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Bendix® PR-2™, PR-3™ & PR-4™ Pressure Protection Valves
SD-03-2010
DESCRIPTION
The pressure protection valve is a normally closed, pressure
control valve which can be referred to as a non-exhausting
sequence valve. These valves are used in many different
applications. An example would be in an air brake system
to protect one reservoir, or reservoir system from another,
by closing automatically at a preset pressure should a
reservoir system failure occur. The valves can also be used
to delay filling of auxiliary reservoirs to insure a quick build-up
of brake system pressure.
The PR-2
™
and PR-4™ pressure protection valves have one
1/4" N.P.T .F. supply port and one 1/4" N.P .T.F . delivery port
which are identified. Both valves are provided with two 9/32"
mounting holes through the body . The closing pressure of
™
the PR-2
valve is externally adjustable while the PR-4
valve has a fixed setting.
SPRING
CAP
INLET
VALVE
SUPPLY
PORT
PISTON
CHECK
VALVE
DELIVERY
PORT
™
™
PR-3
OR PR-4™ PRESSURE PROTECTION VALVES
SPRING
SUPPLY
PORT
PR-4™ PRESSURE PROTECTION VALVE
CAP
INLET
VALVE
PISTON
DELIVERY
PORT
SUPPLY
PORT
™
PRESSURE PROTECTION VALVE
PR-3
PRESSURE
REGULATING
SPRING
EXHAUST
VENT
PISTON
O-RING
PISTON
SPRING
RETAINER
INLET
VALVE
™
PR-2
PRESSURE PROTECTION VALVE
PISTON PLUG
PISTON PLUG
O-RING
VALVE STEM
INLET
VALVE SPRING
DELIVERY
PORT
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OPERATION
Air entering the supply port is blocked from flowing out the
delivery port by the inlet valve, which is normally held closed
by the pressure regulating spring above the piston. When
sufficient air pressure builds beneath the piston, the piston
will move, opening the inlet valve and allowing air to flow out
the delivery port. As long as air pressure at the supply port
remains above the specified closing pressure, the inlet valve
will remain open.
NOTE: The PR-2™ and PR-4™ valves closing pressure is
noted on the label affixed to the valve. Opening
pressures of the valves are higher than closing
pressures. The pressure ranges are noted below:
PR-2™ valve Opening pressure 15-20 psi higher than
closing pressure.
3. Observing the gauges on the supply and delivery sides
of the valve, slowly exhaust pressure from the delivery
side. Note that both gauges will show pressure loss until
the closing pressure of the pressure protection valve is
reached.
The pressure protection valve should close at
approximately (± 5 psi) the pressure indicated on the
valve’s label or in the vehicle handbook. The gauge on
the delivery side of the valve should continue to show
loss of pressure while the gauge on the supply side
should stop at the same pressure as the setting of the
valve.
4. (PR-3™ valve only) Build pressure up again and shut off
engine. Slowly exhaust air from the supply side of the
PR-3™ valve. The gauge on the delivery side of the valve
should remain at the highest pressure previously attained.
PR-3™ & PR-4™ valves Opening pressure approx.
10 psi higher than closing pressure.
PR-3™ valve Check valve will retain maximum
pressure in downstream reservoir.
If system air pressure decreases below the specified closing
pressure, the regulating spring will close the inlet valve. The
remaining air pressure at either the supply or delivery side,
(depending on where the pressure drop occurs) will be
retained.
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 PR valves
should be inspected every 6 months or 1500 operating hours,
whichever comes first, for proper operation. Should the PR
valves 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 CHECKS
LEAKAGE CHECKS
1. Charge the air system to full pressure and shut off the
engine.
2. Apply a soap solution around the cap of the pressure
protection valve. A 1” bubble in 3 seconds or longer is
acceptable. PR-3™ valve - No leakage is permissible at
the bottom of the valve.
3. Drain the air pressure from the delivery side of the
pressure protection valve and disconnect the air line to
it.
4. Apply a soap solution to the delivery port. A 1” bubble in
5 seconds or more is acceptable.
GENERAL
If the pressure protection valve does not function as
described, or leakage is excessive, it is recommended that
it be replaced with a new or remanufactured unit or repaired
with genuine Bendix parts available at Bendix outlets.
REMOVING AND INSTALLING
REMOVING
1. Block or hold the vehicle by means other than air brakes.
2. Drain all system reservoirs to 0 psi.
3. Disconnect and identify (supply and delivery) the air
lines leading to and from the pressure protection valve.
4. Remove the mounting bolts, if any , that secure the valve.
OPERA TING CHECKS
1. Provide a pressure gauge and drain valve at the supply
side and delivery side of the pressure protection valve
being checked.
2. Charge the air system to full pressure and shut off the
engine.
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INSTALLING
1. Re-install the mounting bolts and secure the replacement
valve to the vehicle.
2. Reconnect the supply delivery air lines to the proper
ports of the replacement valve.
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GENERAL
After installing a replacement valve, it is recommended that
the operating and leakage checks be performed as outlined
in this manual. If the closing pressure does not conform to
that shown on the valve label or in the vehicle or a different
™
setting is desired, the PR-2
valve may be adjusted by
loosening the locknut and tightening or loosening the
adjusting cap as required; however, if the proper setting
cannot be attained by moderate adjustment of the cap, the
valve may have the wrong spring and will have to be
exchanged for the correct valve. The PR-3
™
and PR-4™ valves
are not adjustable.
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
general precautions should be observed at all times.
1. Park the vehicle on a level surface, apply the
parking brakes, and always block the wheels.
Always wear safety glasses.
2. Stop the engine and remove 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.
4. 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 an AD-IS
air dryer system or a dryer reservoir module, be
sure to drain the purge reservoir .
5. Following the vehicle manufacturer’s
recommended procedures, deactivate the electrical
system in a manner that safely removes all
electrical power from the vehicle.
6. Never exceed manufacturer’s recommended
pressures.
7. Never connect or disconnect a hose or line
containing pressure; it may whip. Never remove a
component or plug unless you are certain all
system pressure has been depleted.
8. Use only genuine Bendix
®
replacement parts,
components and kits. Replacement hardware,
tubing, hose, fittings, etc. must be of equivalent
size, type and strength as original equipment and
be designed specifically for such applications and
systems.
9. 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.
10. Prior to returning the vehicle to service, make
certain all components and systems are restored
to their proper operating condition.
®
3. 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.
1 1 . For vehicles with Antilock T raction Control (ATC),
the ATC function must be disabled (A TC 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.
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BW1440 © 2006 Bendix Commercial Vehicle Systems LLC. All rights reserved. 7/2006 Printed in U.S.A.
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