Bendix Commercial Vehicle Systems PRESSURE PROTECTION VALVES User Manual

Bendix® PR-2™, PR-3™ & PR-4™ Pressure Protection Valves

SD-03-2010

™

PR-3

PRESSURE PROTECTION

OR PR-4™

VALV ES

PR-2™ PRESSURE

PROTECTION VALVE

CAP

INLET

VALV E

SUPPLY

PORT

SUPPLY

PORT

SPRING

PISTON

CHECK

VALV E

PRESSURE

REGULATING

SPRING

EXHAUST

VENT

PISTON O-RING

PISTON

SPRING

RETAINER

INLET

VALV E

DELIVERY

PORT

SUPPLY

PORT

BENDIX® PR-4™ PRESSURE PROTECTION VALVEBENDIX® PR-3™ PRESSURE PROTECTION VALVE

SPRING

PISTON PLUG

VALVE STEM

CAP

PISTON

INLET

VALV E

DELIVERY

PORT

O-RING

INLET

VALVE SPRING

BENDIX

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

DELIVERY

PORT

PR-2™ PRESSURE PROTECTION VALVE

be used to delay ﬁ lling of auxiliary reservoirs to ensure a quick build-up of brake system pressure.

The Bendix

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 identiﬁ ed. Both valves are provided with two 9/32” mounting holes through the body. The closing pressure of the PR-2

™

the PR-4

valve has a ﬁ xed setting.

™

valve is externally adjustable while

OPERATION

Air entering the supply port is blocked from ﬂ owing out the delivery port by the inlet valve, which is normally held closed by the pressure regulating spring above the piston. When sufﬁ cient air pressure builds beneath the piston, the piston will move, opening the inlet valve and allowing air to ﬂ ow out the delivery port. As long as air pressure at the supply port remains above the speciﬁ ed closing pressure, the inlet valve will remain open.

NOTE: The Bendix

pressure is noted on the label afﬁ xed to the valve. Opening pressures of the valves are higher than closing pressures. The pressure ranges are noted below:

Bendix® PR-2™ valve - Opening pressure 15-20 psi higher than closing pressure.

PR-2™ and PR-4™ valves closing

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.

Bendix® PR-3™ & PR-4™ valves - Opening pressure approximately 10 psi higher than closing pressure.

Bendix® PR-3™ valve - Check valve will retain maximum pressure in downstream reservoir.

If system air pressure decreases below the speciﬁ ed 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 ﬁ rst, 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

OPERATING 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.

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.

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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