ROD 9R8857 - Caterpillar

Illustration 1 g00531827
Pump Compartment (1) Swing filterThe charge pump is a gear type pump that is driven from the swing pump drive. The oil inlet to the pump is from the suction line of the main pump. The outlet is connected to the externally mounted swing circuit filter (1) and to the relief valve manifold.
Illustration 2 g00904918
Circuit for Swing Charge Pump (2) Pressure cutoff valve (3) Drive loop (4) Crossover relief valve (5) Filter (6) Swing charge pump (7) Poppet (8) Shuttle valve (9) Charge relief valve (10) Crossover relief valveThe charging pump relief valve (9) is connected to the output side of charging pump (6) past swing filter (5). Relief valve (9) is adjustable. The released oil is used to cool the swing pump. After the released oil passes through the pump case drain, the oil goes to the hydraulic tank.Crossover relief valve (4) and (10) and pressure cutoff valve (2) are connected to either side of the high pressure output (3) on the pump. The crossover relief valves are used to limit system pressure. The crossover relief valves also function as check valves. Pressure cutoff valve (2) returns oil from the pump outlet to the pump inlet through the high pressure spring and poppet valve (7) .Pressure cutoff valve (2) is an adjustable valve. Poppet (7) receives the high pressure through shuttle valve (8) from either side of the pump output. Poppet (7) shifts the cutoff spool in order to release the control pressure to the drain. Reduced control pressure reduces the pump swashplate angle in order to decrease the flow to a minimum while the pressure is kept at the maximum of the relief valve setting.The effective pressure on the swing motor is the difference between the high pressure side and low pressure side.Charge oil enters the drive loop that is at low pressure in order to act as makeup oil, when the swing pump is upstroked. The swing pump is shown in the upstroked position in illustration 2.Pressure in the low side of the drive loop is controlled by a flushing valve in the swing motor. The flushing valve continuously drains some oil from the low pressure side of the drive loop through the motor bearings to case drain. This action purges heat, debris and air from the drive loop.Shuttle valve (8) senses the highest pressure for the drive loop and this pressure is directed to pressure cutoff valve (2). Pressure cutoff valve (2) limits the maximum swing pressure.When pressure cutoff valve (2) opens, the pilot control pressure to the actuator piston for the swing pump is sent to the tank. The pump destrokes.