Knowledge points to master about hydraulic Directional valve

Author: Hou

Apr. 08, 2025

21 0 0

1. Directional valve action

The directional control valve is a directional control valve with more than two flow forms and more than two oil ports. It is a valve that realizes communication, shut-off and reversing of hydraulic oil flow, pressure unloading and sequential action control.

2. Working principle of Directional valve

Reverse valve is through the spool in the valve body to do axial movement, so that the corresponding oil communication or disconnection. A plurality of undercut grooves are arranged in the valve body, the undercut grooves are connected with the outside through a pore passage, and a plurality of steps are arranged on the valve core. The reversing valve is realized by changing the communication relationship between the step on the spool and the undercut groove on the valve body to switch the oil circuit.

3. Control mode of Directional valve

(1) Motorized Directional valve, also known as stroke valve

(2) electromagnetic directional valve, electromagnetic directional valve is the use of electromagnetic attraction to control the direction of valve core transposition control valve

(3) Electro-hydraulic directional valve, electro-hydraulic directional valve is composed of electromagnetic directional valve and hydraulic directional valve composite valve

(4) Manual reversing valve, manual reversing valve is a directional control valve with a hand-pushed lever to control the valve core transposition.

4."Position" and "On" of Directional valve

Many non-professional people on the reversing valve "bit" and "pass" concept is not very clear, in fact, very simple, can be understood directly from the literal meaning: "bit" means the working position of the reversing valve, there are several working conditions there are several "bit","pass" means the number of holes connected with the outside. Such as three-position four-way valve, there are three working positions, four oil ports.

Bits-expressed in squares, a few bits are squares
2, pass--↑ No, no. ---
Arrows and blockages symbol and a square have several intersections, that is, several passes
3, P, A, B, T have fixed orientation
P---Oil inlet, T(O)---Oil return
A, B-Working oil port connected with actuator
4. Control mode and return spring-W are drawn on both sides of the square.
Two-position valve, one compartment by spring.
5. Normal position (In the schematic diagram, the oil circuit should be connected in the normal position)
Three-position valve, one in the middle.

5. The neutral function of Directional valve and its application

The neutral function refers to the valve spool in the middle position or the original position of the valve in the form of communication of the oil port, reflecting the control function of the valve. The use of different forms of spool valve will directly affect the operating conditions of the actuator.

O-type neutral Directional valve symbol is:

P represents the oil inlet, T represents the oil return port, A and B represent the working oil port.

Structural characteristics and working principle:

In the neutral position, all oil ports are completely closed and oil does not circulate.

Functional characteristics:

1. The inlet and return oil ports of the working device are closed, and the working mechanism can be fixed at any position, and even if there is an external force, the working mechanism cannot be moved or rotated, so it cannot be used for the mechanism with manual operation.

2, from stop to start is relatively stable, because the working mechanism oil return chamber is full of oil, can play a buffer role, when the pressure oil to push the working mechanism to start moving, due to the influence of oil resistance and make its speed not too fast, braking motion inertia caused by hydraulic shock is large.

3, the oil pump can not be unloaded.

4. High accuracy of reversing position.

Application examples:

H-type neutral reversing valve symbol is

Structural characteristics:

In the neutral position, all oil ports are fully open, and there is no oil pressure in the system.

Functional characteristics:

1. The oil inlet P and the oil return port T are all communicated with the working oil ports A and B, so that the working mechanism is in a floating state and can move under the action of external force, which can be used for the mechanism with manual operation.

2. The hydraulic pump can be unloaded.

3. There is impact from stop to start. Because when the working mechanism stops, the oil in the oil return chamber has already flowed back to the oil tank, and there is no oil to buffer. When braking, the oil ports communicate, so the braking is more stable than O type.

4, for single-rod double-acting cylinder, because the effective action area on both sides of the piston is not equal, so with this function of the spool valve can not completely ensure that the piston is in a stopped state.

Application examples:

The symbol of the M-type neutral reversing valve is

Structural characteristics:

In the neutral position, the working oil ports A and B are closed, and the oil inlet P and the oil return port T are directly connected.

Functional characteristics:

1. Since the working oil ports A and B are closed, the working mechanism can remain stationary.

2. The hydraulic pump can be unloaded.

3, can not be used for the mechanism with hand device.

4. It is relatively stable from stop to start.

5, braking motion inertia caused by large hydraulic impact.

6, can be used for oil pump unloading and hydraulic cylinder locking hydraulic circuit.

Application examples:

Y-type neutral reversing valve symbol is

Structural characteristics:

In the neutral position, the oil inlet P is closed, and the working oil ports A and B are communicated with the oil return port T.

Functional characteristics:

1. Because the working oil ports A and B are communicated with the oil return port T, the working mechanism is in a floating state and can move with the action of external force, which can be used for the mechanism with manual operation.

2, from stop to start some impact, from rest to start the impact, braking performance between 0 and H type.

3. The oil pump cannot be unloaded.

The symbol of P type neutral reversing valve is

Structural characteristics:

In the neutral position, the oil return port T is closed, and the oil inlet P is communicated with the working oil ports A and B.

Functional characteristics:

For double-rod double-acting cylinders of equal diameter, the hydraulic forces on both ends of the piston are balanced with each other, and the working mechanism can stop. It can also be used for mechanisms with hand-operated devices. However, for single-rod or double-rod double-acting cylinders with different diameters, the working mechanism cannot be in a static state and form a differential circuit.

2. From stop to start, it is relatively stable. When braking, both chambers of the cylinder are connected with pressure oil, so the braking is stable.

3. The oil pump cannot be unloaded.

4, commutation position change is smaller than H type, widely used.

Application examples:

N-type neutral reversing valve symbol is

Structural characteristics:

In the neutral position, the inlet P and the working port B are closed, and the working port A and the return port T are communicated.

Functional characteristics:

1. The oil pump cannot be unloaded.

2, can move in one direction under the action of external force.

The symbol of U type neutral reversing valve is

Structural characteristics:

Working oil ports A and B are connected, oil inlet P and oil return T are closed.

Functional characteristics:

1. Since the working oil ports A and B are connected, the working device is in a floating state and can move under the action of external force. It can be used for mechanisms with hand shaking devices.

2. It is relatively stable from stop to start.

3, braking is also relatively stable.

4. The oil pump cannot be unloaded.

The symbol of the K-type neutral reversing valve is