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| Illustration 1 | g01305520 |
Implement Pump and Compensator (Engine Off) (1) Pressure Compensator Spool (2) Flow Compensator Spool (3) Load Sensing Signal (4) Margin Spring (5) Cutoff Spring (6) Case Drain Passage (7) Pump Output (8) Large Actuator (9) Swashplate (10) Drive Shaft (11) Small Actuator and Bias Spring (12) Piston and Barrel Assembly (13) Signal Passage to Large Actuator (BB) Cutaway Section (CC) Component Surface (FF) Activated Component (GG) Tank Pressure | |
The implement hydraulic pump is a variable displacement slipper type piston pump. The pump is load sensing, pressure compensated, and flow compensated. The output of the pump is dependent upon the system demands that are sensed by the compensator valve.
The pump compensator valve has the following components:
Pressure Compensator Spool (1) and Cutoff Spring (5) - When the output pressure of the pump is great enough to overcome the force of the cutoff spring, the pressure compensator spool shifts upward. This allows oil into the large actuator in order to destroke the pump.
Flow Compensator Spool (2) - The load sensing signal and the margin spring apply pressure on the top of the spool. The pump output pressure acts on the bottom of the spool. The flow compensator spool shifts upward in order to regulate pressure in the large actuator.
Margin Spring (4) - When the engine is OFF, the flow compensator spool does not have oil pressure on either end. The margin spring pushes the flow compensator spool downward in order to keep the large actuator open to the case drain line. When the engine is started, the swashplate will be held at the maximum angle by the bias spring.
The implement hydraulic pump has the following components:
Large Actuator (8) - When oil pressure increases behind the large actuator piston, the piston will overcome the force of the small actuator and bias spring. This causes the angle of the swashplate to be reduced.
Swashplate (9) - The displacement of the pump is controlled by the angle of the swashplate. When the swashplate is at a maximum angle, the pistons move the maximum volume of oil in and out of the rotating barrel.
Drive Shaft (10) - The rotation of the pump is clockwise when the pump is viewed from the drive end. The piston and barrel assembly is splined to the drive shaft.
Small Actuator and Bias Spring (11) - When oil pressure is behind the small actuator piston, the angle of the swashplate will be increased. If there is no pressure behind the large actuator piston, the bias spring will hold the swashplate at the maximum angle.
Piston and Barrel Assembly (12) - The barrel contains nine pistons. The piston and barrel assembly rotates whenever the engine is running. The pistons move oil into the barrel and out of the barrel.
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| Illustration 2 | g01305535 |
Compensator Valve (Engine Off) (1) Pressure Compensator Spool (2) Flow Compensator Spool (3) Load Sensing Signal (4) Margin Spring (5) Cutoff Spring (6) Case Drain Passage (7) Pump Output (13) Signal Passage to Large Actuator (14) Adjustment Screw (15) Orifice (BB) Cutaway Section (CC) Component Surface (FF) Activated Component (GG) Tank Pressure | |
The compensator valve is bolted to the implement pump. The compensator valve contains two spools: pressure compensator spool (1) and flow compensator spool (2) .
Load sensing signal (3) is sent from the signal resolver network. This signal is the highest signal that is commanded by any of the control valves. The signal is not the sum of the signals that are commanded by all of the control valves. This signal represents the single greatest load that is being placed on the hydraulic system.
The flow that is supplied by the hydraulic pump is the amount that is required in order to keep the supply pressure at the pressure of load sensing signal (3) plus the margin pressure.
Margin pressure is equal to the spring force value of margin spring (4). Margin pressure is adjusted by turning adjustment screw (14) on flow compensator spool (2). See the Testing and Adjusting section in this manual for the correct procedure and pressures.
Pressure compensator spool (1) limits the maximum system pressure. When the pressure of pump output (7) is high enough to overcome the force of cutoff spring (5), pressure compensator spool (1) shifts to the right. As a result, the cutoff pressure is equal to the forces of spring (5). High pressure oil is allowed into signal passage (13) to the large actuator. The angle of the swashplate is reduced and the pump destrokes.
Orifice (15) is in the signal passage to the large actuator piston. Orifice (15) regulates the response rate of the large actuator piston by creating a consistent leak path.
Note: Orifice (15) must be installed with the slot for the screwdriver parallel to the spool bores.
Low Pressure Standby
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| Illustration 3 | g01305563 |
Implement Pump and Compensator (Low Pressure Standby) (1) Pressure Compensator Spool (2) Flow Compensator Spool (3) Load Sensing Signal (4) Margin Spring (5) Cutoff Spring (6) Case Drain Passage (7) Pump Output (8) Large Actuator (9) Swashplate (10) Drive Shaft (11) Small Actuator and Bias Spring (12) Piston and Barrel Assembly (13) Signal Passage to Large Actuator (BB) Cutaway Section (CC) Component Surface (FF) Activated Component (GG) Tank Pressure (KK) First Pressure Reduction | |
Low pressure standby occurs when the engine is running and the control levers are in HOLD. The only flow demands on the system are compensation for leakage and the production of pilot oil. Bias spring (11) holds swashplate (9) at the maximum angle before the engine is started. The pump output pressure is felt at the bottoms of both spools of the compensator valve.
As pump output pressure increases, flow compensator spool (2) is pushed upward against the force of margin spring (4). When the pump supply pressure becomes greater than the force of the margin spring, flow compensator spool (2) moves up. Pump output oil flows into large actuator (8). The force of small actuator and bias spring (11) is overcome and swashplate (9) moves toward the minimum angle until equilibrium is reached.
The pump is at low pressure standby. Flow compensator spool (2) continues to meter oil to large actuator (8) in order to balance the forces at the top and at the bottom of the spool.
Note: Low pressure standby is not adjustable. Low pressure standby will vary between machines. Low pressure standby will also vary in the same pump as leakage increases. As leakage increases, the pump will upstroke slightly in order to compensate for the leakage.
Upstroke
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| Illustration 4 | g01305916 |
Implement Pump and Compensator (Upstroke) (1) Pressure Compensator Spool (2) Flow Compensator Spool (3) Load Sensing Signal (4) Margin Spring (5) Cutoff Spring (6) Case Drain Passage (7) Pump Output (8) Large Actuator (9) Swashplate (10) Drive Shaft (11) Small Actuator and Bias Spring (12) Piston and Barrel Assembly (13) Signal Passage to Large Actuator (16) Reduced Pressure (BB) Cutaway Section (CC) Component Surface (FF) Activated Component (GG) Tank Pressure (JJ) High Pressure (PP) Signal Pressure | |
When an implement hydraulic circuit is activated and that circuit requires flow, pump output pressure (7) falls. The force of margin spring (4) and load sensing signal (3) becomes greater than the pump output pressure. Flow compensator spool (2) shifts downward.
When the spool shifts downward, the flow of oil to large actuator (8) is blocked. Oil that is in the chamber of large actuator (8) is vented to the case drain across flow compensator spool (2). The small actuator and bias spring (11) moves swashplate (9) to a greater angle.
The pump now produces more flow. This condition is known as "upstroking".
The pump may upstroke under the following conditions:
- An implement is initially activated from low pressure standby or multiple implements are activated.
- A main control spool in a hydraulic control valve is in a position that requires the pump to compensate for system leakage.
- A main control spool in a hydraulic control valve is moved to a position that increases system demand.
- The demand from the implements remains constant but the engine speed decreases.
Note: The pressure of the load sensing signal is the highest signal that is commanded by any of the control valves. The signal pressure is not the sum of the signals that are commanded by all of the control valves.
Load sensing signal (3) does not need to increase in order to upstroke the implement pump. If pump supply pressure falls due to increased demand, the pump will upstroke even though load sensing signal (3) has not changed.
For example, if one implement is activated at an operating pressure of 13800 kPa (2000 psi), the load sensing signal pressure is 13800 kPa (2000 psi).
If a second implement is activated at an initial operating pressure of 6900 kPa (1000 psi), the load sensing signal will still be 13800 kPa (2000 psi). The pressure of the supply oil will decrease momentarily as more flow is now demanded by the additional circuit.
The pressure of load sensing signal (3) plus the force of margin spring (4) is now higher than the output pressure of the pump at the bottom end of the spool. Flow compensator spool (2) is pushed to the bottom. Oil from large actuator (8) is vented to the case drain. The angle of swashplate (9) increases and the hydraulic pump provides more flow.
Destroke
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| Illustration 5 | g01305924 |
Implement Pump and Compensator (Destroke) (1) Pressure Compensator Spool (2) Flow Compensator Spool (3) Load Sensing Signal (4) Margin Spring (5) Cutoff Spring (6) Case Drain Passage (7) Pump Output (8) Large Actuator (9) Swashplate (10) Drive Shaft (11) Small Actuator and Bias Spring (12) Piston and Barrel Assembly (13) Signal Passage to Large Actuator (17) Increased Pressure (BB) Cutaway Section (CC) Component Surface (FF) Activated Component (GG) Tank Pressure (JJ) High Pressure (QQ) Reduced Signal Pressure | |
When less flow is required, the pressure of pump output (7) increases due to the greater restriction in the system. Pump output pressure becomes greater than the force of margin spring (4) and reduced load sensing signal (3). Flow compensator spool (2) shifts upward.
When the spool shifts upward, oil flows to large actuator (8). Large actuator (8) overcomes the force of the small actuator and bias spring (11). The angle of swashplate (9) is reduced.
The pump now produces less flow. This condition is known as "destroking".
The pump may destroke under the following conditions:
- An implement is moved to the HOLD position.
- System leakage is reduced.
- A main control spool for a hydraulic control valve is moved to a position that decreases system demand.
- The demand for the implements remains constant, but the engine speed increases.
Note: The pressure of the load sensing signal is the highest signal that is commanded by any of the control valves. The signal pressure is not the sum of the signals that are commanded by all of the control valves.
Load sensing signal (3) does not need to decrease in order to destroke the implement pump. If pump supply pressure increases due to decreased demand, the pump will destroke even though load sensing signal (3) has not changed.
For example, if two implements are activated at operating pressures of 13800 kPa (2000 psi) and 6900 kPa (1000 psi), the load sensing signal pressure is 13800 kPa (2000 psi).
If the implement which is activated at 6900 kPa (1000 psi) is returned to the HOLD position, the pressure of load sensing signal (3) will still be 13800 kPa (2000 psi). However, the pressure of pump output (7) is momentarily increased due to the reduced oil flow that is required in the implement hydraulic circuits.
The output pressure of the pump is now greater than the pressure of load sensing signal (3) and margin spring (4). Flow compensator spool (2) shifts to the top. Oil flows to large actuator (8). The angle of swashplate (9) decreases and the hydraulic pump provides less flow.
Constant Flow
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| Illustration 6 | g01305927 |
Implement Pump and Compensator (Constant Flow) (1) Pressure Compensator Spool (2) Flow Compensator Spool (3) Load Sensing Signal (4) Margin Spring (5) Cutoff Spring (6) Case Drain Passage (7) Pump Output (8) Large Actuator (9) Swashplate (10) Drive Shaft (11) Small Actuator and Bias Spring (12) Piston and Barrel Assembly (13) Signal Passage to Large Actuator (18) Reduced Pressure (BB) Cutaway Section (CC) Component Surface (FF) Activated Component (GG) Tank Pressure (JJ) High Pressure (KK) First Pressure Reduction (PP) Signal Pressure | |
The production of constant oil flow by the implement pump is a combination of upstroking and destroking. Due to fluctuations in the system during operation, the pump upstrokes or the pump destrokes until the system stabilizes.
When constant flow of oil is demanded by an implement hydraulic circuit, load sensing signal (3) acts on the top end of flow compensator spool (2). The pressure of pump output (7) acts on the bottom of flow compensator spool (2) .
Flow compensator spool (2) constantly meters oil to large actuator (8) in order to equalize the pressures on the top and the bottom of the spool. The system stabilizes and swashplate (9) is held at a relative constant angle in order to maintain the required flow.
High Pressure Stall
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| Illustration 7 | g01305974 |
Implement Pump and Compensator (High Pressure Stall) (1) Pressure Compensator Spool (2) Flow Compensator Spool (3) Load Sensing Signal (4) Margin Spring (5) Cutoff Spring (6) Case Drain Passage (7) Pump Output (8) Large Actuator (9) Swashplate (10) Drive Shaft (11) Small Actuator and Bias Spring (12) Piston and Barrel Assembly (13) Signal Passage to Large Actuator (17) Increased Pressure (BB) Cutaway Section (CC) Component Surface (FF) Activated Component (GG) Tank Pressure (JJ) High Pressure (PP) Signal Pressure | |
Pressure compensator spool (1) is in parallel with flow compensator spool (2). Pressure compensator spool (1) limits the maximum system pressure at any pump displacement.
Pressure compensator spool (1) is forced downward during normal operation by cutoff spring (5). If pump output pressure is enough to overcome the force of cutoff spring (5), pressure compensator spool (1) shifts upward.
When the spool shifts, pump oil is allowed to flow to large actuator (8). The increase in pressure in large actuator (8) overcomes the force of the small actuator and bias spring (11). The angle of swashplate (9) decreases and the hydraulic pump destrokes.
Note: When the pump is in the HIGH PRESSURE STALL condition, the activation of a second implement will cause the pressure of pump output (7) to drop. When pump output pressure drops, pressure compensator spool (1) shifts downward. Large actuator (8) is opened to the drain. The pump upstrokes until the pressure of pump output (7) increases to the HIGH PRESSURE STALL condition.