HYDRAULIC AR 2159078 - Caterpillar

Air Pressure Reducing Valve
Air Pressure Reducing Valve
1. Control Spring 2. Piston 3. Return Spring 4. Inlet Valve 5. Exhaust Seat 6. Inlet Port 7. Delivery Port 8. Inlet Seat 9. Valve Guide 10. VentThe air supply from the air dryer is reduced to approximately 450 kPa (65 p.s.i.) by the pressure reducing valve.The control spring (1) holds down the piston (2). The return spring (3) holds the inlet valve (4) against the piston at exhaust seat (5). The air supply enters the valve at inlet port (6), flows past the inlet valve and out through the delivery port (7).When the applied pressure which is felt under the piston (2) overcomes the force of the control spring (1), the piston rises. This allows the return spring (3) to raise the inlet valve onto its seat (8), cutting off the air supply.When the pressure in the delivery line drops, the control spring overcomes the reduced air pressure and moves the piston down. The piston pushes the inlet valve off its seat allowing more air to flow to the delivery line until the set pressure is reached again.If the pressure of the air in the delivery line exeeds the set value, the air pressure under the piston will overcome the force of the control spring and the piston will rise, uncovering exhaust seat (5). Excess air pressure in the delivery line will flow past the exhaust seat (5), through the hollow piston and exhaust to atmosphere at vent (10). This will continue until the delivery pressure drops sufficiently to be overcome by the control spring. The piston will then move down into contact with the inlet valve, closing the exhaust seat and maintaining the correct pressure in the delivery line.The air pressure reducing valve is located in the air system module.
Location of Air Pressure Reducing ValveRetarder Solenoid Valve
Retarder Solenoid Valve
1. Solenoid 2. Exhaust Passage 3. Spool 4. Passage to Retarder Control Valve 5. Inlet Passage from Retarder Hand Control Valve 6. Return SpringThe retarder solenoid valve disengages the retarder when the transmission input shaft speed falls below 800 rpm. by cutting off the air supply to the retarder control valve.When the torque converter is locked up the solenoid (1) is energized. The torque converter is locked up when the transmission input shaft speed is above 1380 rpm with the retarder control disengaged, or above 900 rpm with the retarder control engaged. Once the retarder is engaged the torque converter remains locked up until the transmission input shaft speed falls to 800 rpm.When the solenoid (1) is energized, spool (3) moves down and passage (5) is connected to passage (4). Passage (4) is connected to the retarder control valve. The retarder control valve spool is offset by air pressure from passage (5). The retarder control valve then directs torque converter outlet oil to the retarder cavity.When the transmission input shaft speed falls to 800 rpm, the speed switch de-energizes the solenoid (1). The spool (3) is moved up by return spring (6)