BENDIX R-8 RELAY VALVE

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

BENDIX R-8 RELAY VALVE Specifications

General

Brand	BENDIX
Model	R-8 RELAY VALVE
Category	Control Unit
Language	English

Summary

Bendix R-8 Relay Valve Description and Operation

Description

Explains the function and features of the R-8™ relay valve in air brake systems.

General Operation

Describes how the valve reacts to control pressures for brake application and release.

Applying

Details the process of applying air pressure to the valve for brake engagement.

R-8 Valve Operational States and Features

Balanced State

Describes the piston's movement when delivery air pressure balances service air pressure.

Releasing

Explains the process of exhausting air pressure from the service port.

Anti-Compounding Feature

Details the feature for simultaneous service and park brake application.

R-8 Valve Maintenance and Service Procedures

Preventive Maintenance

Outlines general maintenance intervals and advice for valve inspection.

Operating and Leakage Test

Provides procedures for testing valve operation and identifying leaks.

Removing the Valve

Details the steps for safely removing the R-8™ valve from a vehicle.

Disassembly

Explains how to take the R-8™ valve apart for inspection or repair.

R-8 Valve Assembly and Installation

Cleaning and Inspection

Guides on cleaning metal parts and inspecting for wear or damage.

Assembly

Provides steps and torque specifications for reassembling the valve.

Installation

Details on mounting the valve and connecting air lines.

Safety Precautions

Critical warnings and general precautions for working on the vehicle.