Hydraulic Spool Valve – The Ultimate Guide

Spool valves play an integral role in hydraulic systems. Actually, it forms an important component of hydraulic power systems.

If you are wondering why you need hydraulic spool valves or where to install these valve systems – well, this guide has all the information you are looking for.

What is a Hydraulic Spool Valve?

A hydraulic spool valve is a flow regulatory device that has seals along the surface. The seals are built with spools that are moved by an actuator to block and release fluid.

Hydraulic Spool Valve
Hydraulic Spool Valve

Hydraulic Spool Valve Symbol

Multiple symbols are used to represent hydraulic spool valves. The different symbols are used for different types of hydraulic spool valves.

This symbol represents a two-way spool valve. It allows for the flow of fluid in two different directions.

The symbol above represents a four-way spool valve. This spool valve has four connection ports that can allow flow in four different directions.

This symbol stands for a four-way three-position spool valve. It has four connection ports and it can be placed in three different positions.

Advantages of Spool Valve in Hydraulic System

The benefits of using a hydraulic spool valve in your system are;

  • You can opt to use a spool valve in place of a selector valve as it can control flow in both directions depending on the pressure.
  • Hydraulic spool valves can be coupled with a vacuum making it multifunctional
  • They do not require a lot of effort on the actuator since pressure does not affect the valve
  • The spool’s positioning is not affected by the movement of fluid in the system since the valve is stable.
  • Hydraulic spool valves help prevent backward flow that is caused by reduced pressure.

Limitations of Hydraulic Spool Valves

The limitations of using hydraulic spool valves are;

  • The spool reduces the internal area of the valve slowing down the rate of the flow of fluid
  • When turning the spool as you actuate all connection ports are exposed for a short time
  • The metal used in designing the sliding fits may allow for leakage as they are fitted against a metallic body.
  • Hydraulic spool valves are more prone to wear and tear on the mounted seals shortening the valve’s lifespan.

Types of Spool Valves in Hydraulic Systems

There are different types of spool valves used in hydraulic systems. They include;

Sliding spool valve

This type of spool valve is designed with cylindrical lands, grooves, and cross-sections. It has a spool with grooves that is moved by sliding inside a sleeve. The valve moves in and out allowing fluid to be transported through the intake and outtake connection. It can control both the flow and direction of fluid in hydraulic systems.

Sliding Spool Valve
Sliding Spool Valve

Rotary spool valves

This type of spool valve is manufactured with circular lands and grooves. It has an x-shaped core that rotates inside of a fixed tube-like sleeve. It has four ports located at the center that are used to transport fluid in and out of the system.

Rotary Spool Valve
Rotary Spool Valve

Hydraulic Solenoid Valves vs Hydraulic Spool Valve

Hydraulic solenoid valves are designed with a magnetic core that is wrapped with an electric coil. The valve uses electrical impulses to control the opening and closing of the ports. You can also use it to control the direction of flow.

Hydraulic spool valves on the other hand are fitted with manual actuators. These levers are used to control the spool allowing it to move it to open or close the ports. Just like solenoid valves, you can also use them to change the direction of the flow.

Solenoid Valve
Solenoid Valve

Parts of Hydraulic Spool Valves

Hydraulic spool valves are comprised of the following parts;

  • Valve body; this is the external part of the valve that encases the inner components of the valve
  • Seal; It is a barricade located at the opening of the valve that is used to prevent fluid from flowing through. When you remove the seal fluid flows through.
  • Spool; The spool is a cylindrical metal that crosses through the internal opening in the valve. It carries the seals that are used to regulate flow.
  • Spool land; This is the part of the spool that combines with the seal to prevent fluid from leaking from the valve.

How Spool Valves in Hydraulic Systems Work

Spool valves act as regulatory devices inside hydraulic systems. The valve comprises a spool that has seals. Its spool is turned using an actuator that can either be manually or using buttons or levers.

You can rotate or slide the spool to remove the seal and allow the fluid to pass through. It can also be used to change the direction of the flow by opening up different portals and preventing backflow.

Hydraulic Spool Valve Working Principle
Hydraulic Spool Valve Working Principle

Troubleshooting Hydraulic Spool Valves

It is important that you properly maintain your hydraulic spool valves to ensure that you can use them for a long time.

Regular maintenance also allows you to spot potential problems and fix them before there is irreparable damage to the systems. Common problems experienced by hydraulic spools include;

Internal Leakage

Hydraulic spool valves are prone to getting internal spills. An increase in the leakage leads to a loss of pressure in the system which is the cause of worry. This problem is often a result of contamination in the oil that causes wear in the spools resulting in gaps.

Internal leakage can be rectified by emptying the oil in the system and taking apart the valve. You are required to properly clean it before reassembling it and filling the system with clean oil. Consulting an expert if you are unable to properly carry out the disassembling is recommended.

External Leakage

Faulty valves or an ill-fitted seal can result in external leakage. External leaks may require you to purchase a new valve especially if the leakage is originating from the body of the valve.

Regulating the pressure within your system after installing the new valve will prevent the problem from reoccurring

Leakages resulting from seals not properly functioning can be mended by replacing the spools and the seals.

Spool Binding

Spool binding is another problem that can be caused by several things. It may be a result of contamination, too much heat, poor mounting, and valve links getting misaligned.

It is therefore important for you to identify the cause of spool binding.

Regulating temperatures, properly aligning the valve links, draining contaminated fluid, and properly mounting the spool can be done to rectify the problem.

If you are unable to carry out any of these procedures it is best to consult an expert to prevent causing further damage to the valve.

Applications of Spool Valves in Hydraulic Systems

There are several applications in which you can use spool valve hydraulic systems. These applications include hydraulic systems in which oil provides energy for carrying out tasks such as

  • Automotive and aerospace hydraulic systems
  • Construction equipment including; jacks, cranes, forklifts,
  • Agricultural equipment such as pumps etc.

At Target Hydraulics, we will help get high-quality and precise hydraulic spool valves for your systems.

More Resources:

Hydraulic Proportional Valve – Source: TARGET HYDRAULICS

Types of Hydraulic Valves – Source: IQS DIRECTORY

Hydraulic Solenoid Valves – Source: TARGET HYDRAULICS

All About Hydraulic Valves – Source: THOMASNET

Hydraulic Check Valve – Source: TARGET HYDRAULICS

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