1
®
Bendix
®
R-8
™
Relay Valve
SD-03-1061
FIGURE 1
- EXTERIOR
FIGURE 2 -
SECTIONAL
DESCRIPTION
The relay valve in an air brake system functions as a relay
station to speed up the application and release of the brakes.
The valve is normally mounted in the proximity to the
chamber it serves. The valve operates as a remote controlled
brake valve that delivers or releases air to the chambers in
response to the control air delivered to it from the control
point.
The R-8
™
relay valve is designed for either frame or reservoir
mounting. Remote mounted valves generally have one or
two 3/4" supply ports. The reservoir mounted configuration
has an additional 3/4" port through the body mounting flange.
Three delivery ports with various size pipe threads are
provided for piping versatility. A single 1/4" service port is
located in the cover which can be rotated to 90° increments.
The R-8
™
valve incorporates a unique, quick release and
anti-compounding feature located above the service port in
the cover. With the anti-compounding feature not in use,
an exhaust cover is installed. When the anti-compounding
feature is used, removal of the exhaust cover exposes a
1/8" pipe thread balance port. All ports on the valve are
identified.
GENERAL OPERATION
The rapid reaction of the R-8
™
valve to changes in control
pressures is in part due to the relatively small volume of air
required between the valve cover and the relay piston. The
area of the relay piston and the presence of the quick release,
anti-compound feature also contribute greatly to the fast
application and release of the emergency and parking brakes.
APPLYING
Air pressure entering the service port moves the flexible
diaphragm, closing off the exhaust passage of the quick
release. Air also flows around the edge of the diaphragm
and into the cavity between the cover and the top of the
relay piston. Air pressure acting on the surface of the piston
forces it down. The exhaust valve seat moves down with the
piston and seats on the inner or exhaust portion of the inlet
and exhaust valve, sealing off the exhaust passage. At the
same time the outer or inlet port of the inlet and exhaust
valve moves off its seat, permitting supply air to flow from
the reservoir past the open inlet valve and out the delivery
port.
1/4 P.T.
SERVICE
1/2 P.T.
DELIVERY
3/4 P.T.
SUPPLY
EXHAUST
COVER
COVER
ASSY.
DIAPHRAGM
RELAY
PISTON
ASSY.
SCREW
EXHAUST COVER
QUICK
RELEASE
DIAPHRAGM
CAP
NUT
SEALING
RING
O-RING
SCREW
WASHER
O-RING
INLET &
EXHAUST
VALVE
SEALING
RING
PISTON
RETURN
SPRING
