 | |
| Illustration 1 | g00303023 |
(1) Parking and secondary brake control valve | |
 | |
| Illustration 2 | g00303024 |
Parking and secondary brake control valve (2) Knob (3) Valve body (4) Spring (5) Orifice (6) Outlet port to brake actuators (7) Inlet port from air reservoir (8) Exhaust port to atmosphere (9) Valve assembly | |
When the reservoir is discharged, the secondary brake control valve will be in the ON position. The secondary brake control valve is in the ON position when knob (2) is pulled out. Valve (9) will be seated against the upper face of valve body (3) . This will isolate pressurized air from outlet port (6) and exhaust port (8) . Air pressure in the reservoir is allowed to increase to the operating range.
When the air pressure gauge registers a pressure within the operating range, the operator must push knob (2) and the operator must hold knob (2) in order to release the brakes. Pressurized air from the reservoir enters the valve through inlet port (7) . The air then passes through orifice (5) . The air then exits through outlet port (6) to the brake actuators, which release the brakes. Air pressure then holds valve (9) seated over exhaust port (8) .
The secondary brake control valve can be actuated manually or the secondary brake control valve can be actuated by a pressure reduction in the air system. To actuate the valve manually, the operator must pull knob (2) .
If the air system fails or if the pressure drops below approximately 280 kPa (40 psi), spring (4) will unseat valve (9) . This will cause the pressurized air to exhaust to the atmosphere, which will apply the brakes.