In the hydraulic system of agricultural machinery, the pressure valve is a type of component that is used more often. Sudden failure of the pressure valve will directly affect the normal operation of the mechanical equipment. This paper divides the failure cause of the pressure valve and gives an example of the testing method of the pressure valve. 1. Common causes of failure (1) The hydraulic valve body and valve body wear continuously during use, which causes the part size, shape and surface quality to change. (2) Balance springs, valve plugs, and valve seats in hydraulic valves work under long-term varying loads, resulting in fatigue and cracks that cause springs, breaks, or valve seat seal surfaces to flake off and damage. (3) Residual residual stress during the processing of hydraulic valve parts and the external load stress during use exceeds the yield strength of the part material and the part is deformed. (4) The hydraulic oil is mixed with too much water or acidic material. After a long time, the parts in the hydraulic valve are corroded and the accuracy thereof is lost. (5) The radial force between the valve core and the valve sleeve is not balanced, and finally the valve core is pressed against the inner wall of the valve sleeve. (6) When the hydraulic valve was manufactured or repaired, it did not meet the specified technical requirements; or the parts were not well kept, rust occurred, and dirt was mixed. 2. Examples of test methods Pressure valves include relief valves, pressure relief valves, and sequence valves. This article uses the relief valve as an example to illustrate the test items and test methods for pressure valves. Pressure valve testing can be performed on a dedicated test bench or on a comprehensive test bench. (1) Pressure regulation range and pressure stability test. Adjust the adjustment handwheel of the test valve, from full open to fully closed and then fully open, and see from the pressure gauge the pressure rise and fall and the pressure adjustment range. The pointer of the pressure gauge should rise and fall steadily. The pressure regulation range should meet the specified pressure regulation range. At the highest pressure, the pressure pulsation value must not exceed the specified value. (2) Test of internal leakage. Adjust the adjustment handwheel of the valve to the fully closed position, adjust the overflow relief valve as the highest pressure of the tested valve, and then adjust the adjustment handwheel of the test valve so that the overflow outlet of the test valve measures the internal leakage. (3) unloading pressure test. The remote control port of the relief valve is connected to the tank so that the test valve passes the test flow and the inlet and outlet pressures of the relief valve are measured. The difference is the unloading pressure of the tested valve. (4) Pressure loss test. Adjust the adjustment handwheel of the test valve to fully release, and make the test valve pass the test flow, and measure the inlet and outlet port pressure of the overflow valve by the pressure gauge. The difference is the pressure loss of the test valve. (5) Open and close characteristics test. Close the overflow relief valve, adjust the test valve to the highest pressure, adjust the overflow relief valve to gradually reduce the pressure of the system, and measure the overflow of the test valve when the test valve is closed to the closing pressure. Adjust overflow relief valve, from the beginning of the test valve does not overflow, so that the system gradually increased pressure, when it rose to the test valve opening pressure, measured by the valve overflow.
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