UNION AS 3295473 - Caterpillar

Brake Control Valve
Two brake control valves are used in the braking system. The operation is the same for each valve.When the brake control valve treadle is depressed, a force is exerted on seat (1). The force compresses rubber spring (2) and moves piston assembly (3) downward. The exhaust valve seat (7) contacts and closes exhaust port (12) in valve (9). Continued downward movement of the piston assembly pushes the valve (9) off inlet valve seat (8). Pressure air from inlet port (13) passes around the valve and out through outlet port (5). Air travels to the double check valve, air chamber and transmission neutralizer control valve when the left brake treadle is depressed, or to the double check valve and air chamber when the right brake treadle is depressed.
BRAKE CONTROL VALVE
1. Seat. 2. Rubber spring. 3. Piston assembly. 4. Retainer. 5. Outlet port. 6. Spring. 7. Exhaust valve seat. 8. Inlet valve seat. 9. Valve. 10. Valve body. 11. Valve spring. 12. Exhaust port. 13. Inlet port. 14. Exhaust diaphragm.When the air pressure below piston assembly (3) becomes greater than the force exerted above the piston, the piston lifts sufficiently to permit valve (9) to move upward and seat. This blocks off further supply of pressure air. Piston assembly (3) remains seated against valve (9), preventing any loss of air pressure through exhaust port (12). Thus, the brake control valve is in a balanced position and air pressure is held in the lines and air chambers.If the treadle is partially raised, mechanical force above piston assembly (3) is decreased. The greater force below the piston assembly, exerted by pressure air and spring (6), lifts the piston assembly, unseating it from valve (9). Pressure air in the lines and air chambers is permitted to escape past exhaust diaphragm (14) until forces above and below the piston are balanced. When the treadle is completely raised, piston assembly (3) will remain unseated from valve (9), exhausting all pressure air to atmosphere and releasing the brakes. Valve (9) is held in its seat by valve spring (11).Emergency And Parking Brake Control Valve
With the air reservoir discharged, the emergency and parking brake control valve will be in the released position. [knob (1) pulled out.] Valve (8) will be seated against upper face of valve body (2) sealing off pressure air supply to outlet port (5), and exhaust port (7). Air pressure in the reservoir is allowed to build to the operating range.When the air pressure gauge registers in the operating range, the operator must push in and hold knob (1) on the emergency and parking brake control valve to release the parking brakes. Pressure air from the reservoir enters the valve through inlet port (6), passes through orifice (4), and outlet port (5) to the protective brake chambers, releasing the parking brakes. Air pressure then holds valve (8) seated over exhaust port (7).
FLOW OF AIR (BRAKES APPLIED)
1. Knob and pin assembly. 2. Valve body. 3. Spring. 4. Orifice. 5. Outlet port (to protective