Hydraulic Solenoid Valve - How They Work

A hydraulic solenoid valve is a solenoid controlled directional valve used in a hydraulic system for opening, closing or changing the direction of flow of the liquid. The valve operates with a solenoid, which is an electric coil wound around a ferromagnetic core at its center. The valve consists of various chambers also called ports. The solenoid is used for sliding the spool within the valve, opening or closing the ports. The spool is the cylindrical component which serves the function of the valve by either blocking or allowing the flow of liquid through these ports, depending upon its position.

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Hydraulic solenoid valves are widely used in industries like manufacturing, aerospace, construction and many others that require hydraulic systems. Figure 1 is an example of a hydraulic solenoid valve.

Table of contents

• Directional control valves
• Valve design
• Design options
• Industry examples
• Points of attention and selection criteria
• FAQ

Directional control valves

The directional control valves are designed to start, stop or change the direction of the fluid flow. These valves are most commonly used in hydraulic and pneumatic systems. We discuss only the hydraulic applications for the purpose of this article.

Hydraulic solenoid valves

The hydraulic solenoid valve is a directional control valve widely used in hydraulic systems to change, allow or restrict the flow of liquid. The valve uses solenoids (X and Y) on either side of the valve for actuation as seen in the figure below. The valve consists of a cylindrical spool (Z) with land (larger diameter) and grooves (smaller diameter). The land blocks the flow while the groove allows the flow through the valve.

The directional valves are generally represented by the number of ports and number of switching positions. In the 4/3-way valve hydraulic valve in above, 4 represents the number of ports and 3 represents the number of positions. P is the pressure port, A and B are working ports and T is the return port.

When the solenoid X is actuated, the spool is pulled towards the left by the electromagnetic force. When solenoid Y is actuated, the spool slides towards the right. This sliding of the spool opens, closes or changes port connections, which alters the direction of the flow.

Valve design

4/3-way valve

A 4/3-way valve has 4 ports and 3 positions. It is the most common type of valve used in hydraulic circuits. Depending on the spool design, ports can be open, closed, or connected to certain inputs/outputs. Figure 3 below is a common example, but there are additional spool designs. The spool below can be in 3 different positions: P-A and B-T (Figure 3 left), closed (Figure 3 middle), or A-T and P-B (Figure 3 right).

As seen in circuit function 1 (Figure 3 left), when the spool is moved to the right, port A is connected to port P and port B is connected to port T.  Circuit function 2 (Figure 3 middle) represents a closed center valve with all the ports blocked. When the spool is moved to the left, port P is connected to port B and port T is connected to port A.

4/2-way valve

A 4/2-way valve has 4 ports and 2 positions. A and B are two working ports, P is the pressure port and T is the return port.

These valves can have a single or double solenoid design. They can be connected in a normally open or closed position, therefore, there is a spring to return it to its normal position. A single solenoid valve shifts the spool when the solenoid is actuated and returns to the original position once de-energized. In a double solenoid valve, the spool shifts when one solenoid is energized and returns when the other is energized. It is important to note that only one solenoid should be energized at any given time.

Design options

These hydraulic solenoid valves are available with features like socket head cap screws with hexagon socket, magnetic coil, sealing set for Pohl tube, O-ring set for connection plates or, blind plate including 4 O-ring. These features support reliable fastening and tight sealing to prevent leakage during the process.

Detent mechanism

A detent mechanism can be a magnetic or mechanical catch to prevent the motion of the spool. Some hydraulic solenoid valves use this detent mechanism to hold the spool in an open or closed position when de-energized. When energized, the spool is released, and it returns to its original neutral position. In a 2-position valve, the valve can be detented for spool to remain in either position. For a 3-position valve, the valve can be detented to remain in any of its three positions.

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Industry examples

Hydraulic solenoid valves are used in a wide range of applications that use a hydraulic system. Common hydraulic solenoid valve applications are:

• Water supply system
• Turbine system
• Fuel/gasoline supply system
• Wastewater treatment plants
• Process control in manufacturing plants
• Hydraulic motors, breaks, pumps in automotive industry
• Hydraulic machinery in aerospace and marine industries
• Heavy machinery in construction and landscaping
• Machinery in agricultural sectors

Points of attention and selection criteria

1. Number of ports and positions: This should be selected based on the requirement of your application.
2. Spool action: This should be based on whether your application requires the spool to return back to the center or stay in place when deenergized.
3. Flow: The flow requirement for the application will help in determining the size of the valve.
4. Material: The material of the valve should be compatible with the properties of flowing media.
5. Temperature: The valve materials can withstand the minimum and maximum temperature requirement of your application. Temperature is also essential in determining valve capacity as it affects the viscosity and flow of the fluid.
6. Pressure: The valve must be able to withstand the maximum pressure required for your application.

FAQ

What is a hydraulic solenoid valve?

A hydraulic solenoid valve is a solenoid controlled directional valve used in hydraulic system for opening, closing or changing the direction of flow of the liquid.

What is a spool?

Spool is a cylindrical component within the valve that helps with opening, closing or changing the direction the flow in a hydraulic or pneumatic system.

What are the functions of the hydraulic control valves?

Hydraulic control valves are used to adjust the flow rate of hydraulic fluid in a hydraulic system. These valves have a port that is able to be adjusted so that the flow area may be changed to provide an alteration in the flow rate through the valve.

How Does a Hydraulic Control Valve Work?

Within a hydraulic system, a flow-control valve will be used to control the rate of flow to hydraulic cylinders and motors, which in turn will impact the speed of both of those devices. Hydraulic flow-control valves also have a secondary function of managing the energy transfer rate at a specified pressure.

1. What is the hydraulic control valve?

The hydraulic control valve is a kind of valve that is controlled by water pressure. It consists of the main valve and other accessories such as conduit, pilot valve, needle valve, sanitary ball valve, and pressure gauge.

2. What are the types of hydraulic control valves?

According to different purposes of use, functions, and occasions of use, there are remote control float valves, pressure relief valves, slow-closing check valves, flow control valves, hydraulic electric control valves, and water pump control valves. According to the structure, it can be divided into diaphragm type and piston type.

3. The diaphragm type hydraulic control valve mechanism VS piston type hydraulic control valve

The diaphragm type and piston type hydraulic control valve share the same mechanism.

They both use the pressure difference between upstream and downstream as power. They are controlled by a pilot valve to make the diaphragm (piston) perform the hydraulically differential operation, which is completely automatically adjusted by hydraulic power so that the main valve disc is fully open or fully closed or in the regulatory state. When the pressure water entering the upper control chamber of the diaphragm (piston) is discharged to the atmosphere or downstream low-pressure zone, the pressure on the bottom of the valve disc and diaphragm is larger than the pressure on the top, pushing the main valve disc to fully open position.

When the pressure water entering the upper control chamber of the diaphragm (piston) can&#;t be discharged to the atmosphere or downstream low-pressure zone, the pressure on the top of the valve disc and diaphragm is larger than the pressure on the bottom, pushing the main valve disc to the fully closed position.

When the pressure in the upper control chamber of the diaphragm (piston) is between the inlet pressure and outlet pressure, the main valve disc is in a regulated state and its position of adjustment depends on the joint control effect of the needle valve and adjustable pilot valve of the conduit system. The adjustable pilot valve can use the downstream outlet pressure to enlarge or tighten the valve opening, thereby changing the pressure value in the upper control chamber of the diaphragm (piston) and controlling the adjustment position of the main valve disc.

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