PUMP GP-GOV & FUEL INJ 7C4300 - Caterpillar

Illustration 6 g00660952
Schematic of the Elevator Circuit in the NEUTRAL Position (1) Gear pump (elevator) (2) Piston pump (elevator) (3) Relief valve (gear pump) (4) Charge filter (6) Piston motor (elevator) (8) Relief valve (piston motor) (11) Flush valve for the motor (12) Flush valve for the motor (13) Bypass valve (charge filter) (14) Orifice for the pressure override valve (15) Pressure override valve (16) Pump control valve (17) Pump control piston (18) Crossover relief valve for piston pump (elevator) (19) Makeup check valve (20) Bleed orifice (21) Pressure override resolver valve (AA) Active spool position (BB) Pressure oil for the tank (CC) Charge pressure oil (DD) Pump pressure oil (EE) Reduced pressure oilWhen the engine is started and the elevator control lever is in the NEUTRAL position, oil is drawn from the bottom of the hydraulic oil tank to the inlet port of gear pump (1). The gear pump will send the charge oil to charge filter (4). All of the flow from the gear pump must pass through the element before the oil can enter the remainder of the system. Restrictions in the filter element can cause the pressure at the inlet side of the filter to increase. If the pressure at the inlet side is too high, bypass valve (13) will open. The valve will direct oil around the charge filter.Oil flows from charge filter (4) through an orifice to pressure override valve (15). When the system pressure remains below the pressure setting of the pressure override valve, oil will flow to pump control valve (16). In the NEUTRAL position, the pump control valve will vent both ends of pump control piston (17) to the hydraulic tank. When there is no supply of control oil pressure, the pump control piston will return to the NEUTRAL position. With the piston pump in NEUTRAL, The flow of oil is not sent from the piston pump to piston motor (6) .Flow is directed to relief valve (3). During the neutral condition, the system pressure in the closed loop will be controlled by the relief valve. Excess flow of oil is then sent to the hydraulic tank.The charge oil will flow to crossover relief valves (18) and makeup check valves (19) downstream of pressure override valve (15). The crossover relief valves will remain closed. The makeup valves will meter a small amount of oil to both sides of the closed loop. The makeup valves direct the oil in order to make up lost oil due to leakage and normal lubrication.The swashplate will remain at a zero angle, which will produce no pump output. Gear pump (1) will maintain a positive equal pressure in both sides of the closed loop. The pressure in the closed loop will prevent piston motors (6) from drifting during neutral. The pin that is located in the flushing valve of both motors will remain in the CLOSED position. When the pin is in the CLOSED position, cooling oil