Working principle of single-head solenoid reversing valve

Single-head electromagnetic reversing valve is an automation basic component that controls the flow direction of fluid (liquid or gas) through electromagnetic force, and is widely used in hydraulic systems, pneumatic systems and industrial automation equipment. Its core function is to switch the valve core position through the on-off power of the solenoid, thereby changing the channel of the fluid and realizing the reversal, start-stop or pressure control of the fluid. The following are its detailed working principle and analysis of key components:

1. Basic structure composition

Single-head solenoid reversing valves are usually composed of the following core components:

Electromagnet: includes coil, core and armature. When powered on, electromagnetic force is generated to drive the valve core to move.

It is divided into two types: DC (DC) and AC (AC), and DC electromagnets respond faster and have lower noise.

Valve body: There are multiple flow channels (such as oil inlet P, working port A/B, and oil return port T) internally to form a fluid passage.

The material is usually high-strength cast iron or stainless steel to withstand high pressure and corrosive media.

Valve spool: cylindrical or conical structure, which can slide or rotate within the valve body, and change the flow channel communication mode through position changes.

The surface is precision ground and hard chrome-plated to reduce friction and wear.

Reset spring: Installed at one end of the valve core, and when power is off, the valve core returns to its initial position by relying on the spring force.

The spring stiffness needs to be matched with electromagnetic force to ensure rapid response and no vibration.

Seals: such as O-rings, lip-shaped seals to prevent fluid leakage, and the material must be adapted to the media type (such as nitrile rubber, fluoroelastomer).

2. Working principle (taking the two-position three-way valve as an example)

1. Initial status (power off)

The solenoid is not energized: The return spring presses the valve core to the limit position on the left (Figure 1).

Runner communication: The oil inlet P is disconnected from the working port A.

The working port A is in communication with the oil return port T, and the fluid flows back to the oil tank or atmosphere through the T port.

Application scenario: At this time, the actuator (such as cylinders, hydraulic cylinders) is in a retracted or stopped state.

2. Power-on status

Electromagnet energizes: The coil generates a magnetic field, attracting the armature to drive the valve core to move to the right, overcomes the spring force and compresses the spring (Figure 2).

Runner communication: The oil inlet P is in communication with the working port A, and high-pressure fluid enters the actuator to push the piston movement.

The working port A and the return port T are disconnected to prevent backflow of fluid.

Application scenario: The actuator extends out or starts to move.

3. Power off and reset

The electromagnetic field is powered off: the magnetic field disappears, and the spring force pushes the valve core back to the original position on the left.

Runner recovery: The working port A is connected again with the oil return port T, and the actuator retracts under the action of a load or a spring.

3. Key parameters and performance indicators

Diameter (DN): represents the nominal diameter of the valve body flow channel, which directly affects the flow rate (such as DN6, DN10), and needs to be matched according to system requirements.

Rated pressure: The maximum working pressure that the valve body can withstand (such as 16MPa, 31.5MPa), which may cause seal failure or deformation.

Response time: The time from power on to full movement of the valve core (usually 10-50ms), affecting the dynamic performance of the system.

Leakage: The maximum leakage allowed by the internal seal (such as ≤0.1ml/min), low leakage can improve system efficiency.

Working voltage: The rated voltage of the solenoid (such as DC24V, AC220V) must be matched with the control circuit.

4. Typical application scenarios

Hydraulic system: controls the expansion and contraction direction of the hydraulic cylinder, such as the mold opening and closing of the injection molding machine, and the ejection mechanism of the die-casting machine.

Pressure adjustment is achieved with the overflow valve, such as machine tool clamping device.

Pneumatic system: controls the reciprocating movement of the cylinder, such as grabbing and handling mechanical arms on an automated production line.

Used for pneumatic logic control, such as pneumatic valve switches, safety door locks.

Industrial automation: linking with PLC and sensors to realize process automation (such as packaging machine sealing and printing machine ink circuit switching).

Control the hydraulic/pneumatic actuator action in robot joint drive.