BENDIX R-12P PILOT RELAY VALVE Manual
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®
™
Bendix
R-12P
COVER
1/2" SUPPLY (2)
FIGURE 1 - CUTAWAY AND EXTERNAL VIEW
DESCRIPTION
™
The R-12P
pilot relay valve is designed to speed up
control signal application and release on long non-towing
trailers, towing trailers, dollies, and long wheelbase tractors.
It does this without adversely affecting the control signal.
The R-12P
™
valve replaces the current R-8P
Unlike a standard relay valve used as a "booster," which
typically has a 2-4 psi differential between control and
delivery, the R-12P
™
valve has zero differential. It "speeds"
up control line signal application and release in a train
of vehicles, and it delivers the same air pressure that it
receives. This provides a uniform brake signal to all trailer
and dolly brakes, even during light applications.
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The unique R-12P
valve feature is that it uses a supply
air pressure load to quicken the valve's response time. By
balancing the pressure signal to all trailer and dolly brakes,
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the R-12P
valve aids in achieving overall vehicle brake
pressure balance, timing balance, and stability.
Pilot Relay Valve
1/4" CONTROL
3/8" DELIVERY (4)
™
valve.
RELAY
PISTON
BODY
1/2"
SUPPLY
INLET/EXHAUST
VALVE
It also substantially improves brake lining wear balance
on combination vehicles by making even the most distant
brake contribute its share of braking effort.
Figure 2 shows the R-12P
schematic. Note that additional air lines for a towing trailer
are shown as dashed lines.
™
The R-12P
valve uses the R-12
and standard Bendix mounting brackets. It can also be
reservoir-mounted.
The body and cover are die-cast aluminum, and the valve's
weight is approximately 2.3 lbs. Porting is as follows:
Supply (SUP)
Delivery (DEL)
Control (CON)
Exhaust (EXH)
RESERVE
LOAD
SPRING
PISTON
1/4" CONTROL
EXHAUST
™
valve in a trailer air brake
™
valve family lower body
Qty.
2
4
1
1
EQUALIZING
ORIFICE
3/8"
DELIVERY
Size
1/2"
3/8"
1/4"
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1