1
SD-03-1063
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
™
valve.
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.
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,
the R-12P
™
valve aids in achieving overall vehicle brake
pressure balance, timing balance, and stability.
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
™
valve in a trailer air brake
schematic. Note that additional air lines for a towing trailer
are shown as dashed lines.
The R-12P
™
valve uses the R-12
™
valve family lower body
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:
Qty. Size
Supply (SUP) 2 1/2”
Delivery (DEL) 4 3/8”
Control (CON) 1 1/4”
Exhaust (EXH) 1 --
Bendix
®
R-12P
™
Pilot Relay Valve
3/8”
DELIVERY
1/2” SUPPLY (2)
RESERVE
SPRING
1/4” CONTROL
LOAD
PISTON
BODY
EQUALIZING
ORIFICE
EXHAUST
INLET/EXHAUST
VALVE
COVER
1/2”
SUPPLY
3/8” DELIVERY (4)
RELAY
PISTON
1/4” CONTROL
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