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| Illustration 1 | g00278695 |
Inside of right hand frame rail (1) Steering piston pump (2) Pressure compensator valve | |
Steering piston pump (1) is a pressure compensating variable displacement axial piston pump. The steering piston pump is fastened to the pump drive. The pump drive is located on the inside right hand frame rail near the rear of the engine. Steering piston pump (1) only operates when the engine is running.
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| Illustration 2 | g00522231 |
Section view of the steering piston pump (3) Inlet opening (4) Piston (5) Actuator piston (6) Swashplate piston (7) Barrel (8) Swashplate (9) Pump drive shaft | |
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| Illustration 3 | g00522233 |
(2) Pressure compensator valve (10) Low pressure cut-in valve (11) High pressure cutoff valve | |
When the engine is started, the pump drive turns pump drive shaft (9) and barrel (7) with nine pistons (4). The ends of pistons (4) connect to a retraction plate and slippers. The retraction plate and slippers turn with barrel (7). The retraction plate and slippers are against swashplate (8). Swashplate (8) does not turn. Swashplate (8) can pivot in order to change the angle.
When pump drive shaft (9) and barrel (7) turn with swashplate (8) at the maximum swashplate angle, pistons (4) move in and out of barrel (7) as the slippers follow the angle of the swashplate. When the swashplate (8) is at the maximum angle, the steering piston pump is at maximum flow. Since the steering piston pump is driven by the engine, the engine rpm also affects pump output flow. As pistons (4) move out of barrel (7), oil is pulled from the steering hydraulic tank through inlet opening (3) and into the piston cylinder in the barrel. As barrel (7) continues to turn, pistons (4) are moved back into barrel (7). This pushes the oil from the piston cylinder in barrel (7). The oil flows through the outlet opening and into the steering hydraulic system.
The pump oil flows at maximum pressure through the steering solenoid and relief valve to the accumulators. The steering solenoid and relief valve also routes oil to the accumulator charging valve and the steering control valve. The oil that flows to the accumulator charging valve is used as signal pressure. The accumulator charging valve uses this signal pressure to monitor the pressure of the accumulators. While the accumulators are filling, pump oil travels through a signal line that is between the accumulator charging valve and pressure compensator valve (2). This signal line to low pressure cut-in valve (10) causes the oil in actuator piston (5) to drain to the tank. The spring on swashplate piston (6) holds swashplate (8) at the maximum position.
Pump pressure will be on both sides of pressure compensator valve (2), but the pressure compensator valve will remain at maximum flow. Pistons (4) travel in and out of barrel (7) and maximum flow is provided through the outlet port. Since the steering piston pump is driven by the engine, the engine rpm also affects pump output flow.
When the steering accumulators are full, the signal pressure to the accumulator charging valve will reach the cutoff pressure. When the cutoff pressure is reached, the oil that flows through the signal line to pressure compensator valve (2) is drained into the steering hydraulic tank. The spool in low pressure cut-in valve (10) shifts. Oil pressure is sent to actuator piston (5). The oil pressure overcomes the spring pressure of swashplate piston (6). This moves swashplate (8) in order to destroke the pump to a low pressure standby condition. Pump output pressure is equal to the setting of low pressure cut-in valve (10) .
In the NO STEER position, demand for oil from the accumulators is low. The pump operates at a minimum swashplate angle in order to supply oil for lubrication and for leakage in the steering piston pump. The normal leakage of the steering metering pump is supplied by the accumulator pressure. This leakage is normal. This leakage will cause the pressure in the steering accumulators to gradually decrease to the cut-in pressure. The steering piston pump will cycle frequently due to this leakage.