How to select the hydraulic directional control valve?

- Mar 04, 2021-

The selection of the directional control valve is based on the maximum pressure of the system and the actual flow through the valve, as well as the operation and installation methods of the valve.

hydraulic directional control valve

Following is the precautions for selecting the directional control valve:


(1) Determine the actual flow through the valve. At this time, pay attention to the relationship between the flow through the pipeline and the series and parallel of the oil circuit. When the oil circuit is connected in series, the flow of the system is the flow through the oil circuit; the oil circuit is connected in parallel and each When the oil circuits are working at the same time, the flow of the system is equal to the sum of the flow rates of each oil circuit.


(2) Pay attention to the difference in oil return between the two chambers of a single-piston rod hydraulic cylinder. The return oil flow when the piston is extended and retracted is different. The return oil flow of the rod-free cavity when retracted is different from the oil return flow of the rod cavity when extended. The ratio is equal to the ratio of the piston area of the two chambers.


The above two points 1, 2 emphasize that the actual flow through the valve (not according to the flow of the pump) should be used as one of the main parameters of the selection valve. If the actual flow rate through the valve is too small, the size (capacity) of the valve will be selected too small, and the partial pressure loss of the valve will be too large, resulting in excessive oil temperature and other consequences. In severe cases, the system will not work properly. In some hydraulic systems of pipe expanders, the electromagnetic reversing valve and hydraulic lock capacity are selected small, resulting in the partial pressure loss of each valve as high as 2.4MPa, which is far greater than their respective rated pressure loss of 0.3MPa, resulting in the system Can not meet the design requirements.


(3) Pay attention to the reasonable selection of the opening pressure of the one-way valve. The opening pressure of the one-way valve depends on the stiffness of its built-in spring. Generally speaking, in order to reduce the flow resistance loss, a check valve with a low opening pressure should be used as much as possible. On the other hand, for the control pressure necessary to maintain the electro-hydraulic directional valve, when the one-way valve is used as the back pressure valve, in order to ensure sufficient back pressure, a one-way valve with a high opening pressure should be selected.


(4) Pay attention to the reasonable selection of the pressure relief method of the hydraulic control check valve. When there is back pressure at the outlet of the hydraulic control check valve, the external discharge type should be selected, and the internal discharge type can be selected in other cases. For some hydraulic systems of lifting devices, due to poor design considerations, the external leakage hydraulic control one-way valve should be used, but the internal leakage type is selected, resulting in strong vibration and noise in the system.


In addition, pay special attention to whether there is a "negative pressure effect" in the opening pressure of the hydraulically controlled check valve in the locking circuit of the two-way hydraulic lock. This "negative pressure effect" will cause the jumping motion phenomenon and vibration of the actuator .


(5) It is necessary to correctly select the neutral function of the spool valve but also grasp the transition state function of the spool valve. The transition state function of the spool valve refers to the connection status of the spool valve oil circuit in the reversing transition position. Grasp the transition state function of the spool valve in order to know whether the oil circuit is completely blocked during the reversing transition of the valve, resulting in the phenomenon that the instantaneous pressure of the system is infinite. Designers generally pay attention to the neutral function of the spool valve, and often pay little attention to the transitional function of the spool valve, resulting in unexpected design errors.


(6) Pay attention to the application of electromagnetic directional valve and electro-hydraulic directional valve. Once the solenoid type (DC type, AC type, etc.) of the electromagnetic directional valve and the valve structure are determined, the valve commutation time is fixed; The liquid reversing valve can be adjusted to control the amount of oil passage.