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| Illustration 1 | g01101937 |
Cross section of the elevator pump (1) Drive shaft (2) Swashplate (3) Actuator piston (4) Retainer (5) Pistons (6) Pump control valve (7) Barrel (8) Port plate (9) Plug (10) Head (11) Spring (12) Bias piston (13) Bearing | |
When the engine is running, pump drive shaft (1) turns at engine speed. Shaft (1) rotates barrel (7) with nine pistons (5). The ends of the pistons are in the shape of a ball that fits into retainer (4). Retainer (4) slides on a thin film of oil on swashplate (2) that does not turn. swashplate (2) rests on bearings (13). This allows the swashplate to pivot in the pump housing. When swashplate (2) pivots, the angle of swashplate (2) changes and this causes a change of pump displacement.
The elevator pump has two bias pistons (12) with springs (11). Bias pistons (12) work against actuator piston (3) and bias pistons (12) keep the pump set toward the maximum angle. Actuator piston (3) is used to stroke the pump. Pump control valve (6) changes the pump displacement by regulating the pressure oil behind actuator piston (3), which is supplied by the pump discharge pressure. When pump control valve (6) allows oil pressure to actuator piston (3), actuator piston (3) moves bias pistons (12) and springs (11) in order to destroke the pump.
When pump drive shaft (1) turns barrel (7) and swashplate (2) is at some angle, pistons (5) are moved in and out on barrel (7) as barrel (7) follows the angle of swashplate (2). As pistons (5) are moved out of barrel (7), oil from the hydraulic tank flows through the pump inlet and port plate (8) and into the piston cylinder. As barrel (7) continues to turn, piston (5) is moved into barrel (7). Piston (5) then pushes the oil from the piston cylinder and through the port plate. The oil continues to flow out of the pump and to the elevator motor.
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| Illustration 2 | g01101955 |
Pump head (9) Plug (10) Head (14) Check valve (15) Spring | |
There is a check valve on each side of head (10). The check valve on the far side of pump head (10) is an inlet port for the discharge oil from the cushion-hitch. The inlet port for the discharge oil from the cushion-hitch connects with a passage that is common to the control valve for the elevator pump and check valve (14). Check valve (14) is in an inlet port for the discharge oil from the elevator pump. During normal pump operation, pump discharge pressure keeps check valve (14) open and the far check valve seated. Discharge oil from the elevator pump flows through the common passage to the control group for the elevator. When the elevator pump output pressure drops below 6900 kPa (1000 psi), the pump oil from the cushion-hitch opens the far check valve and seats check valve (14). The oil pressure from the cushion-hitch pump is 16000 kPa (2300 psi). The discharge oil from the cushion-hitch pump flows through the common passage to the control group for the elevator pump. This maintains the capability for full pump flow.
Pump Control Valve
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| Illustration 3 | g01101980 |
Cross section of the pump control valve (2) Swashplate (3) Actuator piston (6) Pump control valve (17) Spring (18) Pressure cutoff valve (19) Inlet port for signal pressure (20) Signal pressure valve (21) Spring (22) Chamber (23) Case drain passage (24) Spool (25) Lever arm (26) Lever arm cam (27) Shoe (28) Minimum stop (29) Spring (30) Spool (31) Chamber (32) Maximum stop (33) Inlet passage (34) Passage (35) Passage (36) Passages | |
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| Illustration 4 | g01102006 |
Left side of elevator pump (6) Pump control valve (18) Pressure cutoff valve (20) Signal pressure valve (32) Stop for maximum pump displacement | |
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| Illustration 5 | g01102012 |
Top rear of elevator pump (6) Pump control valve (26) Lever arm cam (28) Stop for minimum pump displacement (32) Stop for maximum pump displacement | |
Pump control valve (6) automatically keeps the pump flow at established rates for the speed of the elevator motor. The signal oil in chamber (22) and spring (21) cause spool (24) to move down. This allows pump discharge oil across the spool and bias spring (11) upstrokes the pump. The end of spool (24) rests on lever arm (25). Swashplate (2) contains spring (29) that holds shoe (27) up against the bottom of lever arm (25) .
As pump discharge oil is allowed into chamber (31), actuator piston (3) that is against swashplate (2) is moved to the right. This works against bias pistons (12) and springs (11) that try to keep the pump at a maximum angle. As the pump destrokes, shoe (27) slides to the right along lever arm (25). As shoe (27) slides to the right, spool (24) requires less force to be pushed down. The forces that are acting on spool (24) cause the discharge oil for the pump to be metered in chamber (31). Metering the oil in chamber (31) allows the pump to stroke to the needed output.
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| Illustration 6 | g01102017 |
Pump control valve and swashplate (2) Swashplate (3) Actuator piston (6) Pump control valve (18) Pressure cutoff valve (20) Signal pressure valve (24) Spool (25) Lever arm (26) Lever arm cam (27) Shoe | |
Signal pressure valve (20) changes the setting for upstroking the pump. Adjust valve (20) so that the pump will upstroke at a signal pressure of 600 ± 20 kPa (88 ± 3 psi) and discharge pressure is 6900 kPa (1000 psi).
Lever arm cam (26) changes the angle of lever arm (25). This will determine when the pump will end upstroking. As cam (26) is turned, shoe (27) follows the angle of cam (26) and shoe (27) changes the angle of lever arm (25). As the angle increases, less force is required on spool (24) to destroke the pump. Cam (26) should be set so that the pump will end stroking at 1600 ± 80 kPa (230 ± 12 psi) with the pump discharge pressure at 6900 kPa (1000 psi).
The cutoff pressure for the elevator pump is controlled by pressure cutoff valve (18). The maximum discharge pressure of the elevator pump is 36000 ± 700 kPa (5250 ± 102 psi). When the maximum pressure is reached, spool (30) moves up against spring (17). High pressure oil in passage (33) is metered across spool (30) and through passage (35). The oil continues to be metered through passage (34) and into chamber (31). High pressure oil shifts actuator piston (3) right and high pressure oil destrokes the pump to the minimum angle. High pressure oil in the system causes discharge oil to meter across spool (30) and the discharge oil will keep the pump at the minimum angle.
The stop for maximum pump displacement and adjustment (32) regulates the maximum flow output of the elevator pump. The stop for minimum pump displacement and adjustment (28) regulates the minimum flow output of the elevator pump.
Upstroking
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| Illustration 7 | g01102049 |
The cross section for the pump control valve in the upstroking position (2) Swashplate (3) Actuator piston (6) Pump control valve (17) Spring (18) Pressure cutoff valve (19) Inlet port for Signal pressure (20) Signal pressure valve (21) Spring (22) Chamber (23) Case drain passage (24) Spool (25) Lever arm (26) Lever arm cam (27) Shoe (28) Minimum stop (29) Spring (30) Spool (31) Chamber (32) Maximum stop (33) Inlet passage (34) Passage (35) Passages (36) Passages (AA) Pump discharge oil (BB) Case drain oil (CC) Signal oil | |
The pump upstrokes when a signal pressure from the main control valve is sent to signal inlet port (19). Signal pressure oil (CC) flows into chamber (22). Signal pressure oil (CC) and spring (21) cause spool (24) to move against lever arm (25) and shoe (27). The location of shoe (27) on lever arm (25) determines the amount of signal pressure oil that is needed to move spool (24) .
When spool (24) shifts, spool (24) will cause pressure oil from the pump to flow from chamber (31) and through passage (34). The oil continues to flow through passages (36). Oil (AA) continues to flow across spool (24) and into case drain passage (23). This vents pressure oil behind actuator piston (3). Bias pistons (12) and springs (11) keep a constant force on swashplate (2). Bias pistons (12) and springs (11) move swashplate (2) and actuator piston (3) to the left. This upstrokes the pump. Shoe (27) moves left along lever arm (25) and shoe (27) shifts spool (24). This stops oil in chamber (21) from venting. The forces on spool (24) are now balanced. Spool (24) shifts in order to meter the oil from chamber (31). The metering of oil in chamber (31) maintains a specific pump output.
Destroking
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| Illustration 8 | g01102062 |
Cross section of pump control valve in the upstroking position (2) Swashplate (3) Actuator piston (6) Pump control valve (17) Spring (18) Pressure cutoff valve (19) Inlet port for signal pressure (20) Signal pressure valve (21) Spring (22) Chamber (23) Case drain passage (24) Spool (25) Lever arm (26) Lever arm cam (27) Shoe (28) Minimum stop (29) Spring (30) Spool (31) Chamber (32) Maximum stop (33) Inlet passage (34) Passage (35) Passages (36) Passages (AA) Pump discharge oil (BB) Case drain oil (CC) Signal oil | |
The pump destrokes when the signal pressure that is sent from the main control valve to signal inlet port (19) is reduced or stopped. With no signal pressure oil to chamber (22), only spring (21) is working against the upward force of shoe (27) on lever arm (25) and spool (24). When spool (24) is shifted, pressure oil from the pump oil flows through passage (36) and passage (34). Pressure oil from the pump enters chamber (31) and pressure oil from the pump shifts actuator spool (3) to the right against the force of bias pistons (12) and springs (11). This destrokes the pump. Shoe (27) moves right along lever arm (25) and lever arm (25) causes spool (24) to shift stopping oil in passage (34) from entering chamber (31) .
Signal pressure in chamber (22) determines when the pump will stop destroking. The forces on spool (24) are now balanced. Spool (24) shifts in order to meter oil in chamber (31). The metering of oil in chamber (31) causes the pump to maintain a specific output.
At the start-up of the vehicle, the pump is at the maximum angle. Bias pistons (12) and springs (11) have pushed the actuator piston against maximum stop (32). With no signal pressure in chamber (22), spool (24) is shifted. Pump discharge pressure moves the actuator piston left until swashplate (2) is against minimum stop (28). The pump will remain at the minimum angle until a signal pressure in chamber (22) causes the pump to upstroke.