will also depend on the nature of the hydraulic valve design.

Furthermore, a high quality flow control valve should reduce the effect temperature. This will also depend on the nature of the hydraulic valve design.

By the end of this section, you should be able to choose an appropriate flow control valve for your application.

So, let’s start with:

5.2.1 Hydraulic Needle Valve

Hydraulic needle valves are valves with a needle-shaped plunger or long tapered point on one end of their stem. These are unique valves that are common in hydraulic systems with relatively low flow rates.

Due to their unique design and how they control fluid flow, you can use them as throttle valves. Ideally, these valves are suitable when controlling fluid flow in delicate components in a hydraulic system.

Below, is a video showing how hydraulic needle valves work:

As you can see in the video, a tapered pin gradually opens and closes the conduit. This allows for fine and smooth flow of the hydraulic fluid.

Clearly, by turning the screw, you can comfortably regulate the fluid flow using a hydraulic needle valve.

But, where exactly can you use a hydraulic needle valve?

Needle valves are suitable for the following key applications:

  • Control flow into delicate gauges; such components that may get damaged by a sudden surge in fluid pressure.
  • Ending working cycle; a hydraulic system can slowly be stopped by adjusting the needle valve
  • Common in metering applications
  • Bleed valves in heating applications

Although a number of hydraulic valve manufacturers are trying to adopt other mechanisms of opening and closing these valves, most of them are manually operated.

Apart from the hydraulic needle valve, another essential valve is the:

5.2.2 Hydraulic Flow Divider

A hydraulic flow divider is a key component of a flow divider cartridge. They are available in different designs and configurations.

Depending on the nature of the application, you may use this hydraulic valve as a hydraulic flow divider or hydraulic combiner. Generally, you can represent hydraulic valve divider as:

This is a simple circuit of hydraulic divider valve circuit. Image source: Hydraulic & Pneumatics

Depending on the nature of the flow control requirements, you may opt for divider valves with varying pressures and flow rates. Furthermore, the complexity and dynamisms in the hydraulic circuits have led to the design of more efficient valves.

Examples of hydraulic applications where these valves play a critical role include: Flow partitioning, cylinder synchronization, transmission differentials and motor synchronization. Normally, advanced hydraulic flow divider valves have interlocking spools that help in pressure compensation.

Such hydraulic flow divider valves have a complex circuit diagram. Here is a good example:

Spool-type hydraulic flow divider valves

As you can see from the images above, the hydraulic fluid that passes through the valves splits into two. Moreover, from the circuit diagram above, you can easily tell the direction of hydraulic fluid flow.

In most cases, a spool type hydraulic flow divider valve does not allow for reverse flow. It is for this reason that spool type hydraulic divider valves used to synchronize cylinders features a check valve.

The check valves pass the reverse flow.

Apart from the hydraulic flow divider/combiner valve, another essential valve is the pressure compensated flow control valve.

5.2.3 Pressure Compensated Flow Control Valve

Are you operating a hydraulic system that requires constant flow with varying pressures and loads? Well, the modern pressure compensated flow control valves feature unmatched features such as:

  • Almost no change flow with pressure variation
  • Durable with reverse pressure function
  • Tamperproof options

This makes pressure compensated flow control valves suitable for hydraulic power packs/units, accumulator bleed-off and motor/cylinder speed control.

Below is a diagram showing a pressure compensated flow control valve:

This is an image of pressure compensated flow control valves. Image source: Valve Hydraulic

So far, you’ve learned about flow control valves; but what makes pressure compensation an important aspect here?

The pressure compensated flow control valves feature a setting that allows for safe variations in pressure in the hydraulic system. This hydraulic valve eliminates undesired change in actuator speed with any change in load.

In short, the pressure compensated flow control valves are suitable in applications where hydraulic actuators should maintain a constant speed irrespective of any change in load or pressure.

5.3 Directional Control Hydraulic Valve

Directional control hydraulic valves are versatile components of hydraulic systems. They are uniquely designed to: Change direction, stop and allow hydraulic fluid flow.

Depending on the type of hydraulic circuits, they are available in simple designs such as the 2-way valve to those with complex structure such as the 4-way control valves in the double-acting actuators.

A directional hydraulic control valve

The directional hydraulic valves may have sophisticated control mechanisms that enhance performance and functionality. These may include either manually or solenoid controlled directional control valves.

Ideally, with the advancement in technology, you can adapt directional control valves to nearly any application. For instance, you may opt for poppet type, sliding spool or screw-in cartridge valves; just to mention a few.

The unique designs of these valves aim to reduce leakage in the hydraulic system while preventing load drop.

Below are different types of directional hydraulic valves you need to know:

5.3.1 Hydraulic Solenoid On/Off Valve

Hydraulic solenoid On/Off valve is an electromechanically controlled valve. They are controlled by an electric current that passes through the solenoid.

Solenoid valves are used in many applications such as hydraulic manifolds to achieve the desired performance.

These are a series of solenoid valves. Image source: Wikipedia

In certain hydraulic fluid applications, you may use a solenoid operated On/Off hydraulic valves. However, you need to deal with certain problems such as hysteresis and saturation.

The hydraulic solenoid On/Off valves are available in a wide range of shapes and designs where the solenoid may be activated by a pressure switch, electrical On/Off device or level probe.

For solenoid pilot valves, there is an option for manual operation.

5.3.2 Hydraulic Spool Valve

As you have learnt in the previous sections, there are many types of hydraulic valves. They come in a wide range of shapes and designs.

A good example is a hydraulic spool valve. In these valves, the position of the spool determines the direction where the oil will flow.

Some examples of hydraulic spool valves include:

  • ON/OFF directional spool valves
  • Proportional spool valve
  • Valve combinations

The directional spool valves, are popular for low actuating force, a range of control functions and high switching power. Normally, the spool within the valve housing either connects or separates depending on the available actuating force.

This is an example of a directional spool valve. Image source: Valve University

For the scope of this section, we’ll discuss the following three types of spool valves:

  • 3W2P hydraulic spool valve
  • 4W2P hydraulic spool valve
  • 4W3P hydraulic spool valve

So, let’s start with: 3W2P Hydraulic Spool Valves

A 3 way spool type solenoid valve is common in most hydraulic applications. Normally, you’ll find valves with a wide range of flow rates and pressures.

All these depend on specific designs of the 3 way valve. Can you remember how a 3 way 2 position directional control valve works?

I had discussed this earlier in this hydraulic valve eBook.

This is a complete diagram showing the working principle of 3W2P hydraulic valve. Image source: MathWorks

The only difference here is the hydraulic valve spool. You’ll learn more about the hydraulic valve parts in chapter 6 of this hydraulic valve eBook.

Under normal circumstances, the 3W 2P hydraulic spool valve designs ensure predictable and reliable performance even in minimal hysteresis or low pressure drop. This makes these 3 way 2 position valves a perfect choice for unloading or switching applications that do not require low poppet leakage.

Closely related to this is the: 4W2P Hydraulic Spool Valves

A 4 way 2 position hydraulic spool valve equipped with a solenoid offers a perfect and effective fluid flow control mechanism. They are suitable for both either actuation or reversing applications.

Depending on their structural design, you can use these valves for a range of flow rates and pressures.

This is a schematic drawing of a 4 way 2 position hydraulic valve.

The working principle of the 4W2P hydraulic spool valve is quite similar to those I had discussed earlier in this eBook. 4W3P Hydraulic Spool Valves

In case you have forgotten how a 4 way 3 position hydraulic valve works, here is a practical video of the same:

The 4W3P hydraulic spool valves are common in a number of complex hydraulic systems such as reverse flow control, actuator applications, pilot circuits and bi-directional motors, just to mention a few.

The working principle and specification is not different from the two hydraulic spool valves I have discussed above.

Now, at this juncture, all that remains is your ability to understand the basic parts of hydraulic valves and their respective functions. You will learn about this in chapter 5.

But before that, let’s have a quick overview of another critical component of the hydraulic circuit; the hydraulic check valve.

5.3.3 Hydraulic Check Valve

Hydraulic check valve is a simple and essential type of directional control valve. The design of these check valves is such that they allow hydraulic fluid to flow in one direction and stop flow in the opposite direction.

At times, they are also referred to as non-return valves. In most hydraulic fluid systems, they:

  • Protect hydraulic systems from pressure surges
  • Act as bypass or prefill valves
  • May work as pre-tensioning valves

The available hydraulic valves are available in a range of designs and shapes. In most cases, these valves are spring-loaded with either a plate or a ball that prevents flow in the opposite direction.

One good thing about these valves is that they can isolate a hydraulic system without any leakages.

These are examples of check valves. Image source: Aeronautics Guide

These hydraulics check valves come in a wide range of shapes and designs. Also, they are made from different materials such as stainless steel, zinc plated carbon, etc.

Depending on the type of application at hand, you may choose:

  • Hydraulic check valves with hardened seat
  • Line rapture valve
  • Shuttle valves that only allow for hydraulic fluid flow at high operating pressure

Apart from these three, there is another special type of check valve that is common in many applications. This is the pilot operated check valve.

5.3.4 Pilot-Operated Check Valves

A pilot operated check valve is a special type of valve that allows for fluid flow in two directions. Below is a standard symbol you can use to represent this valve in a hydraulic circuit.

This is a symbol of a pilot operated check valve. Image source: Hydraulic Valve

Normally, during the first phase, this valve allows fluid to flow in one direction like any other hydraulic check valve. However, in the reverse direction, a pilot pressure line will hold the valve open to allow for free fluid flow.

5.3.5 Pilot Logic Elements

Pilot logic elements are multi-purpose devices that perform a wide range of functions such as controlling pressure, direction and flow. Normally, these elements are used in cartridge valves to create a complex and functional hydraulic circuit.

Basically, these are cartridge valves you can conveniently install in hydraulic manifold blocks. With proper selection of pilot logic elements you can create a complex hydraulic circuit with optimal performance even at low pressure drop and high flow rates.

The pilot logic elements come in complex designs that may perform a range of functions such as:

  • Sensing presence of load
  • Bypass pressure in compensated pressure control
  • Optimizing flow in areas of low pressure drop
  • Designing energy efficient manifold blocks

This is a circuit diagram of a cartridge solenoid valve symbol.

There is a wide range of pilot logic elements you can incorporate in a hydraulic circuit to achieve unique performance requirements.

5.3.6 Lock Valves

Lock valves are available in a wide range of designs to lock hydraulic cylinders and sections of the circuit from possible damage and leakage. You can use lock valves whenever the directional control valve is in neutral position.

Some of the key functions of hydraulic lock valves include:

  • Prevent load drop and drift
  • Locks actuator and help relieve excess pressure
  • Act an emergency manual release
  • Prevent actuator cavitation and chatter

This is a complex circuit showing a hydraulic system with a manual lock system. Image source: Integrated Publishing

Again, hydraulic lock valves are available in a wide range of shapes and designs. You should choose one that fit your hydraulic system.

5.3.7 Hydraulic Servo Valve

A hydraulic servo valve is a device that monitors the flow of hydraulic oil in response to a specific command (electrical input signal) to control force, position, velocity or pressure in a system. You can classify these valves as closed-loop control devices and they can be single, two or three stages.

To achieve a precise control mechanism, the hydraulic servo valve uses a feedback control mechanism.

Above is an example of a two-stage servo valve. Image source: Hydraulic Valve

Normally, you can modify these systems to suit the desired application depending on the nature of the control system.

In summary, there are many types of hydraulic valves for a range of applications. Depending on the task at hand, you may choose either standard or custom hydraulic valves.

With all these in mind, now let’s discuss the various parts of hydraulic valve parts. This will give you an in-depth understanding of hydraulic valve design, hence, a high chance of choosing the right accessory.

Chapter 6

Hydraulic Valve Types

Hydraulic valves come in a wide range of designs to satisfy different functions such as:

  • Relieving hydraulic system from high pressure
  • Starting and stopping hydraulic fluid flow
  • Varying fluid flow
  • Regulating hydraulic system pressure/flow
  • Controlling direction of flow

Clearly, from this alone, you can notice that some valves can be complex in design with others having simple structure. Let’s have an overview of a hydraulic valve cross section:

This a diagram of a directional control valve fully disassembled.

The image above is of an actual directional hydraulic valve fully disassembled. As you can see, this valve alone has about 28 different parts.

For sure, this is quite overwhelming, especially for someone who is new to the hydraulic valve industry. The above diagram is quite different from the schematic representation of this accessory in the hydraulic circuits.

This image shows part of hydraulic valve. Image source: Hydraulics and Pneumatics

Remember, these are but a few samples of valves.

Furthermore, there are other hydraulic valve manufacturers who modify these accessories to suit unique requirements.

Why am I saying all these?

It will require a whole eBook to discuss all parts of hydraulic valves. Therefore, for the scope of this hydraulic valve eBook, I will focus on the basic parts. The basic hydraulic valve parts include:

  • Hydraulic valve body
  • Hydraulic valve bonnet
  • Hydraulic valve trim/internal elements
  • Hydraulic valve actuator
  • Hydraulic valve packing

In short, be it directional valve, check valve, needle, globe or pressure reducing valves; you’ll have at least these 5 parts that I am going to discuss in this section.

6.1 Hydraulic Valve Body

Also referred to as the shell, this section is the main boundary of the hydraulic valve. It holds all the components of the hydraulic valve together.

Normally, it is the main section that you’ll connect to the hydraulic valve system (hydraulic pipes). Depending on the type of material, you can join it to the pipe systems by:

  • Welding
  • Threads
  • Bolting

Here is an example of a hydraulic valve showing position of the body and other critical sections.

This is an image showing various parts of hydraulic valve.

Normally, a hydraulic valve body may be cast or forged into a wide range of shapes and designs. However, not every shape will be suitable for an efficient hydraulic valve.

You have to consider other aspects like:

  • What is the cost of fabricating a specific valve body shape or design?
  • Which is the most economical shape?
  • Does the material suit specific application of the hydraulic valve?

Choose a material that will resist fluid pressure, easy to fabricate and cost competitive.

For instance, hydraulic valves in the petroleum industry are different from those in the distilled water industry. This is basically due to the different types of fluids they control/regulate.

Let’s review a few materials so that you get exactly what I am talking about here:

Type of valve body materialMaximum pressure in the hydraulic system (MPa)Working temperature range in the hydraulic system (°C)
Gray cast iron0 to 1.50 to 250
Nodular graphite0 to 30 to 350
Brass0 to 3-200 to 200
Carbon steel0 to 13.50 to 450
Stainless steel casting0 to 13.5-150 to 750
Bronze0 to 3-200 to 200
Ductile iron casting0 to 30 – 350

From this table, it is quite clear that the type of hydraulic valve body will depend on the specific application. However, this is not all; other aspects such as characteristics of raw material or type of alloy will determine the exact type of material you should go for.

I found this resource quite useful: Type of Valve Material. Review it during your free time to get comprehensive details of material to consider for a hydraulic valve body.

6.2 Hydraulic Valve Bonnet

You can review the image above to know the exact location of the hydraulic valve bonnet. It acts as a cover to the valve opening.

Valve bonnets come in a wide range of shapes and designs. Depending on the design, they may function as a valve cover or support internal sections of the valve.

In most cases, they are made from the same material as the valve body.

The main challenges with this hydraulic valve part include:

  • Tend to complicate the manufacturing process of the valve
  • Can be a source of leakage is not properly fixed
  • Increase cost and size of hydraulic valve

In short, it is upon the manufacturer to evaluate and adopt a dependable system that can make hydraulic valve bonnet efficient.

6.3 Hydraulic Valve Trim

The internal parts of hydraulic valve are collectively referred to as the trim. In this section, you’ll learn about the various internal valve components.

As I had mentioned earlier, the number of internal parts of a valve may vary depending on the design and application.

These are the basic internal parts of a hydraulic valve. Image source: Wikipedia

You can learn about the part number and description in the table below:

Hydraulic valve part numberName of the hydraulic section
5Disc (on opening the valve)
6Hand wheel or handle (when the valve is open)
9Gland nut
10Fluid flowing on opening the valve
11Disc position (valve closed)
12Hand wheel or handle position (valve closed)

Now, let’s review some of these hydraulic valve components and parts:

6.3.1 Hydraulic Valve Spring

Spring helps to shift the position of the hydraulic valve disc. In the case of relief valves, they help to keep the valve shut until a required magnitude of pressure force is attained to open it.

This image shows the position of a hydraulic valve spring.

Image (A) shows a closed valve while (B) represents an open valve. By adjusting the screw at the top this valve will remain open; allowing hydraulic fluid to pass through.

Hydraulic valve springs are made from stainless steel, zinc plated steel and Inconel.

6.3.2 Hydraulic Valve Spool

A spool is an essential component of a hydraulic valve. At times, it is quite difficult to choose between spool and poppet types hydraulic valves.

I’ll focus on hydraulic poppet valve later in this section. For now, I’ll discuss hydraulic spool valve that is also referred to as a hydraulic directional valve.

For a fact, hydraulic spool valves are popular in most hydraulic applications. Below is a diagram showing the position of a spool in hydraulic valves.

This is an example of hydraulic valve spool.

These valves have seals that help control the hydraulic fluid flow. That is, whenever there is a shift in the hydraulic valve spool, seals travel along the bore of hydraulic valves, thereby opening its ports.

This allows for free flow. To understand where to use hydraulic spool valves, let me take you through the advantages and disadvantages of hydraulic spool valves.

Advantages of hydraulic spool valveDisadvantages of hydraulic spool valve
  • Works as sector valves. That is, choosing between vacuum and pressure section or high and low pressure.
  • Requires less force for actuation since pressure doesn’t affect its performance.
  • Works in vacuum
  • Can lock pressure downstream
  • Easy to balance since pressure entering the valve from any section does not affect its performance.
  • Seals on the spool are exposed to wear hence, they have short lifespan.
  • Low flow rate due to small internal surface
  • During actuation, all ports are momentarily opened, hence high chance of open crossover

Closely related to the spool is the poppet.

6.3.3 Hydraulic Poppet Valve

Ideally, the overall function of spool and poppet valves are virtually the same. However, unlike the spool, poppet covers the internal passage of the valve.

The poppet is held in its position by a spring and air pressure. Flow only occurs when the stem pushes away valve poppet after actuation.

This is a valve structure showing the position of a poppet. Image source: Hydraulics and Pneumatics

Now, let’s review the advantages and disadvantages of hydraulic poppet valves.

Advantages of hydraulic spool valveDisadvantages of hydraulic spool valve
  • High flow rate due to large internal surface
  • Precise control between positions due to closed crossover. That is, the poppet seals exhaust before opening for new flow.
  • Long product life due to less wear and tear.
  • Faster response time
  • They are normally unbalanced
  • Not suitable for vacuum applications
  • Requires high actuation force to overcome the pressure due to both air and pressure
  • Not suitable for holding pressure downstream since back pressure can open the valve.

6.3.4 Hydraulic Valve Disc and Seat

This is yet another essential component of hydraulic valve. The main functions of these parts include:

  • Disc is a third pressure boundary for hydraulic valve types with a bonnet
  • Hydraulic valve disc permits and prevents flow
  • By closing the disc, it may work as a pressure retaining component

Like other hydraulic valve and components, discs are made from a wide range of materials and designs. As a rule of thumb, the disc should have a fine finish to guarantee good sealing.

Hydraulic valve seats are in contact with the disc to form a leak-tight seal. You can choose from hard or soft seats depending on the type of application.

The position of a hydraulic valve seat is shown in the image above.

6.3.5 Hydraulic Valve Gaskets

Hydraulic valve gaskets prevent any leakages in the valve system. You can choose the type of gasket material depending on the type of application.

It is advisable that you adhere to the Current Good Manufacturing Practice (cGMP) when choosing the gasket material.

An example of hydraulic valve gasket

The hydraulic valve gaskets are available in a wide range of shapes and designs. Choose one that fits the shape and design of hydraulic valve component.

6.3.6 Hydraulic Valve Stem

It connects the actuator and disk. In most cases, they are connected to the hydraulic valve disc by welding or threading.

Unlike the hydraulic valve body, this is not a pressure boundary part. The images below show the position of two types of hydraulic valve stems:

A hydraulic valve stem

In any hydraulic system, you have to choose between a non-rising and rising stem.

6.3.7 Hydraulic Valve Balls

They are suitable for high-pressure, severe duty and high-tolerance applications.

An example of hydraulic valve ball

This is a versatile accessory made from either plastic (ABS, PVC, PP, etc.) or metal (stainless steel, titanium, brass, etc.), depending on the type of hydraulic valve.

6.4 Hydraulic Valve Actuator

A hydraulic valve actuator is the component that operates disc and stem assembly. There are many options of valve actuators such as:

  • Manual lever
  • Solenoid such as hydraulic valve coil
  • Pneumatic and hydraulic rams

Hydraulic valve coil or solenoid coil come in a range of designs and shapes depending on the unique specifications of the valve. Like other valve actuation mechanisms, solenoid coil help to open and close valves depending on the situation at hand.

In most cases, hydraulic valve manufacturers tend to have both standard and custom design hydraulic valve coils.

A symbol of hydraulic cartridge solenoid valve

6.5 Hydraulic Valve Packing

Packing materials such as flax or Teflon prevent leakage in the hydraulic valves. They are packed to form a seal between various components of the hydraulic valve systems.

With all these, I now believe that you can analyze hydraulic valve components besides choosing one that is suitable for your unique requirements. However, this alone is not enough.

You need to know how to repair or troubleshoot hydraulic valves. This is what you’re going to learn in chapter 7 of this hydraulic valve eBook.

Chapter 7

Hydraulic Valve Troubleshooting

Always remember safety first

It doesn’t matter whether you’re planning to troubleshoot a pressure or directional control valve. You need to take all the necessary precautions to go about this process successfully.

Before I start on the actual process of troubleshooting hydraulic valves, let’s discuss the key safety measures you MUST consider.

7.1 Safety in Hydraulic Valves

As a general rule, you must read the manufacturers’ technical manual. Here, you will find all the necessary precautions to consider when handling any hydraulic valve.

Below are the key pillars of safety in hydraulic valve troubleshooting process:

Wear full face protection: You need a full face protection when working in any hydraulic system. Therefore, you should choose high quality and reliable safety goggles.

You must wear safety gear when handling any hydraulic system.

High quality goggles should have the right surface treatment such as a permanent anti-fog solution and anti-scratch coating among other reliable surface treatments.

Release all hydraulic pressure within the circuit: This will reduce the possibility of the fluid spilling on your face or any possible wastage. For instance, ensure the hydraulic pump or actuator is off before you start troubleshooting the hydraulic valve.

Identify every part of the valve and the function of each component: With this information, it will be easy to know why a specific fault occurs. I had discussed various types of hydraulic valve in chapter 5 and hydraulic valve components in chapter 6.

This information will enable you to safely troubleshoot hydraulic valves without causing damage to other parts.

Furthermore, you should know the exact specification of each valve. This should include the working temperature, flow rate and operating pressure.

Remember, a hydraulic fluid with a high operating temperature, pressure and flow rate can cause devastating accidents. In many oil and gas industries, systems at a high pressure do cause serious injuries and at times death.

Wear an overall, gloves and industrial boots: They will protect your body from possible injury or being in contact with hydraulic fluid that could be harmful.

These are examples of industrial gloves. Image source: America West Drill Supply

Apart from these, you should note the following:

  • Only trained personnel should inspect and troubleshoot hydraulic valve
  • Use only the recommended tools and equipment to tighten, loosen or adjust sections of the hydraulic valve system
  • Follow all instructions as stipulated in the manufacturer’s manual

Don’t ignore or take these safety measures for granted. Always remember this at all times:

“Machines have no brain, use yours”

With all these in mind, let’s review possible faults in hydraulic valves and how to fix them.

7.2 Step-by-step Process on Troubleshooting Hydraulic Valves

In this section, you’re going to learn about the most common problems you can encounter when operating hydraulic valves and how to correct them. For the scope of this section, I will focus on the following valves:

  • Volume control valves
  • Pressure control valves
  • Directional control valves

Generally, these are the most common types of valves you’ll encounter hydraulic circuits. Again, knowing how to troubleshoot them will help to fix problems or errors in other special valves.

NOTE: Always remember to refer to the manufacturer’s manual and instructions when troubleshooting and repairing hydraulic valves. At times, hydraulic system manufacturers modify these valves to meet specific applications of their machines.

7.2.1 How to Troubleshoot Volume Control Valves

Broadly, we classify all the available volume control valves as:

  • Flow-divider valves
  • Flow control valves

In hydraulic circuits, you can represent these valves as:

A circuit diagram of cartridge flow valve

On the other hand, the actual valve looks like this:

This is the actual flow control valve.

In most cases, when you’re using the flow control valves, you may experience the following problems in the hydraulic circuit.

1. Valve has varying flow rate

Variation in the flow rate can be devastating and the hydraulic system is likely to malfunction. Normally, this variation could be due to a range of factors such as leaking motor, oil with high viscosity, leaking cylinder, valve spool binding in the body, dirty oil and insufficient pressure drop across the valve.

In short, by inspecting and fixing these factors, you will eliminate any possible variations in flow.

2. Erratic pressure in the hydraulic system

At times, you may experience erratic pressure in the hydraulic circuits. In case you suspect that this could be due to the flow control valve or flow divider valve, then it could be due to dirty oil, worn out seat or poppet.

3. Existence of improper flow

Improper hydraulic fluid flow can be costly to the system. Normally, there are six main causes of improper flow as far as the volume control valves are concerned.

These include:

  • Hydraulic oil may be too hot, consider regulating the temperature.
  • Valve not adjusted properly so review the operating parameters
  • Relief valve could be leaking
  • Movement of the valve piston could be restricted
  • Check all passages and orifices if there is any restriction
  • Valve piston could be cocked

By considering all these, I am sure you will eliminate this problem.

4. High oil temperature in volume control valve/hydraulic system

High temperature will undermine the performance of various parts of a hydraulic circuit. At times, the entire system may breakdown.

In case of this situation, you should check the following:

  • Adjust the pump speed; you could be using improper settings.
  • Check all connections within the volume control valve
  • Malfunctioning relief system

In short, these are the common problems you’ll face when operating any type of volume control valve.

7.2.3 How to Troubleshoot Pressure Control Valves

Pressure control valves play an integral in hydraulic circuits. In this section, you will learn how to troubleshoot 4 types of pressure control valves namely:

  • Hydraulic relief valves
  • Pressure reducing valves
  • Pressure sequence valve
  • Unloading valves

Now, let’s have an overview of all possible problems that you will encounter in hydraulic systems with these types of valves. How to Troubleshoot Hydraulic Relief Valve

Below is an image of a circuit representation of a hydraulic relief valve.

This is a hydraulic cartridge relief valve.

Whenever you’re using a hydraulic relief valve, there is a possibility of facing the following problems:

1. Erratic or low pressure in relief valves

There are many factors that may lead to this problem and they include:

  • Valve could be partially open due to dirt, burrs or chips
  • Sticking valve piston
  • Sprig ends could be damaged or weak
  • Cocking seat
  • Blocked orifice of balance hold
  • Damaged seats or poppets

Apart from these, another common aspect is the improper adjustment of the relief valve settings. By assessing hydraulic valves based on these aspects, the systems will operate optimally.

2. Low or inadequate system pressure

At times, pressure in the hydraulic system maybe inadequate or drop to zero. In such situations, you should inspect the hydraulic relief valve for:

  • Partially open valve due to dirt, burrs or chip
  • Damaged poppet or seat
  • Cocking, loose or binding valve components
  • Either the balance or orifice hole could be plugged
  • Valve poppet does not seat
  • Loose fitting in the valve

By adjusting any of these parameters, your relief valve will operate optimally at all times.

3. Existence of noise or chatter

Noise is an annoying phenomenon. You should eliminate or reduce it at all cost.

In fact, the presence of “abnormal” noise is a clear indication of a malfunctioned relief valve. Here are the critical aspects to consider whenever there is noise or chatter:

  • Faulty poppet, spring or seat
  • Highly viscous oil
  • Line pressure could be having excessive return
  • Relief valve pressure setting could too close to some valves in the hydraulic system

You should try to adjust these settings.

4. Adjusting relief valve results in excessive system pressure

Normally, this could be due to the restricted drain line and faulty hydraulic valve spring.

5. Overheating hydraulic relief valve

Whenever your hydraulic valves begin to overheat, know that it could be due to leaking valve seat or a highly viscous oil. Some valves may overheat due to continuous operation.

I hope by considering all these, your hydraulic relief valve will function without any problems. How to Troubleshoot Pressure Reducing Valves

Normally, a faulty hydraulic pressure reducing valve may cause erratic pressure within the system. Such hydraulic systems are considered unreliable.

To restore it, you need to inspect the pressure reducing valve for:

  • Dirty oil
  • Check valve settings and adjust it accordingly
  • Worn out valve component such as poppet, spring, seat and spool bore.
  • Restricted balance hole or orifice
  • Valve spool could be binding in the body
  • Blocked drain line
  • Spring ends may be square

Again, even as you replace the various components of a hydraulic pressure reducing valves, ensure they are compatible. If possible buy these components and accessories from a recognized dealer or original manufacturer. How to Troubleshoot Pressure Sequence Valves

Pressure sequence valves play an integral role in hydraulic systems. Below are some common problems and how to solve them:

1. When the secondary operation is too slow or in the absence of movement

Normally, there are three possible causes and they include:

  • Whenever the spool binds with the sequence valve body
  • When the setting of a relief valve and sequence valves are too close.
  • Sequence valve setting is too high

By adjusting your hydraulic sequence valves based on these, you’ll definitely improve their performance.

2. Secondary operation takes place prematurely

Again here, you need to consider two main aspects:

  • Check if the setting of the valve is too low and adjust it accordingly
  • Magnitude of load on the primary cylinder could be high

These are simple operations you can adjust to ensure optimal operation of the valve.

Apart from these two, there are other problems that can affect the efficiency of the hydraulic sequence valves. Whenever you notice any problem with these valves, you need to:

  • Check the valve installation settings and tighten loose parts such as valve covers
  • Confirm whether there are worn springs, valve-stem seat or valve plunger.
  • Clean the orifices, drain, plunger seat and moving parts; there could be oil impurities or foreign matter
  • Adjust the gasket, it could be leaking
  • Orifice may be too large, hence causing jerky operation

I am sure these hydraulic valve troubleshooting tips are resourceful. How to Troubleshoot Unloading Valves

You need to pay attention to the unloading valves in situations where they fail to unload a hydraulic pump. In such situations, you should try the following:

  • Check the valve setting, it could be too high
  • The spool could be binding with the pipe’s body
  • Pump may not build up the required unloading valve pressure

With this information, I am sure troubleshooting pressure control valves will be a simple process.

7.2.4 How to Troubleshoot Directional Control Valves

As you’ve seen in the previous chapters, directional control valves play an integral role in the hydraulic circuits. Like other hydraulic valves, these valves can be classified based on the number of ways and positions.

They include rotary spool and check valves.

In this section, I am going to discuss 5 possible problems you’ll encounter in hydraulic circuits with directional control valves.

This is a directional control valve symbol.

This is how to troubleshoot directional control valves:

1. An incomplete shifting in directional control valves

There are a number of factors you can correct whenever you experience incomplete shifting in these valves. These include:

  • Replace worn out components such as solenoid, center spring and control linkage.
  • Pilot pressure could be insufficient
  • Adjust hydraulic valve spool accordingly

Apart from this, another common problem is the creeping or drifting of the actuating cylinder.

2. Actuating cylinder of the directional control valve creeps or drifts

To correct this problem, you need to ensure the valve spool shifts completely and it is centered properly. Also, you should check for any leakages around the valve seats and past the cylinder piston.

Always form the habit of replacing worn out components of the valve, especially the spool.

3. With the hydraulic directional valve at a central position, what causes the cylinder load to drop?

Well, this could be due to loose lines of the valve housing, leaking relief valve, O-rings and plugs. Again, the springs could be worn out or broken.

You should consider making all the necessary adjustments on the above components.

4. Oil heats up

There are two reasons here, either the valve components are not in the right position hence, you must make some adjustments or the valve seat is leaking.

5. The Cylinder load keeps dropping slightly when raised

Here, you have to check whether the seat and spring are defective or faulty. Furthermore, you should adjust the position of hydraulic valve spool.

As you can see, troubleshooting hydraulic valve is not a simple and easy process. You need a lot of experience in the hydraulic valve industry.

It is for this reason that I recommend you contact the original hydraulic valve manufacturer. This is because you may not have the tools and equipment to conduct some of these tests.

Remember, a hydraulic circuit may have a series of valves. You’ll hardly find complex machines such as hydraulic power packs in tractors with one or two valves.

With all these in mind, let’s review the critical applications of hydraulic valves in the next chapter before considering top hydraulic valve manufacturers in the word.

Chapter 8

5 Most Important Applications of Hydraulic Valves

Hydraulic valves play an integral in many hydraulic systems. For instance, you can use them to regulate or redirect the hydraulic fluid flow.

By doing this, your intention will be to achieve a certain threshold of hydraulic energy.

I know there are thousands of ways you can use a hydraulic valve. However, in this chapter I will focus on only 5 most important applications of hydraulic valves.

Let’s review these applications one at a time:

8.1 Lift

This is a machine that uses hydraulic systems to move or lift objects. That is, a predetermined amount of pressure is exerted on the fluid that in turn develops a force that does the intended work.

This is an example of hydraulic elevator. Image source: Electrical Know How

There are many types of hydraulic lifts and you may classify them depending on a wide range of aspects. These may include design, application, etc.

For instance, you may have a direct acting hydraulic lift, suspended hydraulic lift, scissor lifts, carouse lifts, two-post lifts, etc.

The bottom line is, to achieve the desired magnitude of force you need to regulate the hydraulic fluid flow. This is possible when you choose the right valves.

8.2 Hydraulic Power Pack

This is a stand-alone device that helps users to control hydraulic systems by choosing valve to open and close. That is, they can power or control hydraulic systems to operate other machines.

Hydraulic power packs come in a wide range of shapes and designs such as large designs, stationary and portable units.

This is a technical drawing of hydraulic power pack. Image source: Target Hydraulics

Hydraulic power packs use hydraulic valves to control both flow and pressure limits. These may include pressure control valves and directional control valves.

Whether you opt for an AC or DC hydraulic power packs, you may use it in dump trailers, telescopic logistic equipment, car tailgates, electric push carts, electric pallet lifts, etc.

In short, hydraulic power packs depend on valves to coordinate all its operations.

8.3 Mobile Hydraulic

I know you must be wondering why mobile hydraulic forms an integral part of this section.

The truth is, unlike other hydraulic applications, in mobile hydraulic systems, demand for fluid flow and pressure varies greatly between different functions over time. This is not always the case in industrial hydraulic systems.

Therefore, to have a cost effective, compact and reliable mobile hydraulic system, there is need to select appropriate open-center valves.

This is a mobile hydraulic system with an open-center valves and a fixed displacement pump.

You need versatile valves that can provide appropriate damping when handling large inertia loads. Examples of mobile hydraulic systems include hydrostatic fan drive and tractor systems.

In short, without valves, there will be no mobile hydraulic systems.

8.4 Hydraulic Press Machine

Hydraulic press is a device that uses hydraulic systems to generate enormous compressive force. Since these machines were invented in 1795 by Joseph Bramah, they play an integral role in clinching, blanking, punching, forging, metal forming, deep drawing, etc.

This is a hydraulic press machine.

Some of these applications require precise control of hydraulic fluid flow. To achieve this, the machine must have highly effective and reliable hydraulic valves.

8.5 Material Handling

Hydraulic handling machines help to move, control, protect and store material or goods. This involves precise coordination of parts directly or indirectly involved in handling the equipment.

This is an example of material handling equipment.

Examples of material handling equipment include industrial trucks, conveyor systems, racking systems, hoppers, etc. The type of valve in a system will depend on the specific motion you intend to achieve during the process.

As you can see, hydraulic valves play an integral role in all machines that depend on hydraulic fluid to do the work. Normally, it is upon the manufacturer of the hydraulic machine to choose appropriate valves.

The hydraulic valve should guarantee efficient fluid transmission while minimizing unnecessary wastages.

Having mentioned all these, let’s go to the last chapter of this eBook where you will learn about the top 10 hydraulic valve companies in this world. That is, companies that design, manufacture or have invested in hydraulic valve research.

Chapter 9

Top 10 Hydraulic Valve Manufacturers in Global Market

Today, there are many hydraulic valve manufacturers with every company claiming to have the know-how in the industry. However, this may not be true for all companies.

For instance, there are those companies that do not adhere to the international standards such as using the right hydraulic valve ISO symbols. This is a high level of unprofessionalism.

In this section of our hydraulic valve eBook, you’ll learn about top 10 hydraulic valve manufacturers in the global market. Therefore, whenever you need a hydraulic valve, it is important that you compare what each company has to offer.

These hydraulic valve manufacturers include:

9.1 HydraForce

HydraForce was founded in 1985 in Chicago. Currently, the company has opened either manufacturing or distribution outlets in many parts of North America, Europe and Asia.

As one of the leading hydraulic valve manufacturers, HydraForce has over 120 stocking distributors. Some of its products include solenoid on/off, multi-functional, pressure control and flow control valves, just to mention a few.

HydraForce homepage

Click this link to learn more about HydraForce.

9.2 Sun Hydraulics

Since 1970, Sun Hydraulics has grown to be a household name in the hydraulic valve industry. In 1997, Sun Hydraulics became a public company with the stock symbol SNHY listed on NASDAQ.

It is one of the leading designer and manufacturer of hydraulic valves and manifold blocks. Some of its main products in this category include pressure control, flow control, load holding, solenoid operated, logic elements, etc.

Sun Hydraulics

Follow this link to learn more about Sun Hydraulics.

9.3 Bosch Rexroth

Bosch Rexroth designs and manufactures a range of hydraulic valves for many applications in mechanical plant engineering. Since its inception nearly 200 years ago, the company has partnered with over 29,500 companies and businesses globally.

Bosch Rexroth is known for its energy efficient valves and custom solutions. It has production sites in 20 countries with associate partners in 80 countries.

Bosch Rexroth

Bosch Rexroth hydraulic valves include on/off valves, manifold blocks, proportional and servo valves, just to mention a few. Click this link to access more information about Bosch Rexroth.

9.4 Bucher Hydraulics

Bucher Hydraulics was founded in 1923 and it has evolved to be a global leader in the hydraulic valves industry. Being an innovation driven company, Bucher Hydraulics has the know-how in designing hydraulic valves to unique customer specifications.

Bucher Hydraulics designs and manufactures many valves such as flow preventing, directional spool, directional seat and safety relief, among other complex hydraulic systems.

Bucher Hydraulics

Click this link to learn more about Bucher Hydraulics products.

9.5 Delta Power Company

Delta Power Company is based in America and it designs and manufactures a range of hydraulic manifold blocks and cartridge valves. Its main products include solenoid directional controls, proportional controls, mechanical directional controls and motorized valves.

Other hydraulic valve accessories are also available.

Delta Power Company

Click this link to learn more about the Delta Power Company hydraulic valve products.

9.6 Deltrol Fluid Products

Deltrol Fluid Products is a Chicago based hydraulic valve manufacturer. Since 1963, Deltrol Fluid Products has devoted its resources to designing high quality and cost competitive hydraulic valves.

It manufactures in-line accessories for both pneumatic and hydraulic systems. Deltrol Fluid Products hydraulic valves include cartridge valves (solenoid, check, motion control, flow control, relief, etc.), zero profile valves (check, relief, shuttle, flow control, motion control, etc.), inline valves and custom manifold blocks, among other accessories.

Deltrol Fluid Products

Follow this link for an in-depth overview of the Deltrol Fluid Products hydraulics products.

9.7 Saroit Hydraulics

Saroit Hydraulics is one of the leading hydraulic valve manufacturers in China. This company has specialized in hydraulic manifold blocks such as cartridge valve manifold, standard manifold valve housing, custom hydraulic manifolds and standard manifold blocks.

Also, available are the hydraulic cartridge valve such as cartridge check valve, cartridge flow valve, cartridge hand pump, cartridge needle valve, cartridge relief valve, cartridge solenoid valve, hydraulic directional valve and hydraulic shuttle valve.

Saroit Hydraulics offers one of the best OEM partnerships. The company has high-tech manufacturing equipment alongside the know-how in hydraulic valve designs.

Saroit Hydraulics

You can click this link to learn more about Saroit Hydraulics products.


Since HYDAC was founded in 1963 it has grown to be a household name in the hydraulic valve industry. Currently, the company has over 50 offices and 500 trade partners globally.

HYDAC collaborates with leaning and research institutions in its efforts to encourage innovation in hydraulics valve industry. At the moment, HYDAC has many products that include cartridge, inline connection, sub plates and slip-in valves.

They come in both standard and custom designs.


You can follow this link to learn more about HYDAC hydraulic valve products.

9.9 Parker Hannifin

Parker Hannifin has been in the hydraulic valve industry for more than100 years. The company has diversified its operations to meet the dynamic needs in hydraulic systems control.

Among the key hydraulic valve products that Parker Hannifin designs and manufactures include manual, motor electrically or solenoid air actuated. These include a range of valves such as angle body, ball, butterfly, check, cartridge, pilot, flow control cartridge, manifold, diaphragm and bellow valves, just to mention a few.

Parker Hannifin

Follow this link to learn more about Parker Hannifin hydraulic valves.

9.10 Eaton

Eaton designs and manufactures a range of hydraulic systems. Its products deliver unmatched performance in diverse applications.

Eaton is known for its industrial valves (check, pressure control, servo valves, etc.); mobile valves (CMA advanced mobile valve) and screw-in cartridge valves (check valves, directional controls, pressure control, solenoid valves, etc.).


Click this link to learn more about Eaton hydraulic valves.

With these companies, I am sure you’ll get appropriate valves that meet unique requirements of any application. Remember, each company has unique manufacturing capability.

Take for instance, Saroit Hydraulics is known as an OEM hydraulic valve manufacturer while Eaton is popular for its mobile hydraulic systems.

Now that we have come to the end of this hydraulic valve eBook, I believe you can choose an appropriate accessory for a suitable application. As you can see, there are many hydraulic valves for different applications.

You need to take time to review all critical aspects that may affect the valve performance. These may include design, applications, type of material etc.


From this hydraulic valve eBook, I am sure you’ve learnt the following critical aspects: definition, working principle, symbols, functions, types, parts, troubleshooting, applications and manufacturers of hydraulic valves.

This is basically the first stepping stone to becoming hydraulic valve expert. As you read this eBook, it is important that you see these valves physically to have an in-depth understanding of every aspect of these products.