Troubleshooting guide

27
For more information, visit www.bendix.com or www.foundationbrakes.com • 1-800-AIR-BRAKE (1-800-247-2725)
The Control System: Push-Pull Valves
Spring
Brakes
S
D
E
E
D
S
Bendix
®
PP-1
®
Valve
Bendix
®
PP-8
™
Control Valve
Push-Pull Control Valves
Push-pull control valves are most often mounted on the
vehicle dash board and are used for a variety of control
applications. The Bendix
®
PP-1
®
and PP-2
™
valves
are pressure-sensitive, normally-closed, on/off control
valves which automatically return to the exhaust (button
out) position when supply pressure is below the required
minimum. They may be manually operated to either
position when pressure is above the required minimum.
Pressure settings and button confi guration and wording
may vary, depending on application.
The Bendix PP-1 control valve is commonly used to
control parking and emergency brakes. This valve was
also used in conjunction with the Bendix
®
TP-2
™
tractor
protection valve in pre-FMVSS 121 single circuit tractor
air systems.
Unlike most other push-pull control valves, the
Bendix
®
PP-8
™
is nonautomatic, and will remain in the
applied (button in) position regardless of delivery or
supply pressure. The PP-8 control valve is commonly
used to control only the tractor brakes in the (FMVSS
121-compliant) dual system.
The Bendix
®
PP-3
™
control valve is primarily used
to control the Bendix
®
TP-3
®
tractor protection valve in
pre-FMVSS 121 tractor systems. It features a tripper
piston which prevents manual override of the emergency
application of trailer brakes.
Trailer Supply Valve (Tractor Protection Control)
The Bendix
®
PP-7
™
push-pull control valve is a
pressure-sensitive, on/off control valve which will
automatically return to the exhaust (button out) position
when supply pressure is below the required minimum.
Bendix
®
PP-1
®
Control Valve
It may be manually operated to either position when
pressure is above the required minimum. Button
confi guration and wording may vary depending on
application. The automatic exhaust pressure is 40
psi.
The PP-7 valve is used to control the tractor protection
system and is generally identifi ed as the trailer air
supply valve. The valve employs an air-operated
interlock in the lower body which will apply the trailer
brakes when the tractor-spring-applied parking
brakes are activated. The interlock ensures that the
tractor parking brake can not be applied without the
trailer parking brakes also being applied. Normally
this action will not affect the position of the PP-7 valve
button. The interlock of tractor and trailer parking is
stipulated as a part of government regulations (e.g.
FMVSS 121).
Bendix
®
PP-7
™
Control Valve
Bendix
®
PP-3
™
Control Valve
Bendix
®
RD-3
™
Valve
Release
Front
Rear
Supply
Example of a Spring Brake
Air Delivery System