1) The role of overflow valve
The relief valve uses the imported oil pressure to balance the spring force to achieve pressure control.
There are four main functions of relief valve for hydraulic excavators. 1) In the hydraulic system of fixed pump (gear pump), it is used to overflow the excess oil back to the tank to maintain the pressure of the hydraulic system constant (approximately constant).
2) In the variable pump hydraulic system, the overflow is only opened when the pressure exceeds a certain preset pressure value, so that the system pressure will no longer rise, and play a safety protection role. At this time, the overflow valve is often called a safety valve.
3) In the system, it is used to protect actuators (such as cylinders) or structural parts from being damaged under strong external forces. In this case, the overflow valve is called an overload valve.
4) As a pressure limiting valve to buffer and limit the pressure of the rotating mechanism.
3) The working principle of the relief valve
①Pump pressure PP rises
②When it exceeds 21.6MP
③The pump pressure pushes the poppet (2) to overcome the force of the spring (1) and push it upwards
④The small hole of the plunger (3) (only φ0.5) starts to have oil flow
⑤The plunger (3) is pushed up due to the pressure difference between the front and back (the lower part is larger, the upper part becomes smaller)
⑥Pressure oil return to tank
⑦The pump pressure drops to 21.6
