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| Illustration 1 | g00303963 |
(1) Retarder air control valve | |
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| Illustration 2 | g00304938 |
Retarder air control valve (2) Head (3) Handle (4) Cam follower (5) Cam (6) Pressure regulating spring (7) Exhaust valve seat (8) Exhaust valve (9) Spring (10) Piston (11) Piston return spring (12) Inlet valve seat (13) Delivery port (14) Inlet valve (15) Supply port (16) Exhaust port | |
The retarder air control valve controls the braking capacity of the retarder by metering air pressure to the retarder air circuit. As handle (3) is pulled closer to the operator, the braking capacity of the retarder is increased.
As handle (3) is moved toward the operator, head (2) and cam follower (4) are rotated. This exerts a force on pressure regulating spring (6) through cam follower (4) and cam (5) .
The force on the pressure regulating spring moves piston (10) downward. This engages exhaust valve seat (7) with exhaust valve (8) , which seals exhaust port (16) from delivery port (13) . Exhaust valve (8) and inlet valve (14) are a rigid assembly. Therefore, after exhaust valve (8) is closed and piston (10) continues downward, inlet valve (14) is forced from seat (12) . This permits air pressure from supply port (15) to flow past inlet valve (14) to delivery port (13) in order to actuate the retarder valve.
When the air pressure below piston (10) overcomes the mechanical force above piston (10) , piston (10) rises enough to permit inlet valve (14) to move upward in order to seat. When inlet valve (14) seats, further supply of air pressure is cut off. Exhaust valve (8) remains seated. This prevents any loss of air pressure through exhaust port (16) . Thus, the retarder air control valve is in a balanced position because the forces on either side of the piston are equal.
If handle (3) is partially moved toward the OFF position, the mechanical force above piston (10) is decreased. A greater force below the piston is caused by air pressure and piston return spring (11) . This force lifts piston (10) , which unseats exhaust valve (8) until a decreased pressure is established in order to balance the decreased mechanical force above piston (10) . When handle (3) is moved to the OFF position, exhaust valve (8) will remain open. This will exhaust all air pressure from the retarder control group. Inlet valve (14) is held seated by spring (9) .
Note: On the 627F Wheel Tractor-Scraper, the retarder air control valve controls both the tractor and scraper retarder control groups. A tee is in the line from the retarder air control valve to the scraper retarder. When the retarder is operated, air pressure is sent through the tee to the lockup clutch valve for the scraper torque converter. The torque converter is then engaged in direct drive. The torque converter can then give assistance to the retarder in order to slow the machine.