777F, 777G, and 785D OEM Off-Highway Truck/Tractors Water Delivery System Caterpillar

Illustration 1	g03665198
Rear of Engine (1) Charge pump (2) Cold-start relief valve

Charge pump (1) is located on the rear of the water delivery pump at the rear of the engine.

Charge pump (1) provides hydraulic oil to the variable displacement pump and closed loop hydraulic circuit. The charge pump is a gear pump. Excess fluid cools the variable displacement pump.

Cold-start relief valve group (2) is located near the charge pump outlet. This valve limits the pressure in the charge system when the hydraulic oil is cold.

The cold start relief valve relieves excessive charge pressure directly to the hydraulic oil tank. Normal charge pressure is regulated by the charge relief valve in the piston pump to 1902 kPa (276 psi). Charge pressure can be verified at the filter housing pressure port.