Troubleshooting guide

21
www.bendix.com 1-800-AIR-BRAKE (1-800-247-2725)
Quick Release, Ratio Valves
Quick Release Valves
The function of the quick release valve is to speed
up the exhaust of air from the air chambers. It is
mounted close to the chambers it serves. In its standard
configuration, the valve is 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.
Several styles of quick release valves are available and
are functionally the same. The QRV
™
quick release
valve is the oldest design and utilizes a die cast metal
body with an internal diaphragm, spring and spring seat.
The QR-1
™
quick release valve also has a die cast
body and diaphragm, but does not employ a spring or
spring seat. The (non-serviceable) QRN-2
™
quick
release valve is a nonmetallic version of the QR-1
™
quick release valve. The QR-L
™
quick release
valve is an inline device.
QRV
™
Quick
Release Valve
QRN-2
™
Quick
Release Valve
QR-1
™
Quick
Release Valve
QR-L
™
Inline
Quick
Release Valve
Ratio Valves
The LQ-4
™
ratio valve was designed to replace the
LQ-2
™
limiting and quick release valve in the front axle
delivery line of vehicles meeting government
regulations, such as FMVSS 121. During normal service
brake applications, the LQ-4
™
ratio valve automatically
reduces application pressure to the front axle brakes,
however, as brake application pressure is increased the
percentage of reduction is decreased until at
approximately 60 psi (depending upon valve design) full
pressure is delivered. The valve is available with several
different "hold-off" pressures which prevent the front
brakes from operating until the "hold-off" pressure is
exceeded.
The obsolete LQ-3
™
ratio valve appears identical to
the LQ-4
™
ratio valve with minor differences in porting
size.
LQ-4
™
Valve
LQ-4
™
Ratio
Valve