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Advanced Troubleshooting Guide for Air Brake Compressors

*This Guide is only for vehicles that use desiccant air Guide consists of an introduction to air Brake charging systemcomponents, a table showing recommended vehicle maintenanceschedules, and a Troubleshooting symptom and remedy section with teststo diagnose most charging system Troubleshooting Guidefor Air Brake Compressors *This Troubleshooting Guide obsoletes and supersedes all previous publishedtroubleshooting information relative to Bendix air Brake charging system:Slow build ( ) .. 9 - 10 Doesn t build air ( ) .. 11 Air dryer:Doesn t purge ( ) .. 12 Safety valve releases air ( ) .. 12 Compressor:Constantly cycles ( ).

2 Introduction to the Air Brake Charging System Powered by the vehicle engine, the air compressor builds the air pressure for the air brake system. The air compressor is typically cooled by the engine coolant

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Transcription of Advanced Troubleshooting Guide for Air Brake Compressors

1 *This Guide is only for vehicles that use desiccant air Guide consists of an introduction to air Brake charging systemcomponents, a table showing recommended vehicle maintenanceschedules, and a Troubleshooting symptom and remedy section with teststo diagnose most charging system Troubleshooting Guidefor Air Brake Compressors *This Troubleshooting Guide obsoletes and supersedes all previous publishedtroubleshooting information relative to Bendix air Brake charging system:Slow build ( ) .. 9 - 10 Doesn t build air ( ) .. 11 Air dryer:Doesn t purge ( ) .. 12 Safety valve releases air ( ) .. 12 Compressor:Constantly cycles ( ).

2 13 Leaks air ( ) .. 13 Safety valve releases air ( ) .. 11 Noisy ( ) .. 13 Reservoir:Safety valve releases air ( ) .. 12 INDEXAirCoolantEngineOilCompressor leaks coolant ( ) .. 13 Oil consumption ( ) .. 9 Oil Test Card results ( ) .. 4 Oil is present:On the outside of the compressor ( ) .. 5At the air dryer purge/exhaustor surrounding area ( ) .. 5In the supply reservoir ( ) .. 6 - 8At the valves ( ) .. 8At air dryer cartridge ( ) .. 9In the ping tank or compressordischarge aftercooler ( ) .. 9 SymptomPage Number(1) Oil Leakage at Head Gasket .. 14(2) System Leakage .. 14(3) Compressor Discharge and Air Dryer Inlet Temperature.

3 14(4) Governor Malfunction .. 14(5) Governor Control Line .. 15(6) Compressor Unloader .. 15 BASIC Test Information .. 17-20 Test ProceduresMaintenance Schedule and Usage Guidelines (Table A) .. 3 SymptomPage NumberMaintenance & Usage Guidelines2 Introduction to the Air Brake Charging SystemPowered by the vehicle engine , the air compressorbuilds the air pressure for the air Brake system. Theair compressor is typically cooled by the engine coolantsystem and lubricated by the engine oil compressor's unloader mechanism and governor(along with a synchro valve for the Bendix DuraFlo 596 air compressor) control the Brake system airpressure between a preset maximum and minimumpressure level by monitoring the pressure in the service(or supply ) reservoir.

4 When the air pressure becomesgreater than that of the preset cut-out , the governorcontrols the unloader mechanism of the compressorto stop the compressor from building air and alsocauses the air dryer to purge. As the service reservoirair pressure drops to the cut-in setting of the governor,the governor returns the compressor back to buildingair and the air dryer to air drying the atmospheric air is compressed, all the watervapor originally in the air is carried along into the airsystem, as well as a small amount of the lubricating oilas duty cycle is the ratio of time the compressorspends building air to the total engine running Compressors are designed to build air (run loaded )up to 25% of the time.

5 Higher duty cycles causeconditions that affect air Brake charging systemperformance which may require additionalmaintenance. Factors that add to the duty cycle are:air suspension, additional air accessories, use of anundersized compressor, frequent stops, excessiveleakage from fittings, connections, lines, chambers orvalves, discharge line allows the air, water-vapor andoil-vapor mixture to cool between the compressor andair dryer. The typical size of a vehicle's discharge line,(see column 2 of Table A on page 3) assumes acompressor with a normal (less than 25%) duty cycle,operating in a temperate climate.

6 See Bendix and/orother air dryer manufacturer guidelines as the temperature of the compressed air that entersthe air dryer is within the normal range, the air dryer canremove most of the charging system oil. If thetemperature of the compressed air is above the normalrange, oil as oil-vapor is able to pass through the airdryer and into the air system. Larger diameter dischargelines and/or longer discharge line lengths can help reducethe discharge line must maintain a constant slopedown from the compressor to the air dryer inlet fittingto avoid low points where ice may form and block theflow. If, instead, ice blockages occur at the air dryerinlet, insulation may be added here, or if the inlet fittingis a typical 90 degree fitting, it may be changed to astraight or 45 degree fitting.

7 For more information onhow to help prevent discharge line freeze-ups, seeBendix Bulletins TCH-08-21 and TCH-08-22 (seepages 20-22). Shorter discharge line lengths orinsulation may be required in cold air dryer contains a filter that collects oil droplets,and a desiccant bed that removes almost all of theremaining water vapor. The compressed air is thenpassed to the air Brake service (supply) reservoir. Theoil droplets and the water collected are automaticallypurged when the governor reaches its cut-out vehicles with accessories that are sensitive to smallamounts of oil, we recommended installation of aBendix PuraGuard system filter, designed to minimizethe amount of oil DryerReservoir DrainService Reservoir(Supply Reservoir)CompressorGovernor(Governor plus Synchro valvefor the Bendix DuraFlo 596 Compressor)

8 DischargeLineOptional Ping TankOptional Bendix PuraGuard System Filter or PuraGuard QC Oil Coalescing FilterThe Air Brake Charging System supplies thecompressed air for the braking system as well as otherair accessories for the vehicle. The system usuallyconsists of an air compressor, governor, discharge line,air dryer, and service with up to 25% duty cycleFootnotes:1 With increased air demand the air dryer cartridge needs to be replaced more Use the drain valves to slowly drain all reservoirs to zero Allow the oil/water mixture to fully settle before measuring oil To counter above normal temperatures at the air dryer inlet, (and resultant oil-vapor passingupstream in the air system) replace the discharge line with one of a larger diameter and/or longer length.

9 This helps reduce the air's temperature. If sufficient cooling occurs, theoil-vapor condenses and can be removed by the air dryer. Discharge line upgrades are notcovered under warranty. Note: To help prevent discharge line freeze-ups, shorter dischargeline lengths or insulation may be required in cold climates. (See Bendix Bulletins TCH-08-21and TCH-08-22, included in Appendix B, for more information.)5 For certain vehicles/applications, where turbo-charged inlet air is used, a smaller sizecompressor may be Line Air Dryer Reservoir Oil Contents3No. of Spec'd Cartridge Drain at RegularAxlesReplacement1 Schedule2 Drain IntervalHigh Air UseLow Air Double/triple trailer, openhighway coach/RV, (most)pick-up & delivery, yard orterminal jockey, off-highway,construction, loggers, concretemixer, dump truck, fire Line haul single trailerw/o air suspension, air overhydraulic Line haul single trailerwith air suspension,school City transit bus, refuse,bulk unloaders, low boys,urban region coach, centraltire A.

10 Maintenance Schedule and Usage GuidelinesRecom-mendedEveryMonth -Max ofevery 90daysEveryMonthEvery 3 YearsEvery Used for:Column 1 Column 2 Column 3 Column 4 Column 5 Regularly scheduled maintenance is the single most important factor in maintaining the air Brake charging : Compressor and/or air dryerupgrades are recommended in caseswhere duty cycle is greater than thenormal range (for the examplesabove).For Bendix Tu-Flo 550 and 750compressors, unloader service isrecommended every 250,000 testacceptablerange:5 oil unitsper oil carry-overcontrol4 suggestedupgrades:3/4 in. 15 oil carry-overcontrol4 suggestedupgrades:5/8 in.


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