PLATE-WEAR 4J9778 - Caterpillar

Illustration 1 g01322074
(1) Relief Valve (Charge Pressure) (2) Modulating valvesRelief valve (1) (charge pressure) is located on the left side of the transmission near the top of modulating valves (2) .The relief valve (charge pressure) regulates the hydraulic oil pressure in the transmission. The relief valve limits the maximum charge pressure to the adjusted setting.
Illustration 2 g00886302
Schematic for Relief Valve (Charge Pressure) (1) Relief valve (charge pressure) (2) Line to modulating valves (transmission) (3) Oil cooler bypass valve (4) Transmission lube relief valve (5) Charge pressure oil (6) Hydraulic oil cooler (7) Line to transmission clutches (lube oil)If the engine is running, the charge pump is pumping oil.The charge pump provides filtered oil to the relief valve (charge pressure). The hydraulic oil is regulated by the relief valve at a maximum pressure of 2100 kPa (305 psi). The charge oil is used in the modulating valves.Excess flow from the relief valve (charge pressure) will be diverted to the following components:
Hydraulic oil cooler
Oil cooler bypass valve
Relief valve (transmission lube)
Transmission lubrication circuit
SumpValve Operation
The relief valve (charge pressure) works as a pilot operated/spring return valve. This valve works independently from all electrical control systems.
Illustration 3 g00886311
Relief Valve (Charge Pressure) (8) Chamber (9) Orifice (10) Ball (11) Spring (12) Chamber (13) Spool (14) Spring (15) Screw (16) Chamber (17) OrificeHydraulic oil from the charge pump flows into relief valve (1) (charge pressure) at chamber (8). Charge oil enters orifice (9) and presses against ball (10) .The ball will push spring (11) as the pressure increases. The ball will overcome the spring pressure. This will allow oil to flow to chamber (12) .Oil pressure in chamber (12) will push spool (13) to the right against spring (14) .Note: Adjust screw (15) in order to obtain the 2100 kPa (305 psi) pressure setting.The spool will open a passage for oil to flow from chamber (8) to chamber (16). Oil flows through chamber (16) to the hydraulic oil cooler. As the spool moves further to the right, the amount of oil that is diverted to the hydraulic oil cooler will increase.When the pressure in chamber (12) equals the pressure that is exerted by spring (14), the movement of the spool to the right will stop.The pressure in chamber (8) should be 2100 kPa (305 psi).When the charge pump is stopped, or the oil flow from the charge pump is insufficient, the spool will move to the left. This movement will continue if the flow and pressure is not sufficient enough to maintain a pressure of 2100 kPa (305 psi) in chamber (8) .When all flow and pressure is stopped, spring (14) will push the spool all the way to the left side of the relief valve. Spring (11) will push ball (10) to the right. This will keep pilot oil from entering chamber (12) .Orifice (17) will allow the oil that is trapped in chamber (12) to be released. This will allow the spring to push the spool all the way to the left.