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

(1) Relief 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 will open and overflow to ensure the safety of the system.

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

(3) Sequence valve: After one actuator (such as a hydraulic cylinder, hydraulic motor, etc.) is activated, other actuators are activated in sequence. The pressure generated by the oil pump first pushes the movement of hydraulic cylinder 1, and at the same time acts on area A through the oil inlet of the sequence valve. When the movement of hydraulic cylinder 1 is complete, the pressure rises, and the upward thrust acting on area A is greater than the setting of the spring. After the value is reached, the valve core rises to connect the oil inlet and the oil outlet, causing the hydraulic cylinder 2 to move.

Flow control valve: Adjust 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) Throttle valve: After adjusting the throttle area, the movement speed of the actuator that has little change in load pressure and low requirements for motion uniformity can be basically kept stable.

(2) Speed regulating valve: It can keep the inlet and outlet pressure difference of the throttle valve at a constant value when the load pressure changes. In this way, after the throttle area is set, no matter how the load pressure changes, the speed regulating valve can maintain the flow rate through the throttle valve unchanged, thereby stabilizing the movement speed of the actuator.

(3) Diverter valve: Regardless of the size of the load, an equal-volume diverter valve or a synchronization valve can make two actuators of the same oil source obtain equal flow; a proportional diverter valve can obtain a proportional distribution of flow.

(4) Collector valve: Its function is opposite to that of the diverter valve, so that the flow flowing into the collector valve is proportionally distributed.

(5) Diverting and collecting valve: It has the functions of diverting valve and collecting valve.

Directional control valves are divided into check valves and reversing valves according to their uses.

One-way valve: Only allows fluid to be connected in one direction in the pipeline, and is cut off in the reverse direction.

Directional valve: Change 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-way, three-way, etc.; according to the number of controlled channels, it is divided into two-way, three-way, four-way, etc. Five-way, etc.; according to the valve core driving mode, it is divided into manual, motorized, electric, hydraulic, etc. When the spool is in the neutral position, all oil ports are cut off and the actuator does not move; when the spool moves to the right position, P and A are connected, and B and O are connected; when the spool is moved to the left position, P and B are connected , A and O are connected. In this way, the actuator can move forward and reversely.

Several considerations when selecting hydraulic control valves:

Various specifications and models of hydraulic control valves can be based on the maximum pressure of the system and the actual flow rate of the valve (checked from the working condition diagram and system diagram) and take into account the valve control characteristics, stability, oil port size, overall dimensions, installation and connection methods, and control methods. etc., select from product samples or catalogues. Things to note when selecting various types of hydraulic control valves are as follows:

1. Actual flow rate of hydraulic control valve:

The actual flow rate of the hydraulic control valve is related to the series and parallel connection of the oil circuits: the flow rate of the series oil circuits is equal; the flow rate of the parallel oil circuits working at the same time is equal to the sum of the flow rates of each oil circuit. In addition, when using a single piston rod hydraulic cylinder system, it should be noted that the oil return flow rate is different when the piston extends and retracts: the ratio of the oil return flow rate of the rodless cavity when retracting to the rod cavity oil return flow rate when extending, and the ratio of the area of the two chambers equal.

2. Rated pressure and rated flow of hydraulic valve:

The rated pressure and rated flow of each hydraulic control valve should generally be close to the operating pressure and flow. For systems with higher reliability requirements, the rated pressure of the valve should be much higher than its operating pressure. If the rated pressure and rated flow rate are less than the operating pressure and flow rate, it will easily cause hydraulic clamping and hydraulic power and have a negative impact on the working quality of the valve. The flow rate of the sequence valve and pressure reducing valve in the system should not be much less than the rated flow rate, otherwise it is easy to produce Vibration or other unstable phenomena. For flow valves, attention should be paid to their minimum stable flow.

3. Hydraulic control valve installation and connection method:

The valve installation and connection method has a decisive influence on the subsequent design of the structural type of the hydraulic device. When selecting a hydraulic valve, you should be aware of the integration method of the hydraulic control device. For example, the plate-type connection hydraulic valve is used, because the valve can be installed on the oil circuit board or oil circuit block, which facilitates system integration and rational design of the hydraulic device. In addition, when replacing the hydraulic valve, there is no need to disassemble the oil pipe, making installation and maintenance more convenient; using stacked valves, It is necessary to study the pressure and flow and superimpose the valve series type spectrum for selection, etc.

4. Selection of directional control valve:

For ordinary check valves with a simple structure, the main attention should be paid to the reasonable selection of its opening pressure: a lower opening pressure can reduce the resistance loss of the liquid flow check valve; when a one-way valve is used as a back pressure valve, its opening pressure is higher to ensure Enough back pressure. For hydraulic control valves, in order to avoid causing abnormal vibration and noise in the system, attention should also be paid to the reasonable selection of its pressure relief method: when there is back pressure at the outlet of the hydraulic control check valve, the external leakage type should be selected, and in other cases, the internal leakage type can be selected.

For reversing valves, attention should be paid to rationally selecting the operating type from manual, mechanical, electromagnetic, electro-hydraulic and other types based on meeting the system's automation and operating cycle requirements. Correctly select the neutral performance of the slide valve type reversing valve and grasp its transitional quasi-state performance. Hydraulic lock (double hydraulic control one-way valve) is used to lock the hydraulic actuator system. "H" or "Y" shaped neutral function spool type reversing valve should be selected so that when the reversing valve is in the neutral position, the two hydraulic actuators The control cavity of the control check valve is all connected to the oil tank, ensuring reliable reset of the hydraulic control check valve and good locking state of the hydraulic actuator. The selected spool-type reversing valve has a neutral function and a reversing transition position, and the oil circuit should not be completely blocked. Otherwise, the instantaneous pressure of the system will be infinite and cause accidents such as pipeline blasting.