PLATE 3904927 - Caterpillar

Illustration 1 g00847520
Main control valve compartment (return circuit)
(5) Makeup line (makeup oil to swing motor)
(10) Main control valve
(17) Slow return check valve
(29) Inlet line to hydraulic oil cooler (18)
Illustration 2 g01234594
Slow return check valve and bypass check valve
(5) Makeup line (makeup oil to swing motor)
(16) Return line
(17) Slow return check valve
(24) Bypass check valve
(28) Check valve
(29) Inlet line to hydraulic oil cooler (18)
(30) Return line to bypass check valve
(33) Return line (return flow to return filter) The return oil flow through slow return check valve (17) is divided into two flow paths. A portion of the oil flows through inlet line (29) to the hydraulic oil cooler and the remainder of the return oil flows through bypass check valve (24).When the temperature of the return oil in inlet line (29) is very low, the viscosity of the oil is high. The flow resistance of the return oil in inlet line (29) is high. Thus, the pressure of the return oil is high.
Illustration 3 g00849905
(19) Return filter
(25) Hydraulic tank
(33) Return line As a result of the high pressure of the return oil, bypass check valve (24) opens. Most of the return oil flows through bypass check valve (24), return line (33) and return filter (19) to hydraulic tank (25). The remainder of the oil flows through inlet line (29) 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 (24) begins to close. A greater portion of the return oil flows to the hydraulic oil cooler. Bypass check valve (24) maintains the hydraulic oil at the optimum operating temperature.