4-15. A-1 CHARGING CUTOFF PILOT VALVE (cont)
When the pressure has been reduced to a predetermined value, spring tension will move the actuating
piston and its spool valve to the lowest position.
Air pressure in the sanding reservoir will then exhaust through the automatic sanding timing choke via
port 9 and the actuating piston spool valve. Air pressure likewise exhausts from chamber C at the
outer face of the cutoff piston.
When the 26-C brake valve handle is moved to EMERGENCY position to reset, the A-1 charging cutoff pilot
valve functions as follows:
Main reservoir air is connected to port 12 from the brake valve and flows past the unseated selector
check valve to chamber B beneath the cutoff piston to force the cutoff piston and its spool valve
upward to their normal release position.
Pipe 53 pressure, supplied with air flow from port 12, cannot be dissipated through the cutoff pilot
valve at the brake valve.
The brake valve handle must be moved to RELEASE position before the pipe 53 air pressure can be
drained and the brakes release. A slight inherent delay in releasing the brakes has been introduced
with the use of this arrangement of break-in-two protection.