Troubleshooting guide

25
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The Control System: Quick Release, Ratio and Modulating Valves
Quick Release, Ratio and Modulating
Valves
Quick Release Valves
The function of quick release valves is to speed up the
exhaust of air from the air chambers. They are mounted
close to the chambers they serve.
Typically, these valves are designed to deliver within
one psi of control pressure to the controlled device;
however for special applications, the valve is available
with greater differential pressure designed into the valve
by the inclusion of a spring or spring seat.
Several styles of quick release valves are available and are
functionally the same. The Bendix
®
QR-1
®
and QR-1C
®
quick release valves have die cast metal bodies. The
Bendix
®
QRN
™
quick release valve is a nonmetallic version.
The Bendix
®
QR-L
™
quick release valve is an inline device.
Ratio Valves
Historically, valves such as the Bendix
®
LQ-4
™
ratio
valves (and Bendix
®
LQ-2
™
and LQ-5
™
limiting valves
not shown) were used in the front axle delivery line of
vehicles. During normal service brake applications, these
valves were used to automatically reduce application
pressure to the front axle brakes. As brake application
pressure was increased, the percentage of reduction
was decreased until approximately 60 psi (depending
upon valve design) full pressure was delivered.
Bendix
®
QR-1C
®
Quick Release Valve
Bendix
®
QRN
™
Quick Release
Valve
Bendix
®
QR-1
®
Quick
Release Valve
Bendix
®
QR-L
™
Inline Quick
Release Valve
Bendix
®
R-7
™
Modulating Valve
The Bendix
®
R-7
™
Modulating Valve is used in dual circuit
brake systems and performs four functions: during normal
operation, it limits hold-off pressure to the spring brakes; it
provides quick release of air pressure from the spring cavity
Bendix
®
R-7
™
Modulating Valve
Spring Brake Actuator
Bendix
®
R-7
™
Modulating Valve
Park
Control
Valve
of the spring brake actuator allowing
a fast application of the spring brake
actuators; it modulates spring brake
actuator application should a failure
occur in the service brake system;
and it prevents compounding of
service and spring forces.
Bendix
®
LQ-4
™
Front Axle Ratio
Valve