How to choose the hydraulic pressure switch?

- Mar 04, 2021-

How to choose pressure switch in hydraulic system? What problems should be paid attention to when using pressure switches? 

pressure switch

The main basis for selecting a pressure switch is usually based on the maximum pressure of the hydraulic system and the flow rate through the valve, and the corresponding specifications (pressure level and diameter) are selected from the product samples.


1) The difference between the lowest working pressure and the highest working pressure at which the pressure relay can send an electrical signal is called the pressure regulating range, and the pressure relay should also be selected within this pressure regulating range.


2) The structure of the valve can be selected according to the system performance requirements. For example, a direct-acting pressure valve can be selected for a low-pressure system, and a pilot-operated pressure valve should be used for a medium-high pressure system. According to the space location, pipeline layout, etc., select the pressure valve of plate type, tube type or superposition type connection.


3) Each performance index of the pressure valve has an impact on the hydraulic system. The pressure valve can be selected according to the performance curve on the sample according to the requirements of the system.


4) For all kinds of pressure valves connected to the control oil circuit, because the actual flow through is very small, it can be selected according to the minimum rated flow specification of the valve to make the hydraulic device compact.


Common failures of pressure switch are sensitivity reduction and damage to the micro switch, which are caused by the radial clamping of the valve core and push rod or the excessive idle stroke of the micro switch.


1) When the valve core or push rod is clamped radially, the friction force increases. This resistance is opposite to the movement direction of the spool and the push rod. One direction helps to adjust the spring force to increase the oil pressure, and the other direction helps the oil pressure overcome the elastic force and reduce the oil pressure. The sensitivity of the pressure switch is reduced.


2) If the drain cavity of the pressure relay is not directly connected to the fuel tank, the sensitivity will be reduced due to the excessive back pressure of the drain port.


3) The micro switch part of the differential pressure relay and the drain cavity are separated by a rubber membrane, so when the oil inlet cavity and the drain cavity are reversed, the pressure oil will break through the rubber diaphragm and enter the micro switch part, thereby damaging it Micro Switch.


4) Since the pressure regulating spring cavity and the drain cavity are connected, there is no sealing device at the adjustment screw, so when the drain pressure is too high, external leakage occurs at the adjustment screw, so the drain cavity must be directly connected to the oil tank.


5) In use, due to the deformation of the micro switch bracket or the looseness of the zero adjustable part, the minimum idle stroke of the micro switch that has been adjusted or guaranteed after assembly will increase and the sensitivity will be reduced.


6) In the throttle speed regulating circuit with dead stop iron positioning, the installation position of the pressure relay should be on the same side as the flow control valve and close to the hydraulic cylinder. The pressure in the oil inlet cavity of the oil inlet throttle speed control circuit changes with the load. When the working part hits the dead stop and stops moving, its pressure rises to the relief valve setting pressure, and this pressure is used as the command signal for the control sequence action . In the oil return throttle speed control circuit, the pressure of the oil return chamber changes with the load, and the pressure will drop to zero after the working part hits the dead stopper, so the zero pressure is taken to send a command signal.