Hydraulic Solenoid Valve: Components, Working Principle, Functions, and Types

hydraulic directional control solenoid valve
Figure 1: Hydraulic solenoid valve.


In hydraulic systems, hydraulic solenoid valves play a vital role as control components. This article will introduce the components, functions, working principle and common types of hydraulic solenoid valves.

1. Main Components of Hydraulic Solenoid Valve

The hydraulic solenoid valve is an important component used to control the liquid flow in the hydraulic system. It usually contains the following main components:

Valve Body: It is the main component of the hydraulic solenoid valve. Usually made of metal materials, it has the function of carrying pressure and connecting pipelines.

Valve Spool (Valve Core): It is a moving part located in the valve body and is usually made of metal and has good sealing performance. Its position determines the opening and closing state of the valve.

Solenoid Coil: It is the power source of the hydraulic solenoid valve. It controls the working state of the solenoid coil through the input of current, and then controls the action of the valve core.

Spring: As a mechanical force component, spring is often used in hydraulic solenoid valves to restore the initial position of the valve core or provide the necessary closing force.

Seal: Often made of rubber, polyurethane and other materials, it is used to ensure that the internal fluid of the hydraulic solenoid valve does not leak.

Hand Lever: It is a manually operated component in a hydraulic solenoid valve. It is usually used to manually control the switching state of the valve when there is no power or power failure.



solenoid coils of different sizes
Figure 2: Solenoid coils.


Different types of hydraulic solenoid valves may differ in structure and components, so select or design them based on actual needs.

2. Working Principle of Hydraulic Solenoid Valve

The working principle of the solenoid valve is to use the magnetic field generated by the solenoid coil to control the movement of the valve core, thereby controlling the flow of liquid.

When the solenoid coil is energized, a magnetic field will be generated, which will make the valve core move, thereby changing the channel state between the valve core and the valve seat and controlling the flow of liquid.
When the solenoid coil is de-energized, the magnetic field disappears and the valve core returns to its original position, thereby closing or opening the liquid channel.

Hydraulic solenoid valve working principle diagram:



Working principle diagram and symbol of the three-position four-way directional valve
Figure 3: Working principle diagram of the three-position four-way directional valve.


1-Valve body; 2-Spring 3-Spring seat 4-Valve core 5-Coil 6-Armature 7-Sleeve 8-Casing 9-Solenoid valve connector

3. Functions of Hydraulic Solenoid Valve

Hydraulic solenoid valve is a device that controls the flow of liquid through electromagnetic force. It can achieve the start and stop, direction control, pressure control and other functions of various actuators in the hydraulic system (such as hydraulic cylinders, hydraulic motors, etc.). Specifically, solenoid valves mainly have the following functions in hydraulic systems:

(1) Start and stop control: The solenoid valve can achieve the start and stop control of various actuators in the hydraulic system by controlling the on and off of the solenoid coil, thereby realizing the motion control of mechanical equipment.

(2) Direction control: The solenoid valve can control the direction of liquid flow in the hydraulic system by changing the position of the internal valve core, thereby controlling the movement direction of the actuator.

(3) Pressure control: Some solenoid valves can also control the liquid pressure in the hydraulic system by adjusting the opening degree of the valve core, thereby ensuring that the system works within a certain pressure range.



solenoid-operated hydraulic directional control valves
Figure 4: Hydraulic directional control valves.

4. Hydraulic Solenoid Valve Types

Hydraulic solenoid valve refers to a component used to control liquid pressure, flow and direction in hydraulic transmission. Among hydraulic solenoid valves, those that control pressure are called pressure control valves, those that control flow are called flow control valves, and those that control the on, off and flow direction of fluid are called directional control valves.

These control valves have the following detailed classifications. Let’s take a look.

1. Directional control valves are divided into one-way valves and reversing valves according to their uses.

(1) One-way valve: It only allows fluid to flow through it in one direction in the pipeline, and cuts it off if it flows in the reverse direction.

(2) Directional valve: It changes the on-off relationship between different pipelines. According to the number of working positions of the valve core in the valve body, it is divided into two positions, three positions, etc. According to the number of controlled ports, it is divided into two-way, three-way, four-way, five-way, etc.

2. Pressure control valves can be divided into relief valves, pressure reducing valves and sequence valves according to their uses.

(1) Relief valve (overflow valve): It can control the hydraulic system to maintain a constant state when the set pressure is reached. The relief valve used for overload protection is called a safety valve. When a system failure occurs and the pressure rises to a limit value that may cause damage, the valve port will open to overflow to ensure system safety.



solenoid controlled relief valve bsg-03 sbsg-06
Figure 5: Solenoid controlled relief valve.


(2) Pressure reducing valve: It can control the branch circuit to obtain a stable oil pressure lower than that of the main circuit. According to the different pressure it controls, pressure reducing valves can be divided into fixed value type (the output pressure is a constant value), fixed difference type (the difference between input and output pressure is a fixed value) and fixed ratio type (the input and output pressure maintain a certain ratio).

(3) Sequence valve: After one actuator is activated, the other actuator is activated in sequence.

3. The flow control valve adjusts the flow rate by adjusting the orifice area between the valve core and the valve body and the local resistance it generates, thereby controlling the movement speed of the actuator. Flow control valves are divided into 5 types according to their uses.

(1) Speed control valve: It can keep the inlet and outlet pressure difference of the throttle valve at a constant value when the load pressure changes.

(2) Diverter valve: An equal-volume diverter valve can make two actuators of the same oil source obtain equal flow regardless of load size, and a proportional diverter valve can make two actuators obtain a proportionally distributed flow.

(3) Flow divider-combiner valve: It has the functions of diverting valve and collecting valve.

(4) Combiner valve: It makes the flow flow into it proportionally, and its function is opposite to that of the diverter valve.

(5) Throttle valve: After adjusting the orifice area, it can basically keep the movement speed of the actuator stable whose load pressure changes little and whose movement uniformity is not highly required.

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