SERVICE MANUALIt is important that this valve be installed when anyauxiliary attachments are installed on a vehicle to avoidcomplete loss of air in the event of an air leak in any ofthe air operated attachments.Fig. 4 Pressure Protection ValveOPERATIONAs long as the air supply pressure is below 448-517kPa (65-75 psi) the spring will hold the diaphragm on itsseat restricting the air flow through the valve.When the air supply pressure overcomes the springforce, the diaphragm will move off the seat and allow airto flow through the valve and to the auxiliary equipmentused on the vehicle.If air pressure should fall approximately 138 kPa (20psi) below the opening pressure, the spring force willovercome the air pressure and force the diaphragm onit’s seat closing off the air supply, protecting the airsystem from a complete loss of air through usage of theauxiliary equipment.MAINTENANCEOnce each year or 160,000 km (100,000 miles)remove the pressure protection valve, disassemble it andclean all parts.Replace the diaphragm if it is worn or deteriorated.SERVICE CHECKSBe sure the vent hole is not obstructed.Bleed off main air supply.Disconnect the air outlet side of valve, apply an airpressure gauge known to be accurate with a shut-offvalve. Start engine and allow air pressure to build up.Observe gauge on instrument panel and at valve outlet.You should not have air pressure at test gauge untilmain air reservoir pressure reaches 448-517 kPa (65-75psi). Then the pressure protection valve opens and bothtest gauge and gauge on vehicle should recordapproximately the same.Stop engine and open the shut-off valve at testgauge. Air should exhaust until air pressure on vehiclereaches a pressure at approximately 138 kPa (20 psi)below opening pressure then stop. If the valve performsas described the valve is functioning properly.Bleed off main air reservoir pressure and removeshut-off valve and test gauge. Reconnect line to theauxiliary equipment.REMOVEBe sure to bleed off air reservoir pressure.Disconnect air line routed to auxiliary fixture.Remove pressure protection valve from connector.REINSTALLInstall the pressure protection valve on same fitting valveas was removed. Connect air line routed to auxiliaryfixture.Build up air supply and check connections for air leaks.DISASSEMBLY (Refer to Fig. 5)1. Remove the four screws retaining upper and lowerbody sections together. Care must be taken whileremoving screws as the spring force will separate theupper and lower bodies. MT-20968Fig. 5 Cross Section of Pressure Protection Valve1Vent Hole5Lower Body2Upper Body6Spring Cap3Diaphragm7Spring4Air Flow8ShimCTS-4079-CHAPTER IIIPRINTED IN UNITED STATES OF AMERICAPage 5
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