Emergency / Parking Brake Control Valve (Pp-1); Optional Emergency / Parking Brake Overrule Control Valve (Rd-3); Flip-Flop Control Valve (Tw-1) - PREVOST H3-41 Maintenance Manual

SECTION 12: BRAKE AND AIR SYSTEM
13.1

EMERGENCY / PARKING BRAKE CONTROL VALVE (PP-1)

A push-pull control valve mounted on the L.H. lateral console is provided for
parking brake application or release. The spring brakes are self-actuated
whenever the control valve supply pressure drops below 60 psi (414 kPa).
In the UP position, brakes are ON. In the DOWN position, brakes are
RELEASED. A protective case around the knob prevents accidentally
releasing the brakes.
Maintenance and repair information on this valve is supplied in the
applicable booklet, found on your Technical Publications USB flash drive,
under reference number Bendix SD-03-3611.
13.2 OPTIONAL EMERGENCY / PARKING BRAKE OVERRULE
CONTROL VALVE (RD-3)
A RD-3 control valve is used when the vehicle is equipped with the optional
parking brake overrule system. In the case of self-application of spring
brakes due to a pressure drop, the brakes can be released by holding down
this control valve.
Maintenance and repair information on this valve is supplied in the
applicable booklet, found on your Technical Publications USB flash drive,
under reference number Bendix SD-03-3611.
13.3

FLIP-FLOP CONTROL VALVE (TW-1)

A flip-flop control valve mounted on the L.H. lateral console is provided to
unload and lift tag axle air springs. Another one controls the low-buoy
system (coaches only). It is a manually operated "on-off" valve.
Maintenance and repair information on this valve is supplied in the
applicable booklet, found on your Technical Publications USB flash drive,
under reference number Bendix SD-03-3602.
20 PA1621 Maintenance Manual All Series | Revised June 2020