Overflow valve, also known as safety valve, is a kind of hydraulic pressure control valve, in the hydraulic equipment mainly set pressure overflow function, voltage regulator, system unloading and safety protection function.

When the system pressure is greater than the pressure set by the overflow valve, the hydraulic oil flows back through the overflow valve to the tank.

Take the simplest direct-action overflow valve as an example, p for system pressure, spring compression has pressure, to the right pressure, when the system pressure is too high, will be the spring top, thereby overflow from T, hydraulic oil from t flow back to the tank. The main overflow valve is installed at the upper and lower ends of the main control valve, one on top and the next. The valve sets the maximum pressure for the entire hydraulic system to work. When the system pressure exceeds the main overflow valve set pressure, the main overflow valve open back to the fuel tank oil flow will overflow back to the fuel tank to protect the entire hydraulic system, to avoid excessive pressure on the circuit.

The overflow valve has two-level set pressure, when the pilot pressure is off, for the first set of pressure 355kg/cm2, when the pilot pressure is on, for the two-level set pressure 380kg/cm2.

One of the reasons for the slow operation of the whole car is that the whole car pressure can not be established, the pressure is low, and the main overflow valve equipment is likely to lead to the failure of the culprit. The main overflow valve is located on the distributor valve body of a safety valve, its role is to limit the entire hydraulic system of the highest pressure to protect the entire system is not damaged, if the valve in the spring break or adjust the pressure is too low, will cause the entire system pressure is too low,

Because the main overflow valve pressure relief so that the entire hydraulic system can not establish the normal operation of the equipment required pressure, then the main pump pressure oil can not promote the normal operation of the components, there will be a whole vehicle slow and even no action phenomenon, at this time should be checked to replace or adjust the main overflow valve. The overflow valve of excavator is easy to produce high frequency noise, which is mainly caused by the unsteady performance of the pilot valve, which is the noise caused by the high frequency oscillation of the front chamber pressure of the pilot valve.

The main reasons are: (1) Oil mixed with air in the pilot valve before the formation of cavitation in the cavity phenomenon and caused by high-frequency noise.

At this time, should be timely exhaust air and prevent the outside air re-enter.

(2) needle valve in the course of use due to frequent opening and excessive wear, so that the needle valve cone and valve seat can not be closed, resulting in the pilot flow instability, pressure fluctuations caused by noise, should be repaired or replaced in time. (3) The pilot valve because of spring fatigue deformation caused by its pressure regulating function is unstable, make the pressure fluctuation and cause noise, the spring should be replaced at this time.