Closed circuit operation
Hydraulic lines connect the main ports of the pump to the main ports of the motor. Fluid flows in either
direction from the pump to the motor and back. Either of the hydraulic lines can be under high pressure.
The position of pump swashplate determines which line is high pressure as well as the direction of flow.
Case drain and heat exchanger
Both the pump and motor must drain fluid. A case drain line achieves this. The line connects to the pump
or motor at the top-most drain port in order to maintain an adequate fluid level in the components. Fluid
cooling demands may require a heat exchanger with a bypass valve to cool the case drain fluid before it
returns to the reservoir.
Pump features
Charge pump
The charge pump is necessary to supply fluid to maintain positive pressure in the system loop, to provide
pressure to operate the control system, and to make up for internal leakage and loop flushing flow. To
prevent damage to the transmission, the pump must maintain the specified charge pressure under all
conditions of operation.
Service Manual
Series 42 Axial Piston Closed Circuit Pumps
Functional Description
10 520L0638 • Rev 0300 • July 2015
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