01
The O symbol is:
P indicates the oil inlet, T indicates the oil return port, and A and B indicate the working oil port.
Structural features:
In the middle, the oil ports are completely closed and the oil does not circulate.
Functional characteristics:
1. The inlet and outlet ports of the working device are all closed. The working mechanism can be fixed at any position and it can not be moved. Even if there is an external force, the working mechanism cannot be moved or rotated. Therefore, it cannot be used in a mechanism with hand crank.
2, from the stop to start relatively stable, because the working mechanism back into the oil chamber is full of oil, can play a buffering role, when the pressure oil to push the working mechanism to start moving, due to the impact of oil resistance and its speed will not be too fast, system The inertia of motion caused by hydraulic shock during movement.
3, the oil pump can not be unloaded.
4, high precision reversing position.
02
The H symbol is
Structural features:
In the middle position, all ports are fully open and there is no oil pressure in the system.
Functional characteristics:
1. The oil inlet P, the oil return port T and the working oil port A, B are all connected, so that the working machine is in a floating state and can be moved under the action of an external force and can be used in a mechanism with a hand crank.
2, the hydraulic pump can be unloaded.
3, from the stop to start impact. Because the oil in the oil return chamber has returned to the tank when the working mechanism is stopped, no oil acts as a buffer. The oil port communicates when braking, so the brake is more stable than O type.
4. For single-lever double-acting cylinders, the pistons are not fully stopped due to the different effective area of ​​the piston on both sides.
03
The type M symbol is
Structural features:
In the middle 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 institutions with a hand device.
4, from the stop to start more stable.
5. The inertia of the motion caused by the brake causes a large hydraulic shock.
6, can be used for oil pump unloading and hydraulic cylinder lock hydraulic circuit.
04
The Y type symbol is
Structural features:
In the middle position, the oil inlet P is closed, and the working oil ports A and B communicate with the oil return port T.
Functional characteristics:
1. Because the working oil ports A and B communicate with the oil return port T, the working mechanism is in a floating state and can move with the action of external force and can be used in a mechanism with a hand crank.
2, from the stop to start some shock, from the static to start the impact, braking performance between 0 and H type.
3, the oil pump can not be unloaded.
05
The P symbol is
Structural features:
In the middle position, the oil return port T is closed, and the oil inlet P communicates with the working oil ports A and B.
Functional characteristics:
1. For double-rod double-acting cylinders of equal diameter, the hydraulic pressures at both ends of the piston are balanced with each other and the working mechanism can be stopped. It can also be used in institutions with hand-operated devices. However, for single rods or double-bar double-acting cylinders with different diameters, the working mechanism cannot be in a stationary state and constitute a differential circuit.
2. It is relatively stable from stop to start. When the brake is on, both chambers pass pressure oil, so the brake is stable.
3, the oil pump can not be unloaded.
4. The change of reversing position is smaller than that of H-type and it is widely used.
06
The type N symbol is
Structural features:
In the neutral position, the inlet port P and the working port B are closed, and the working port A and the return port T communicate with each other.
Functional characteristics:
1, the pump can not be unloaded.
2, can move in a single direction under the action of external forces.
07
U-shaped symbols are
Structural features:
A, B working oil port connected, inlet port P, oil return port T closed.
Functional characteristics:
1. Because the working oil ports A and B are connected, the working device is in a floating state and can be moved under the action of external force, and can be used in a mechanism with a hand-operated device.
2, from the stop to start more stable.
3, when braking is relatively stable.
4, the pump can not be unloaded.
08
The K symbol is
Structural features:
In the neutral position, the oil inlet P is in communication with the working oil port A and the oil return port T, and the other working oil port B is closed.
Functional characteristics:
1, the oil pump can be unloaded.
2. The performance is different when commutating in both directions.
09
The J type symbol is
Structural features:
The oil inlet P and the working oil port A are closed, and the other working oil port B is connected to the oil return port T.
Functional characteristics:
1, the pump can not be unloaded.
2. The performance is different when commutating in both directions.
10
The C symbol is
Structural features:
The oil inlet P communicates with the working oil port A, and the other working oil port B communicates with the oil return port T.
Functional characteristics:
The pump can not be unloaded; it is relatively stable from stop to start, and there is a large impact during braking.
Example analysis
1. Use the median function of the slide valve as an unloading circuit to achieve energy saving. When the positional function of the slide valve is H, K or M, the three-position reversing valve is in the neutral position, the oil output by the pump is directly returned to the tank to form an unloading circuit, which can make the pump idle or have a small output power. Exercise under conditions to achieve energy savings. This method is relatively simple, but it is not suitable for a system where one pump drives two or more actuators.
2. Use the median function of the slide valve as a brake circuit or locking circuit. In order to stop the moving working mechanism at any desired position and prevent it from moving after being stopped due to external influences, a brake circuit may be used. The simplest method is to use a reversing valve for braking. For example, a spool valve with M-type or O-type reversing valve can cut off its oil return path and stop the actuator quickly when it returns to neutral position.
3, using H-type, Y-type commutation to achieve the float. For example, when the hydraulic crane's swing mechanism rotates under the load, if the brake is too rapid, the inertial force will produce a large hydraulic shock. Therefore, the spool valve function is often used as an H-type or Y-type reversing valve when the reversing valve When returning to the neutral position, the swing motor is in a floating state, and then braked with the foot to stop it smoothly. When the M-type and H-type 4-position reversing valves are in the H-position, that is, in the floating position, the material can be scooped down or the site can be leveled. The bucket can be raised and lowered with the height of the ground, that is, floating; When the system suddenly stops working, the bucket can still be put down smoothly. A reversing valve with a Y-spool function is used on the reversing valve of the crawler excavator traveling motor, which can make the traveling motor in a floating state during the excavation work not bear the braking load.
4. The selection of the median function of the reversing valve spool valve has a very important impact on the vibration performance of the roller compactor hydraulic system. Using the H type three-position four-way valve, when the spool valve is in the neutral position, the four oil ports P, T, A, and B communicate with each other and constitute the same channel. Due to the rotating inertia of the exciter, the vibrating wheel will generate aftershock, resulting in indentation on the surface of the compacted ply, but this will affect the compaction effect of the base layer for the vibratory roller of the roadbed. Not much, but it also reduces the hydraulic impact of the system. For vibratory roller compactor, it is required to stop vibration or amplitude during compaction operation. The exciter can quickly stop rotation in the time of 1.5-1.7s to avoid momentary residual vibration and compaction. Indentations appear on the surface and affect compaction quality. The M-type three-position four-way reversing valve is often used. When the spool valve is in the neutral position, the two working ports A and B are cut off, which can generate a large back pressure, prompting the motor to rapidly stop against the exciter inertia moment. Rotation, in order to avoid indentation in the real-time pressure on the road surface, but will cause a very high instantaneous pressure peak in the motor circuit, increase the damage rate of the motor and other related components. Therefore, two relief valves are usually installed on the A and B ports of the reversing valve to protect the system.
In short, when selecting the reversing valve, it is necessary to select the appropriate median function according to the working characteristics of the working mechanism.
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