Cylinders Tilt Cylinder Ride Control Accumulator Auxiliary Function Tank Hydraulic Lockout Valve Steering Pilot Supply (CCS Only) Margin Relief Valve Pilot Accumulator Pilot Pressure Reducing Valve Signal Duplication Valve Signal Relief Valve Manual Lower Valve Tilt Antidrift Valve Case Drain Filter Balance Valve Ride Control Relief Valve Lift Ant idrift
Valve Choke Check Valve Dump Pilot Solenoid Valve Lower / Float Pilot Solenoid Valve Raise Pilot Solenoid Valve
Tilt Back Pilot Solenoid Valve Line Relief Valves Screen Tilt Spool Lift Spool Pressure Compensator Valve Resolver Valve Resolver Valve Resolver Valve Pressure Compensat or Valve
Auxiliary Rod End Solenoid Valve Auxiliary Head End Solenoid Valve Cover Manifold Inlet Manifold Pressure Compensator Valve Auxiliary Spool Ride Control Head End Solenoid valve Rod End Solenoid Valve Pump and Pump Cont rol Valve Min Angle Check Valve Resolver Valve
When the engine is started and the implement control levers are in the HOLD position, the implement pump supplies standby oil flow to the 3PC valve group.
The oil flows into the inlet manifold and is divided into two paths. The supply path for the implements flows through the inlet manifold into the tilt section where the flow path is divided again. One path flows to the tilt spool and is blocked. The second path flows to the lift control section, to the ride control section, to the optional auxiliary section, and to the cover manifold. Within the cover manifold, the oil flows to both the pilot pressure reducing valve (PRV) and the differential pressure relief valve. The differential pressure relief valve maintains a difference between the load sensing pressure and the pump supply oil pressure of 3000 kPa (435 psi). When all of the control valves are in the HOLD position, the implement pump is at low pressure standby. The differential pressure relief valve maintains the minimum pressure for low pressure standby. The standby pressure is directed to the pilot pressure reducing valve (PRV). The pilot pressure reducing valve provides a regulated pilot oil pressure to activate the control valves as needed.
The pilot oil flows from the PRV through the check valve to the pilot accumulator and the hydraulic lockout solenoid valve. If the wheel loader is equipped with the optional Command Control Steering (CCS), the oil flow will be shared by the implement pilot system and the steering pilot system.
The hydraulic lockout solenoid valve is in the CLOSED position until the hydraulic lockout switch in the cab is activated. When the solenoid valve is energized, the solenoid valve opens and pilot oil flows to the various implement function solenoid valves.
The second path of oil in the inlet manifold flows through the screen to the signal duplication valve. The signal duplication valve uses highest work port pressure in the resolver network to supply an identical pressure to the pump control valve.
When all implement control valves are in the HOLD position, there is no load sensing signal in the resolver network. With no load sensing pressure present, the implement pump supplies low pressure standby.
88
Tilt Control Valve - HOLD
With the tilt control valve in the HOLD position, the springs on each end of the control spool keep the spool centered. The control spool blocks the flow of pump supply oil to the pressure compensator valve.
The bridge passage is open to tank through the internal passage in the control spool and there is no oil flow to the resolver valve. With no oil flow to the resolver network, there is no signal to the signal duplication valve and the signal pressure to the pump control valve is matching the oil pressure in the resolver network. The implement pump is at low pressure standby.
From Signal Duplication Valve
To / From Rod End of Cylinder Pressure Compensat or Valve Line Relief and Makeup Valve Bridge Passage Tilt Antidrift Valve Feeder Passage Internal Passage Control Spool Line Relief and Makeup Valve Supply Passage
To Signal Duplication Valve From Resolver Valves
Rackback Pilot Solenoid Valve
Dump Pilot Solenoid Valve To / From Head End
of Cylinder
89
Implement Hydraulic System - DUMP
When the tilt lever is moved to the DUMP position, the Implement ECM energizes the dump proportional solenoid and the tilt antidrift valve. As the control valve initially shifts to the left, and there is pressure in the rod end of the tilt cylinder, the pressure goes around the control spool to the bridge passage. The pressure in the bridge passage goes to the resolver network and to the signal duplication valve to upstroke the implement pump. The pressure also goes to the spring chamber in the center of the pressure compensator valve. The lower half of the pressure compensator valve shifts down to block the oil flow from the bridge passage to the feeder passage.
As the tilt control spool continues shifting to the left, pump supply oil flows around the center land on the control spool to the feeder passage. Oil pressure in the feeder passage lifts the pressure compensator valve up. Pump supply oil goes through the orifices in the lower end of the compensator valve to the bridge passage. From the bridge passage, the pump flow goes around the control spool into the work port to the rod end of the tilt cylinder.
Returning oil from the head end of the tilt cylinder, flows around the tilt antidrift valve to the tank port.
From Signal Duplication Valve
To Rod End of Cylinder Pressure Compensat or Valve Line Relief and Makeup Valve Bridge Passage Tilt Antidrift Valve Feeder Passage Internal Passage Control Spool Line Relief and Makeup Valve Supply Passage
To Signal Duplication Valve From Resolver Network
Tilt Back Pilot Solenoid Valve
Dump Pilot Solenoid Valve From Head End
of Cylinder
"H" SERIES MEDIUM WHEEL LOADER TILT CONTROL VALVE
90
Pressure Compensator Valve - HOLD
When the control spool is in the HOLD position, the load check spool and the pressure compensator valve are held down by the spring force on top of the load sense spool. Pump supply oil in the supply passage is blocked by the control spool. No supply oil from the supply passage flows to the feeder passage. Therefore, no load sensing pressure is directed to the implement pump control valve. The implement pump is at low pressure standby.
From Signal Duplication Valve
To Rod End
of Cylinder Load Check Spool
Line Relief and Makeup Valve Bridge Passage Tilt Antidrift Valve Feeder Passage Internal Passage Control Spool Line Relief and Makeup Valve Supply Passage
To Signal Duplication Valve From Resolver Network
Tilt Back Pilot Solenoid Valve
Dump Pilot Solenoid Valve From Head End
of Cylinder
HOLD
Pressure Compensator
91
Load Check Operation
This illustration shows the pressure compensator and load check valve in the load check operation. When the control spool is initially shifted to the left, work port pressure from the rod end of the cylinder (if any) flows around the right end of the control spool into the bridge passage. The pressure goes through the holes between the pressure compensator valve and the load check spool. The pressure moves the pressure compensator spool down and the load check spool up. With the pressure compensator valve shifted down, no pressure can go from the bridge passage to the feeder passage. The pressure compensator valve serves as a load check valve to hold the load up to prevent it from dropping.
The pressure in the bridge passage is directed through the resolver network to the signal duplication valve. The signal duplication valve generates a load sensing signal pressure equal to the work port pressure. The load sensing signal pressure is directed to the top of the spring chamber on top of the load sense spool. The load sensing signal pressure is also directed to the pump control valve to upstroke the pump (not shown).
From Signal Duplication Valve
To Rod End of Cylinder Load Check Spool Line Relief and Makeup Valve Bridge Passage Tilt Antidrift Valve Feeder Passage Internal Passage Control Spool Line Relief and Makeup Valve Supply Passage
To Signal Duplication Valve From Resolver Network
Tilt Back Pilot Solenoid Valve
Dump Pilot Solenoid Valve From Head End
of Cylinder