CAM 0065092 - Caterpillar

Function
The relief valve is mounted to the scraper control valve. This valve protects the scraper pump and the bowl, apron, and ejector circuits from excessive pressures during operating positions. This valve also functions as a flow control valve that permits two return speeds of the ejector.Relief Valve Operation
Pump flow is sensed on dump valve (10). Pump flow is also sensed through a small passage (2), in the relief valve body, on stem (6). As the pressure of the pump flow increases, stem (6) is moved to stop (8), compressing the spring. As the oil pressure increases to the pressure setting of the relief valve, the pilot valve (9) is unseated and dump valve (10) moves against the force of its spring. This allows full pump flow to be directed to return passage (11) and to the tank.Adding shims (7) increases the relief valve pressure setting; removing shims decreases the pressure setting.
MAIN PRESSURE RELIEF VALVE SCHEMATIC
1. Passage (senses pressure in the common passage in the control valve). 2. Passage (senses pump flow pressure). 3. Stem valve. 4. Passage. 5. Passage. 6. Stem. 7. Shims. 8. Stop. 9. Pilot valve. 10. Dump valve. 11. Return chamber. 12. Pump flow chamber.The pressure setting of the relief valve is approximately 2000 psi (140.6 kg/cm2) (2710 kPa).Flow Control Operation
The relief valve acts as a flow control valve when the ejector control valve spool is in RETURN (flow control) position or, when the bowl or apron valve spools are between HOLD and LOWER positions, delivering oil through throttling slots only.In these positions, pump flow is directed to the common passage, in the control valve, through throttling slots in the valve spool which restricts the pump flow. Passage (1) in the relief valve body senses the pressure in the common passage. The oil flows through passages (1) and (4) and moves stem valve (3). This closes passage (2) and passage (1) to stem (6). Normally, the pressure in the common passage is less than the pressure of the oil in chamber (12). Therefore, stem (6) is not forced to stop (8) and the pressure required to unseat pilot valve (9) is lower. The high pressure oil acting on dump valve (10) now moves it up and some of the pump oil is directed to return passage (11) and to the tank. If the GPM from the pump increases, there is a greater pressure differential across the spool and the dump valve moves up further, allowing more oil to be directed to return passage (11) and to the tank. In this manner the relief valve controls the flow in the common passage. The relief valve will now open when pump oil pressure is approximately 1200 psi (84.4 kg/cm2) (1630 kPa).Testing and Adjusting
Before installing or removing test equipment: Lower the bowl and apron. Move the ejector forward. Shut off the engine and shift the scraper control levers through all positions to neutralize the pressure. Loosen the hydraulic tank filler cap to relieve tank pressure. Tighten the