Bendix Commercial Vehicle Systems R-8P PRESSURE EQUALIZING PILOTRELAY - Manual

1
®
SD-03-1061A
Bendix ® R-8P ™ Pressure Equalizing Pilot Relay Valve
DELIVERY
PORTS
SUPPLY PORT
SPRING
FIGURE 1 - CUTAWAY AND EXTERNAL VIEW
VENT
PISTON
BODY
SERVICE
(CONTROL)
PORT
EXHAUST INLET/EXHAUST
VALVE ASSEMBLY
DESCRIPTION
The R-8P ™ pressure equalizing pilot relay valve is a device
designed to reinforce the control signal on long wheel base
towing trailers and converter dollies.
Unlike a standard relay valve which typically has a 4 p.s.i.
crack pressure and similar differential between control and
delivery, the R-8P
™ valve has a 0 p.s.i. differential.
On the converter dolly and long wheel base towing trailers,
the R-8P
™ valve reinforces the service brake application
signal without the differential found in standard relay valves.
The 0 p.s.i. differential of the R-8P
™ valve assures that all
trailer and dolly brakes will receive the same strength control
signal even during light brake applications.
By providing a balanced pressure signal to all trailer and
dolly brakes, the R-8P
™ valve helps achieve overall vehicle
brake balance and stability. The R-8P ™ valve also helps
improve brake lining wear balance on combination vehicles
by causing even the most distant brake to contribute its
share of braking effort.
OPERATION
APPLICATIONS (FIG. 2)
When a service brake application is made, air delivered from
the brake valve enters the service port of the R-8P
™ valve.
As air pressure fills the space above the piston, it begins to
force the piston down. Because of the spring force above
the piston, the piston exhaust seat is already in contact
with the inlet/exhaust valve, sealing off the exhaust. As the
piston begins to move downward it forces the inlet/exhaust
valve off the inlet seat, allowing air from the reservoir to be
delivered out the delivery ports of the R-8P
™ valve in direct
proportion to the pressure received at the service port.
Any differential between service and delivery pressure caused
by friction or resistance to the movement of the piston
(commonly called crack pressure and normally in the range
of 2 to 4 p.s.i.) is eliminated due to passage of air through
the orifice in the piston.
COVER
SUPPLY PORT
DELIVERY PORT
PISTON
ORIFICE