COVER 4W1072 - Caterpillar

Illustration 1 g03012960
Hoist hydraulic system schematic
(1) Hoist cylinder
(2) Hoist cylinder rod end pressure tap
(3) Hoist cylinder head end pressure tap
(4) Line to brake oil cooling
(5) Hoist control valve
(6) Brake oil cooler relief valve
(7) Low-pressure relief valve
(8) High-pressure relief valve
(9) Screen
(10) Stem
(11) Make up valve
(12) Hoist proportioning solenoid for raise
(13) Centering springs
(14) Stem
(15) Hoist proportioning solenoid for SNUB, FLOAT, and LOWER
(16) Pilot system pressure tap
(17) Line from the electric drive brake release pump
(18) Hydraulic tank breather
(19) Lines to the steering metering pump and the steering lockout valve
(20) Implement and steering solenoid valve
(21) Automatic lubrication system connection port
(22) Check valve
(23) Line to the parking brake control valve
(24) Line from the parking brake control valve
(25) Hydraulic oil level sensor
(26) Check valve
(27) Hoist and brake cooling section of the gear pump
(28) Screen
(29) Pilot oil filters
(30) Brake and pilot section of the gear pump
(31) Hydraulic tank
(32) Pilot oil pressure reducing valve
Illustration 2 g03022316
Location of hoist control valve
(6) Brake oil cooler relief valve
(7) Low-pressure relief valve
(8) High-pressure relief valve
(12) Hoist proportioning solenoid for RAISE (not shown)
(15) Hoist proportioning solenoid for SNUB, FLOAT, and LOWER
(33) Actuators Oil flows from brake and pilot pump section (30) of the gear pump through check valve (26) to pilot oil pressure reducing valve (32). Pilot oil pressure reducing valve (32) maintains a constant pilot oil pressure to the parking brake, and to the steering and hydraulic pilot circuits. From the pilot oil pressure reducing valve, the oil flows through pilot oil filter (29). This oil is then divided.Some of the pilot oil flows to the parking brake circuit through check valve (22) and line (23). The rest of the pilot oil flows to the implement and steering solenoid valve (20).When implement and steering solenoid valve (20) is energized, pilot oil flows through lines (19) to steering metering pump and steering lockout valve. Also pilot oil flows to hoist proportioning solenoid for lower (15) and hoist proportioning solenoid for raise (12).This oil is used as pilot oil for hoist proportioning solenoid (15) and hoist proportioning solenoid (12). Pilot oil is always present at both ends of directional spool (14).The hoist proportioning solenoids are used to drain the pilot oil from the ends of directional spool (14), which then allows the spool to move.Oil flows from brake cooling and hoist pump section (27) of the gear pump to hoist control valve (5). The hoist control valve will send pump oil to one of two locations. When the dump body is being raised or lowered, the hoist cylinders receive the oil. If the hoist is not being used, the oil flows to the oil cooling system for the brakes.Brake oil cooler relief valve (6) limits the pressure in the brake oil cooling system. Brake oil cooler relief valve (6) will return oil to hydraulic tank (31), when brake oil cooling pressure is too high.Low-pressure relief valve (7) limits the pressure to the rod end of hoist cylinders (1) when the body is being lowered. Low-pressure relief valve (7) will open when the pressure becomes