Auxiliary Hydraulic System Schematic (Hold)
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| Illustration 1 | g01189554 |
When the auxiliary hydraulic pump is at rest, the swashplate spring forces the swashplate to the maximum angle. When the engine is started, the auxiliary hydraulic pump generates flow.
Pump supply oil acts on the pressure compensator spool. Supply oil acts against the force of the spring. System pressure causes the pressure compensator spool to shift. This shift directs oil into the displacement piston cavity.
Pressure in the displacement piston cavity works against the bias spring. As the pressure in the displacement cavity increases, the displacement piston moves the swashplate toward the minimum angle. As the swashplate angle decreases, the displacement piston uncovers a passage. This passage allows oil to flow from the displacement piston cavity into the pump case.
At this point, supply pressure decreases. The force from the pressure compensator spring causes the pressure compensator spool to shift. This shift opens the displacement piston cavity to the pump case drain. In this case, the bias spring causes the swashplate angle to increase.
As the angle of the swashplate increases, the pressure in the system increases. The pressure compensator spool senses the increase in pressure. The pressure compensator spool shifts, and supply oil is directed into the displacement piston cavity. Eventually, the pressure compensator spool and the bias spring reach equilibrium. In this state the auxiliary hydraulic pump generates just enough flow to maintain the pressure in the system at 13780 ± 172 kPa (2000 ± 25 psi).
Output from the auxiliary pump is sent to the following places:
- The pressure manifold
- The screed extension manifold
- The auxiliary control manifold
The pressure manifold distributes oil to the following places:
- Left tow point valve
- Right tow point valve
- Truck hitch manifold
- Track take up system
All valves in the auxiliary hydraulic system are closed centered.
The auxiliary hydraulic system is used to charge the hydraulic side of the track tension accumulators. The track tension accumulators are charged to 13780 ± 172 kPa (2000 ± 25 psi) with a 12402 kPa (1800 psi) nitrogen precharge.
Each track tension manifold contains a shutoff valve which locks the pressure in the track tension system. The pressure in the accumulator is transferred to the track tension cylinder. This pressure provides the force which maintains the belt tension.
The auxiliary manifold is equipped with a flow control valve. This valve is located in the passage that goes to the fumes motor. The flow control valve maintains the flow to the fumes motor at a constant rate. The line to the fumes motor contains a shutoff valve. When this valve is closed, the fumes motor does not operate.
Auxiliary Hydraulic System Schematic (Operating)
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| Illustration 2 | g01189580 |
This schematic shows the auxiliary hydraulic system in the following conditions:
- Tow pints (INCREASE)
- Truck hitch (OPEN)
- Screed extensions (EXTEND)
- Screed (LIFT)
- Auger (LIFT)
- Hopper (LIFT)
- Speed range (TRAVEL)
- Parking brake (RELEASED)
- Track tension shutoff valve (CLOSED)
Note: During normal operation, these conditions would not simultaneously occur. The circuit is shown under these conditions for illustration purposes only.
When an active left tow point switch is in the UP position, the left tow point raise solenoid is energized. The left tow point control valve directs oil to the counterbalance valve. The counterbalance valve consists of two check valves and two spools.
Oil flows through the check valve of the counterbalance valve and into the head end of the left tow point cylinder. The cylinder begins to extend. This extension displaces oil from the rod end of the cylinder. Displaced oil from the rod end of the cylinder flows to the return side of the counterbalance valve. Initially, the counterbalance valve blocks the return oil. As the pressure in the line to the head end of the tow point cylinder increases, the spool in the line to the rod end of the cylinder shifts. This shift opens a passage which allows return oil from the rod end of the cylinder to flow into the return filter in the hydraulic tank.
Note: The right tow point system follows the same principles of operation as the left.
At the truck hitch manifold, pump supply oil flows through a pressure reducing valve. This valve limits the downstream pressure to 6900 kPa (1000 psi). When the active truck hitch switch is in the OPEN position, the truck hitch open solenoid is energized. The truck hitch control valve opens a passage which allows the reduced supply oil to act against the pilot opened check valve. The check valve opens, and supply oil flows to the head ends of the truck hitch cylinders.
Return oil from the rod ends of the cylinders flows in the following places:
- Through the pilot opened check valve
- Across the truck hitch control valve
- To the return filter in the hydraulic tank
When an active left screed extension switch is in the EXTEND position, the left screed extend solenoid is energized. The screed extend control valve opens a passage which allows the pump supply oil to act against the pilot opened check valve. The check valve opens, and supply oil flows to the head end of the left screed extend cylinder.
Return oil from the rod end of the cylinder flows through the following components:
- The pilot opened check valve
- Across the screed extend control valve
- To the return line in the auxiliary manifold
Note: The right screed extension system follows the same principles of operation as the left.
When the active screed lift switch is in the LIFT position, the screed lift solenoid is energized.
Pump supply oil flows in the following places:
- Across the screed lift valve
- Through the screed lower valve
- Into the rod ends of the screed hoist cylinders
As the screed hoist cylinders retract, displaced oil from the head ends of the cylinders is sent into the return line in the auxiliary manifold.
When the active auger lift switch is in the LIFT position, the auger lift solenoid is energized. Pump supply oil flows across the auger lift valve to the pilot opened check valves. Supply oil flows through the pilot opened check valve which is in the line to the rod end of the right auger hoist cylinder. Supply oil opens the pilot opened check valve which is in the line to the head end of the left auger hoist cylinder.
As supply oil flows into the rod end of the right auger hoist cylinder, the cylinder retracts. Cylinder movement displaces oil from the head end of the right auger hoist cylinder. The displaced oil is directed into the rod end of the left auger hoist cylinder. This action causes the left cylinder to retract.
Displaced oil from the head end of the left auger hoist cylinder flows in the following places:
- Through the pilot opened check valve
- Across the auger lower valve
- Into the auxiliary manifold return line
When the active hopper control switch is in the LIFT position, the hopper raise solenoid is energized. Pump supply oil flows across the hopper raise valve to the pilot opened check valves. Supply oil flows through the pilot opened check valve which is in the line to the rod end of the hopper hoist cylinders. Supply oil opens the pilot-opened check valve which is in the line to the head end of the cylinders. After the supply oil leaves the auxiliary manifold, the flow is split into two streams: one stream leads to the rod end of the left hopper hoist cylinder; the other stream leads to the rod end of the right hopper hoist cylinder. Both flow paths contain an orifice.
As the hopper hoist cylinders retract, displaced oil from the head ends of the cylinders flows back to the auxiliary manifold.
Inside the manifold, return oil flows through the following components:
- The pilotopened check valve
- Across the hopper lower valve
- Into the auxiliary manifold return line
When the active propulsion mode switch is in the TRAVEL position, the shift solenoid is energized (refer to Propulsion Control System for details about this electrical circuit). The pressure reducing valve which is upstream from the shift valve in the auxiliary manifold reduces the downstream pressure to 4140 ± 345 kPa (60 ± 50 psi). The reduced pressure oil flows across the shift valve and into the right shift cylinder and into the left shift cylinder. This causes the machine to operate in the travel speed range.
When the active parking brake switch is in the OFF position and all other brake release parameters are met (refer to Propulsion Control System for details about this electrical circuit), the parking brake solenoid is energized. Under these conditions, pump supply oil flows across the parking brake valve to the brake release manifold. When the needle valve which is inside the brake release manifold is open, supply oil flows out of the brake release manifold to the right brake cylinder and to the left brake cylinder.
Note: When the needle valve which is in the brake release manifold is closed, the hand pump can be used in order to manually release the parking brakes.
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| Illustration 3 | g01191668 |
This schematic shows the auxiliary hydraulic system in the following conditions:
- Tow points (DECREASE)
- Truck hitch (CLOSE)
- Screed extensions (RETRACT)
- Screed (FLOAT)
- Auger (LOWER)
- hopper (LOWER)
- speed range (TRAVEL)
- parking brake (RELEASED)
Note: During normal operation, these conditions would not simultaneously occur. The circuit is shown under these conditions for illustration purposes only.
When an active left tow point switch is in the DOWN position, the left tow point lower solenoid is energized. The left tow point control valve directs oil to the counterbalance valve. The counterbalance valve consists of two check valves and two spools.
Oil flows through the check valve of the counterbalance valve and flows into the rod end of the left tow point cylinder. The cylinder begins to retract. This retraction displaces oil from the head end of the cylinder. Displaced oil from the head end of the cylinder flows to the return side of the counterbalance valve. Initially, the counterbalance valve blocks the return oil. As the pressure in the line to the rod end of the tow point cylinder increases, the spool in the line to the head end of the cylinder shifts. This shift opens a passage which allows return oil from the head end of the cylinder to flow to the return filter in the hydraulic tank.
Note: The right tow point system follows the same principles of operation as the left.
At the truck hitch manifold, pump supply oil flows through a pressure reducing valve. This valve limits the downstream pressure to 6900 kPa (1000 psi). When the active truck hitch switch is in the CLOSE position, the truck hitch close solenoid is energized. The truck hitch control valve opens a passage which allows the reduced supply oil to act against the pilot-opened check valve. The check valve opens, and supply oil flows to the rod ends of the truck hitch cylinders. Return oil from the head ends of the cylinders flows in the following places: through the pilot-opened check valve; across the truck hitch control valve; to the return filter in the hydraulic tank.
When an active left screed extension switch is in the RETRACT position, the left screed retract solenoid is energized. The screed extend control valve opens a passage which allows the pump supply oil to act against the pilot-opened check valve. The check valve opens, and supply oil flows to the rod end of the left screed extend cylinder. Return oil from the head end of the cylinder flows in the following places: through the pilot-opened check valve; across the screed extend control valve; and to the return line in the auxiliary manifold.
Note: The right screed extension system follows the same principles of operation as the left.
When all the screed lift switches are in the FLOAT position, and the screed counterbalance switch is in the OFF position, the screed lower solenoid is energized. Under these conditions, the rod ends of the screed hoist cylinders are open to the return line in the auxiliary manifold.
Gravity causes the screed to lower, and oil is displaced from the rod ends of the screed hoist cylinders. Orifices in the lines to the rod ends of the cylinders limit the speed at which the screed lowers. As oil is displaced from the rod ends of the screed hoist cylinders, a vacuum is created in the head ends of the cylinders. This vacuum draws oil from the hydraulic tank in order to fill the void in the head ends of the cylinders.
When the active auger lift switch is in the LIFT position, the auger lift solenoid is energized. Pump supply oil flows across the auger LIFT valve to the pilot-opened check valves. Supply oil flows through the pilot-opened check valve in the line to the rod end of the right auger hoist cylinder. Supply oil opens the pilot-opened check valve which is in the line to the head end of the left auger hoist cylinder.
As supply oil flows into the rod end of the right auger hoist cylinder, the cylinder retracts. Cylinder movement displaces oil from the head end of the right auger hoist cylinder. The displaced oil is directed into the rod end of the left auger hoist cylinder. This action causes the right cylinder to retract. Displaced oil from the head end of the left auger hoist cylinder flows in the following places: through the pilot-opened check valve; across the auger lift valve; into the auxiliary manifold return line.
Auxiliary Hydraulic System Schematic (Screed Assist)
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| Illustration 4 | g01189582 |
The pressure reducing valve for the screed counterbalance system reduces the pressure which is available to the screed assist solenoid. When both screed lift switches are in the FLOAT position and the screed counterbalance switch is in the ON position, the screed assist solenoid is energized.
When the screed assist solenoid is energized, reduced pressure oil flows to the rod ends of the screed hoist cylinders. This oil provides a "lift" to the screed. As a result, this reduces the force which the screed exerts on the asphalt mat.
The pressure reducing valve setting can be adjusted. The setting is shown on the gauge which is attached to the port "G2" of the auxiliary control manifold. The higher the pressure setting of the pressure reducing valve, the greater the lift provided to the screed. In general, the minimum screed assist pressure should be approximately 172 kPa (25 psi). The maximum screed assist pressure should be approximately 2670 kPa (400 psi).