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| Illustration 1 | g01063582 |
(1) Piston pump group (2) Pilot port (one per rotating group) (3) Maximum angle stop screw (one per rotating group) (4) Shaft (5) Pilot port (one per rotating group) (6) Cross over relief valves and makeup valves (two per rotating group) (7) Charge pressure relief valve (8) Adjustment for the pump null (one per rotating group) | |
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| Illustration 2 | g01063583 |
Typical Example of one piston pump (4) Shaft (9) Control arm for the swashplate (10) Actuator piston (11) Actuator (12) Piston (13) Swashplate (14) Retraction plate (15) Cylinder barrel (16) Valve plate (A) Passage to port (B) Passage to port | |
The Piston Pump (hydrostatic system) operates in a closed loop system. The Piston Pump (hydrostatic system) is a variable displacement piston pump with a maximum displacement of 46 cc/rev (2.81 in3/rev). The Piston Pump (hydrostatic system) consists of two separate pumps. The two pumps are bolted together. The pump is driven from the engine flywheel by a coupling that is splined to the shaft (4) .
The following main components of the Piston Pump (hydrostatic system) are located internally: input shaft (4), control arms (9) and actuator piston (10) swashplates (13) , pistons (12) , retraction plates (14) , Cylinder barrel (15) and Valve plate (16) .
The pilot ports (2) and (5) are used to control the angle of the swashplate (13). The angle of the swashplate and the engine rpm controls the output of the pump. The pilot ports are connected to the resolver network on the pilot valve ( hydrostatic).
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| Illustration 3 | g01063585 |
(10) Actuator piston (17) Spring collar (18) Spring collar (19) Spring | |
The shaft (4) for the pumps consists of two shafts that are splined together between the two pumps. Each swashplate can operate independently. Pump 1 supplies the left hand piston motor and pump 2 supplies the right hand piston motor. For the following example of the operation of the pump, pump 2 will be used. Pump 1 will operate in the same manner.
When the operator moves the pilot valve in order to move the machine forward, pilot oil flows out of the pilot valve and into pilot port (2). This causes the actuator piston (10) to move to the right in illustration 3. The movement of the piston to the right causes actuator (11) to move the control arm (9). The movement of the control arm increases the angle of the swashplate (13). Half of the pistons in the cylinder barrel (15) pull oil into each cylinder as the pistons rotate around the swashplate. The oil enters the pump through port (A). The other half of the pistons push oil out of each cylinder. The oil exits the pump through the valve plate (16) and out of port (B). As the angle of the swashplate increases the output of the pump increases.
When the operator moves the pilot valve in order to move the machine backward, pilot oil flows out of the pilot valve and into pilot port (5). This causes the actuator piston (10) to move to the left in illustration 3. The movement of the piston to the left causes the actuator (11) to move the control arm (9). The movement of the control arm increases the angle of the swashplate (13). Half of the pistons in the cylinder barrel (15) pull oil into each cylinder as the pistons rotate around the swashplate. The oil enters the pump through port (B). The other half of the pistons push oil out of each cylinder. The oil exits the pump through the valve plate (16) and out of port (A). As the angle of the swashplate increases the output of the pump increases.
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| Illustration 4 | g01063589 |
(20) Speed sensing valve | |
The speed sensing valve (20) senses the change in the flow of oil from the gear pump as the engine speed changes. An orifice in the speed sensing valve creates a pressure differential within the valve. The valve uses the pressure differential to provide more flow or less flow to the pilot valve in order to control the piston pump. An increase in the pressure differential will cause more oil to flow to the pilot valve. The pressure of the speed sensing valve to the pilot valve fluctuates from 900 ± 200 kPa (130 ± 30 psi) to 3200 ± 100 kPa (465 ± 15 psi). The solenoid for the pilot valve must be energized in order for the pilot valve to be functional.