SHAFT AS-PUMP 4P8891 - Caterpillar

Illustration 1 g02953276
Compartment for the main control valve (return circuit) (1) Main control valve (2) Inlet line to hydraulic oil cooler (3) Slow return check valve (4) Makeup line (makeup oil to swing motor)
Illustration 2 g02089274
Slow return check valve and bypass check valve (2) Inlet line to hydraulic oil cooler (3) Slow return check valve (5) Return line (return flow to return filter) (6) Return port (7) Check valve (8) Return line to bypass check valve (9) Bypass check valve (10) Hydraulic oil coolerThe return oil flow through slow return check valve (7) is divided into two flow paths. A portion of the oil flows through inlet line (2) to the hydraulic oil cooler and the remainder of the return oil flows through bypass check valve (9) .When the temperature of the return oil in inlet line (2) is very low, the viscosity of the oil is high. The flow resistance of the return oil in inlet line (2) is high. Thus, the pressure of the return oil is high.
Illustration 3 g02092454
(5) Return line (11) Return filter (12) Hydraulic tankAs a result of the high pressure of the return oil, bypass check valve (9) opens. Most of the return oil flows through bypass check valve (9), return line (5) , return filter (11) to hydraulic tank (12). The remainder of the oil flows through inlet line (2) to the hydraulic oil cooler. Since a small amount of the return oil flows to the oil cooler, the temperature of the oil increases. As the oil temperature increases, the return oil pressure decreases. Bypass check valve (9) begins to close. A greater portion of the return oil flows to the hydraulic oil cooler. Bypass check valve (9) maintains the hydraulic oil at the optimum operating temperature.