SD-03-905

®

Bendix® QRN™ Quick Release Valve
MOUNTING HOLE (2)

SUPPLY PORT

UPPER BODY
DIAPHRAGM

DELIVERY
PORT

DELIVERY
PORT

LOWER
BODY
SPRING FOLLOWER

INSERT A

EXHAUST PORT

LOCKWASHER
SEALING RING

CAP SCREW

DIFFERENTIAL SPRING
Figure 1 – Bendix® QRN™ Quick Release Valve

DESCRIPTION
The function of the Bendix® QRN™ quick release valve is to
“speed up” the exhaust of air from the actuators it serves. It
is generally mounted on the vehicle axle midway between
the two actuators connected to it.

Various pipe thread sizes are available for the single supply
port and two delivery ports of the QRN valve. Mounting
the valve is accomplished via two 11/32" diameter holes
on 1-1/2" centers.

In the standard (Refer to Figure 1) QRN valve, a flat circular
diaphragm is installed between the nonmetallic upper body
and stamped steel lower body. An o-ring seals the two body
halves which are held together using four 1/4" machine
screws and flange nuts.

OPERATION

In its standard configuration, the QRN valve is supplied with
a 1 psi (6.9 kPa) maximum differential. For example, with
supply pressure at 10 psi (68.9 kPa) delivery pressure is 9
psi (61.8 kPa). Higher differential pressures are available
for special applications and are obtained by the addition
of a spring and diaphragm follower to the standard QRN
valve. Refer to Figure 1 - Insert A.

With no air pressure applied to the QRN valve, the
diaphragm is slightly flexed by the upper and lower body.
In this condition the center portion of the diaphragm rests on
the exhaust port in the lower body while the outer edge and
opposite side of the diaphragm rests against the sealing
lip of the upper body. Refer to Figure 1.

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GENERAL SAFETY GUIDELINES

WARNING! PLEASE READ AND
FOLLOW THESE INSTRUCTIONS
TO AVOID PERSONAL INJURY OR DEATH:

When working on or around a vehicle, the following
guidelines should be observed AT ALL TIMES:
▲Park the vehicle on a level surface, apply the parking
brakes and always block the wheels. Always wear personal
protection equipment.
▲Stop the engine and remove the ignition key when working
under or around the vehicle. When working in the engine
compartment, the engine should be shut off and the ignition
key should be removed. Where circumstances require that
the engine be in operation, EXTREME CAUTION should be
used to prevent personal injury resulting from contact with
moving, rotating, leaking, heated or electrically-charged
components.
▲Do not attempt to install, remove, disassemble or
assemble a component until you have read, and thoroughly
understand, the recommended procedures. Use only the
proper tools and observe all precautions pertaining to use
of those tools.
▲If the work is being performed on the vehicle’s air brake
system, or any auxiliary pressurized air systems, make
certain to drain the air pressure from all reservoirs before
beginning ANY work on the vehicle. If the vehicle is
equipped with a Bendix® AD-IS® air dryer system, a Bendix®
DRM™ dryer reservoir module, or a Bendix ® AD-9si ® air
dryer, be sure to drain the purge reservoir.
▲Following the vehicle manufacturer’s recommended
procedures, deactivate the electrical system in a manner
that safely removes all electrical power from the vehicle.
▲Never exceed manufacturer’s recommended pressures.
▲Never connect or disconnect a hose or line containing
pressure; it may whip and/or cause hazardous airborne
dust and dirt particles. Wear eye protection. Slowly open
connections with care, and verify that no pressure is
present. Never remove a component or plug unless you are
certain all system pressure has been depleted.
▲Use only genuine Bendix ® brand replacement parts,
components and kits. Replacement hardware, tubing, hose,
fittings, wiring, etc. must be of equivalent size, type and
strength as original equipment and be designed specifically
for such applications and systems.
▲Components with stripped threads or damaged parts should
be replaced rather than repaired. Do not attempt repairs
requiring machining or welding unless specifically stated
and approved by the vehicle and component manufacturer.
▲Prior to returning the vehicle to service, make certain all
components and systems are restored to their proper
operating condition.
▲For vehicles with Automatic Traction Control (ATC), the ATC
function must be disabled (ATC indicator lamp should be
ON) prior to performing any vehicle maintenance where
one or more wheels on a drive axle are lifted off the ground
and moving.
▲The power MUST be temporarily disconnected from the
radar sensor whenever any tests USING A DYNAMOMETER
are conducted on a vehicle equipped with a Bendix ®
Wingman ® system.
▲You should consult the vehicle manufacturer's operating
and service manuals, and any related literature, in
conjunction with the Guidelines above.
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APPLY
Air entering the supply port of the Bendix® QRN™ quick
release valve causes the center portion of the diaphragm
to seal the exhaust port. Simultaneously, the outer edge
of the diaphragm moves away from the sealing lip of the
upper body allowing air to flow from the supply port out
the delivery ports.

BALANCE
When air pressure on both sides of the diaphragm
is approximately equal (1 psi differential), the natural
resiliency of the diaphragm material causes the outer
edge of the diaphragm to move into contact with the upper
body sealing lip. The QRN valve exhaust remains sealed
because air pressure bears against the center portion of
the diaphragm from one side only.

RELEASE
When air pressure is reduced or removed from the QRN
quick release valve supply port, the air pressure on the
delivery side of the diaphragm is greater than that on the
supply side. The higher delivery side pressure holds the
outer edge of the diaphragm against the upper body sealing
lip while simultaneously moving the center portion away
from the exhaust port. Air from the delivery ports flows out
the exhaust. When air pressure on the delivery side of the
diaphragm equals the pressure on the supply side, the
center portion of the diaphragm moves into contact with
the exhaust port.

PREVENTIVE MAINTENANCE

IMPORTANT
Review the Bendix Warranty Policy before performing any
intrusive maintenance procedures. A warranty may be
voided if intrusive maintenance is performed during the
warranty period.
No two vehicles operate under identical conditions, as
a result, maintenance intervals may vary. Experience is
a valuable guide in determining the best maintenance
interval for air brake system components. At a
minimum, the QRN valve should be inspected every
12 months or 3600 operating hours, whichever comes
first, for proper operation. Should the QRN valve not
meet the elements of the operational tests noted in
this document, further investigation and service of the
valve may be required.

OPERATING AND LEAKAGE TESTS

1. Apply 100 psi (689 kPa) air pressure to the supply port
of the Bendix® QRN™ quick release valve and note that
the device connected to the valve responds promptly.
2. With 100 psi (689 kPa) air pressure applied to the
QRN valve SUPPLY port, apply a soap solution to the
exhaust port and around the junction of the upper and
lower body halves.
A. No leakage is permitted between the body halves.
B. Leakage of greater than a 1 inch (25.4 mm) bubble
in three seconds at the exhaust port is unacceptable.
3. Release the air pressure at the supply port and note
that the device connected to the QRN valve responds
promptly and returns to a zero air pressure condition.
4. If the QRN valve does not function as described or
if leakage is excessive, it is recommended that it be
replaced with a new or remanufactured unit or repaired
using a genuine Bendix® maintenance kit.
5. Use only genuine Bendix replacement parts and
components.
A. Only components, devices, mounting and attaching
hardware specifically designed should be used.
B. Replacement hardware, tubing, hose, fittings, etc.
should be of equivalent size, type, length, and
strength as the original equipment.
C. Make certain that when replacing tubing or hose, all
supports, clamps or suspending devices that were
originally installed by the vehicle manufacturer are
reinstalled.
6. Devices with stripped threads or damaged parts should
be replaced. Repairs requiring machining should not
be attempted.

REMOVING THE BENDIX® QRN™ VALVE

1. Park the vehicle on a level surface. Block the wheels
and/or hold the vehicle by means other than the air
brakes.
2. Drain all air brake system reservoirs.
3. Identify, mark and disconnect all air lines from the valve.
4. Remove all tubing or hose fittings from the valve.
5. Remove the valve mounting hardware and the valve.

DISASSEMBLY
The following disassembly procedure is provided as a
reference. Before disassembling the QRN valve, a Bendix
maintenance kit or genuine replacement parts should be
available.
1. Remove the four 1/4" flange nuts and bolts that secure
the upper and lower body halves. NOTE: Before
removing the last two nuts and bolts completely, check
the opening between the body halves to determine if
the QRN valve has a differential spring installed. If so,
a light spring load should be anticipated and can be
easily controlled by manually holding the body halves
together.
2. Separate the body halves and remove the diaphragm
(and diaphragm follower and spring if so equipped).
3. Remove the sealing ring between the body halves.

CLEANING & INSPECTION
1. Clean the upper and lower body halves; also the
diaphragm follower and spring (if applicable) in mineral
spirits. Do not immerse nonmetallic components for a
prolonged period of time (no more than 10 minutes).
Dry all parts thoroughly.
2. It is recommended that the diaphragm and sealing ring
be replaced after disassembly.
3. Inspect the upper body for galled threads and cracks.
If found, the entire QRN valve should be replaced.
4. Inspect the interior valve portion of the lower body for
heavy corrosion and pitting. If found, replace the entire
QRN valve assembly.
5. If applicable, inspect the diaphragm follower and spring
for any corrosion and pitting, replace if necessary.

ASSEMBLY
1. Place the supply port of the upper body down on a clean,
level work surface. Install the flat circular diaphragm in
the upper body making certain it is CENTERED.
2. If applicable, install and center the diaphragm follower
with its flat flange side against the diaphragm. Install
the spring on the diaphragm follower.
3. Install the sealing ring on the lower body and carefully
install the lower body on the upper body. Make certain
that the diaphragm remains centered in the upper body
and the sealing ring enters its groove in the upper body.
4. Install the four 1/4" flange nuts and bolts and torque to
60 in-lbs (6.78 Nm).

3

INSTALLING THE BENDIX® QRN™ VALVE
1. Mount the Bendix® QRN™ quick release valve on the
vehicle with the exhaust port pointing down.
2. Install the tubing or hose fittings in the upper body of
the valve. If a thread sealant is used, make certain that
this material will not enter the valve during use.

IMPORTANT
WHEN INSTALLING FITTINGS, DO NOT TORQUE
BEYOND THE FOLLOWING OR DAMAGE TO THE
UPPER BODY MAY RESULT:

12 ft-lbs. (16.3 Nm) for the supply port

10 ft-lbs. (13.6 Nm) for the delivery ports

(or 2-1/2 turns beyond finger tight for each.)

3. Connect the air lines to the valve as identified in Step
4 of "Removing the Bendix® QRN™ Valve".
4. Perform the “Operating and Leakage Tests” before
placing the vehicle in service.

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SD-03-905 Rev. 006 © 2017 Bendix Commercial Vehicle Systems LLC, a member of the Knorr-Bremse Group 01/17 • All rights reserved.