OPERATIONAL PERFORMANCE TEST / Component Test OVERLOAD RELIEF VALVE SET PRES- SURE Summary: 1. The circuit pressure must be increased by apply- ing an external force while blocking the return cir- cuit from the control valve. This measuring method is hazardous and the results obtained with this method are unreliable. 2. The oil flow rate used to set the overload relief pressure is far less than that used to set the main relief pressure. Therefore, measuring the overload pressure in the main circuit by increasing the main relief set pressure more than the overload valve set-pressure is not a proper method.
In addition, in case a main relief valve designed to leak a small quantity of oil before reliving is used, its pre-leaking start pressure must be increased more than the overload relief valve set pressure. However, the pre-leaking start pressure is not al- ways increased more than the overload relief valve set-pressure as the adjustable upper limit of the main relief valve set-pressure is provided. Accordingly, the overload relief valve assembly should be removed from the machine and checked on a specified test stand at a correct oil flow rate. Some overload relief valves come in contact with the control valve body to block the oil passage.
When this type of overload relief valve is checked, the control valve body must be precisely finished as the test unit. Provide one control valve other than that on the machine as a test kit. 3. If the overload relief valve performance must be checked on the machine, however, measure the main relief pressure while releasing each front function respective to the measuring overload re- lief valve. And, assume that the overload relief valve is functioning correctly if the obtained main relief pressure is within the specified value range. Measure the main pressure of the front functions by using Dr. ZX as follows: Preparation: 1. Stop the engine. 2.
Push the air bleed valve on top of the hydraulic oil tank and release any remaining pressure. 3. Remove the plug from pressure check port of main pump delivery port. Install adapter (ST 6069), hose (ST 6943) and pressure gauge (ST 6941). : 6 mm 4. Connect Dr.ZX and select the monitoring function. Start the engine. Confirm that no oil leakage is observed at the pressure gauge connection. 5. Maintain the hydraulic oil temperature at 50 ± 5 ° C (122 ± 41 ° F). T4-5-15