GEAR GP 2862865 - Caterpillar

Bulldozer Hydraulic System
The hydraulic system for the bulldozer and the hydraulic system for the steering are two complete hydraulic systems. The pump for the two systems is a vane-type with two pump sections. The pump section at the shaft end is for the steering and the pump section at the cover end is for the bulldozer. The two systems use oil from the same hydraulic tank.The bulldozer control valve in the hydraulic tank gets oil directly from the pump. The pump oil goes through the control valve, through the oil filter and into the hydraulic tank when the control lever (and the control valve) is in the HOLD position.
CONTROL LEVER IN HOLD POSITIONWith the control valve in the HOLD position, the oil flow is stopped to and from the head end and the rod end of the bulldozer cylinder and the bulldozer will not move.Move the control lever from the HOLD position to the RAISE position to let the pump oil in the control valve go to the rod end of the cylinder. The bulldozer will lift when the oil moves the rod farther into the cylinder. As the rod moves into the cylinder, the piston on the rod forces the oil out of the head end of the cylinder, through the control valve and through the oil filter into the hydraulic tank.
BULLDOZER CYLINDERThe other positions for the control lever are LOWER and FLOAT. A spring in the control valve will move the valve spool and the control lever from either the RAISE or LOWER position to the HOLD position. When the valve spool is in the FLOAT position, balls, held in the detent by springs, keep the valve spool in the FLOAT position. Force is needed to move the lever (and the valve spool) out of the FLOAT position.Control Valve
Hold Position
The oil from the pump goes into the control valve through inlet (7). With valve spool (2) in HOLD position (H) the pump oil goes around the valve spool and through passages in the control valve to outlet (5). The oil from outlet (5) goes through the oil filter and into the hydraulic tank.The HOLD position of the valve spool keeps the oil in passages (3) and (4) from going to or from the bulldozer cylinder and the bulldozer will not move. The valve spool also keeps oil in the spring chamber of check valve (6) and the pump oil can not open the check valve.
SCHEMATIC OF CONTROL VALVE IN HOLD POSITION
1. Relief valve. 2. Valve spool. 3. Passage to the head end of the bulldozer cylinder. 4. Passage to the rod end of the bulldozer cylinder. 5. Outlet to the filter and tank. 6. Check valve. 7. Inlet from the hydraulic oil pump. F. FLOAT position. H. HOLD position. L. LOWER position. R. RAISE position.Lower Position
With valve spool (2) held in the LOWER position, the pump oil in the control valve becomes higher and opens check valve (6). The oil goes through the open check valve