SUPPORT 5L9317 - Caterpillar

Charge Pump System
The hydrostatic drive system utilizes a charge pump in order to replenish oil that is lost due to normal leakage in the pump and in the motor.The system also contains the following components: charge valve, charge relief valve and shuttle spool. The charge relief valve connects to both sides of the drive loop. A shuttle spool inside the charge valve directs the flow from the charge pump to the low pressure side of the drive circuit.The low pressure side serves to supply the variable displacement pump. The shuttle spool also connects the low pressure side to the charge relief valve. The charge relief valve limits the pressure in the low pressure side of the drive loop. The charge relief valve limits the maximum pressure of the charge oil to approximately 1380 kPa (200 psi).The charge valve also contains the main relief valve for the high pressure side of the drive loop. Therefore, the charge valve may be called the charge and main relief valve. The main relief valve limits the maximum pressure in the high pressure side to approximately 38000 kPa (5500 psi).
Illustration 2 g00525345
Hydrostatic drive system schematic (A) Input power (B) Variable displacement pump (D) Fixed motor (E) Driven load (F) Charge and main relief valve (G) Charge relief valve (H) Oil cooler (J) Charge pumpThe schematic diagram shows an oil cooler that is positioned directly below the charge relief valve. During normal operation, the low pressure side of the drive loop does not require all the flow that is provided by the charge pump. Most of the oil from the low pressure side is sent through the charge relief valve