CABLE AS 7Y8294 - Caterpillar

Illustration 1 g00538009
Main Relief Valve (1) Shims (2) Spring (3) Pilot valve (4) Spring (5) Dump valve (6) Chamber (7) Passage to hydraulic tank (8) Orifice (9) Passage with system oil pressure
Illustration 2 g00538011
Location of the main relief valveThe main relief valve is attached to the winch motor control valve. The relief valve is a pilot type valve. The pilot valve limits the pressure in the system to approximately 18250 kPa (2650 psi).Pump oil enters the relief valve housing through passage (9). The oil then flows through orifice (8) in dump valve (5), into chamber (6) and against pilot valve (3) .When the pressure of the oil is lower than the setting of the relief valve, dump valve (5) is held closed by spring (4) and pilot valve (3) is held closed by spring (2) .When the oil pressure comes up to the relief valve setting, pilot valve (3) opens. When the valve opens the oil in chamber (6) flows back to the hydraulic tank through passage (7). The oil flow through passage (7) is faster than the oil flow through orifice (8). This causes the pressure in chamber (6) to decrease. The pressure of the pump oil moves dump valve (5) upward against the force of spring (4). This opens passage (9) to tank passage (7) and pump flow is sent to the tank.The pressure setting of the relief valve can be changed by either an increase or a decrease in the force of spring (2) that keeps pilot valve (3) closed. The force of the spring can be changed by the addition or removal of shims (1) .See Systems Operation, Testing and Adjusting, "Pressure Tests of the Relief Valves".