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| Illustration 1 | g00297397 |
(1) Steering piston pump (2) Pressure compensator valve (3) Pump drive shaft (4) Swashplate (5) Outlet opening (6) Piston (7) Barrel (8) Inlet opening (9) Actuator piston (10) Spring | |
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| Illustration 2 | g00297398 |
(2) Pressure compensator valve (11) Spool (12) Spring (13) Shims (14) Passage from steering piston pump outlet (15) Passage to actuator piston (16) Passages to steering pump case drain line | |
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| Illustration 3 | g00301290 |
(1) Steering piston pump (2) Pressure compensator valve (17) Pump drive | |
Steering piston pump (1) is a variable displacement axial piston pump. The steering piston pump is fastened to pump drive (17). Pump drive (17) is located on the inside right hand frame rail near the torque converter. Steering piston pump (1) only operates when the engine is running.
When the engine is started, the pump drive (17) turns pump drive shaft (3) and barrel (7) with nine pistons (6). The ends of pistons (6) connect to a retraction plate and slippers. The retraction plate and slippers turn with barrel (7). The retraction plate and slippers are against swashplate (4). Swashplate (4) does not turn. Swashplate (4) can pivot in order to change the angle.
When pump drive shaft (3) and barrel (7) turn with swashplate (4) at the maximum angle position, pistons (6) move in and out of barrel (7) as the slippers follow the angle of the swashplate. As pistons (6) move out of barrel (7), oil is pulled from the steering hydraulic tank through inlet opening (8) and into the piston cylinder in the barrel. As barrel (7) turns farther, pistons (6) are moved back into barrel (7). This pushes the oil from the piston cylinder in barrel (7). The oil flows through the outlet opening (5) and into the steering hydraulic system.
When the pressure of the oil from the steering piston pump is less than the pressure setting of the pressure compensator valve (2), oil from outlet opening (5) that is in passage (14) will not move spool (11). The pressure of the oil from the steering piston pump will increase as the steering accumulators are charged.
The pressure of the oil from the steering piston pump will increase until the oil in outlet opening (5) and passage (14) has more force on the spool (11) than the force of spring (12). This will move the spool (11). The pressure of the oil that can move the spool (11) is the pressure setting of the pressure compensator valve (2) .
When the spool (11) is moved, the oil in passage (14) now flows through passage (15) to actuator piston (9) in the steering piston pump (1). The force of the oil from passage (15) moves actuator piston (9) which moves the swashplate (4) to a minimum angle.
When demand for oil from the steering accumulators is low, pump drive shaft (3) and barrel (7) turn while swashplate (4) is at a minimum angle position. The pistons (6) have very little movement. This movement of the pistons (6) is enough to supply oil for lubrication and leakage. Because of normal leakage in the steering hydraulic system, the pressure in the steering accumulators will gradually decrease.
When the oil pressure in the steering accumulators decreases to a pressure that is below the force of spring (12), there will be a decrease in the oil pressure at passage (14). The spring (12) will move the spool (11). This blocks passage (15). No oil will flow to actuator piston (9). Spring (10) moves the swashplate (4) to a maximum angle position and the steering piston pump output is back to maximum flow. Oil in the actuator piston (9) is drained through passages (16).