Self lapping SA-9 independent air brake is providing for application and release of air Brakes on loco. Independent valve handle movement towards application position feeds pre-regulated by the regulating portion of the SA-9 independent brake valve passes through MU-2V valve, F-I selector valve and double check valve to actuate C-2 w relay valve which in turn connects the main reservoir air to brake cylinder to apply brakes. The brake control stand. Minor leakage within limts in the brake cylinder is automatically compensated by the C2W relay valve.
Then the handle of the independent brake valve is brought back towards released position. The air pressure is reduced through the exhaust port of independent brake valve. This actuate C2W relay valve to exhaust the air form brake cylinders to atmosphere, for releasing brakes.
The port No’s 1 and 7 of SA-9 independent brake valves are plugged and locomotive brake release switches are provided on both the driver control stand whenever driver wants to release the loco brakes during or after automatic brake application, driver has to press the loco and brake release switch. The D-1 pilot air valve is energized to cut-off air brakes on loco and brake cylinder will be connected to atmosphere while train brakes remain applied on trailing stock.