Bendix dryer troubleshooting

Bendix DRM dryer Reservoir troubleshooting

1. Dryer is constantly “cycling" or purging.A. Excessive system leakage.A. Test for excessive system leakage.
Allowable leakage observed at dash gauge:
Single vehicle -1 psi/minute.
Tractor trailer 3 psi/minute.
Using soap solution, test vehicle for leakage at fittings, drain valves and system valves. Repair or replace as necessary.
B. Defective delivery check valve.B. Build system pressure to governor cut-out. Wait 1 minute for completion of purge cycle. Using soap solution at exhaust of purge valve, leakage should not exceed a 1" bubble in less than 5 seconds.
If a rapid loss of pressure is found, the following procedure will determine if the delivery check valve is malfunctioning:
Build system pressure to governor cut-out and allow a full minute for the normal dryer purge cycle to empty the purge reservoir. Switch off the engine and fan" the brakes so that the system pressure reaches governor cut-in. The purge valve will return to its closed position. The purge reservoir has a drain valve which is opened by moving the center lever away from its closed position. Open the drain valve and wait 10 seconds to allow any residual purge pressure to be released. Release the lever, closing the drain valve. Carefully remove the air dryer cartridge using a strap wrench and then test for air leaking through the center of the threaded boss by applying a soap solution to the boss. Replace the delivery check valve if there is excessive leakage (exceeding a 1” bubble in 5 seconds).
Regrease the seal on the air dryer cartridge before reinstalling. Be sure the drain valve on the purge reservoir is not leaking before restoring vehicle to service.
C. Defective governor.C. Check governor at both “cut-in" and “cut-out" position for (i) proper pressures and (ii) excessive leakage at fittings and exhaust.
D. Compressor unloader mechanism leaking excessively.D. Remove air strainer or fitting from compressor inlet cavity. With compressor unloaded, check for unloader piston leakage. Slight leakage permissible.
2. Water in vehicle reservoirs.A. Maximum air dryer inlet temperature is exceeded due to improper discharge line length.A. Check for excessive carbon build up in compressor discharge line. Replace if required. Make certain that discharge line length is at least 6 ft. Increase discharge line length and/or diameter to reduce air dryer inlet temperature.
B. Air system charged from outside air source (outside air not passing through air dryer).B. If system must have outside air fill provision, outside air should pass through air dryer.
C. Excessive air usage Air dryer not compatible with vehicle air system requirement (Improper air dryer/vehicle application).C. Note: The AD-IS® air dryer is not intended for use on applications with excessive air usage. The following applications require more dry air than the AD-IS* air dryer is designed to supply. Do not use on:
1) City buses.
2) Vehicle combinations with more than 8 braked axles.
3) City refuse vehicles except those with work brakes.
4) Concrete mixers.
5) Dump trucks with more than 3 axles.
6) Off-highway/construction vehicles with more than 7 braked axles.
7) Vehicles with compressor on times in excess of 20%.
If the vehicle is equipped with high air usage accessories such as trailer pump-off systems or central tire inflation, the air for these accessories must by-pass the dryer.
D. Desiccant requires replacement.D. Replace desiccant cartridge assembly.
E. Air by-passes desiccant cartridge assembly.E. If vehicle uses Holset compressor, inspect feedback check valve for proper installation and operation.
F. Air dryer not purging.F. Refer to Symptom 6.
G. Purge (air exhaust) time insufficient due to excessive system leakage.G. Refer to Symptom 1.
3. Safety valve on air dryer “popping off” or exhausting air.A. DefectiveAD-IS* air dryer delivery check valve.A. Test to determine if air is passing through check valve. Repair or replace. Refer to Symptom 1, Remedy B.
B. System pressure too high (>135 p.s.i.)B. Test with accurate gauge. Replace governor if necessary.
C. Excessive pressure pulsations from compressor. (Typical single cylinder type).C. Increase volume in discharge line. This can be accomplished by adding a 90 cubic inch (or larger) reservoir between the compressor and the AD-IS® air dryer.
D. Safety valve setting too low (<150 p.s.i.)D. Replace safety valve.
4. Constant exhaust of air at air dryer purge valve exhaust or unable to build system pressure. (Charge mode.)A. Air dryer purge valve leaking excessively.A. With compressor loaded, apply soap solution on purge valve exhaust, to test for excessive leakage. Repair or replace purge valve as necessary.
B. Purge valve frozen open faulty heater and thermostat, wiring, blown fuse.B. Refer to paragraph 5 of Operation and Leakage Tests for heater and thermostat test.
C. Defective AD-IS® air dryer delivery check valve.C. Refer to Symptom 1. Remedy B.
D. Leaking Turbo Cutoff valve.D. Repair or replace purge valve assembly.
E. Defective governor.E. Check governor at both “cut-in" and “cut-out" position for (i) proper pressures and (ii) excessive leakage at fittings and exhaust.
F. Leaking purge valve control piston quad-ring.F. Repair or replace purge valve assembly.
5. Can not build system air pressure.A. Kinked or blocked (plugged) discharge line.A. Check to determine if air passes through discharge line. Check for kinks, bends, excessive carbon deposits, or ice blockage.
B. Excessive bends in discharge line (water collects and freezes).B. Discharge line should be constantly sloping from compressor to air dryer with as few bends as possible.
C. Pressure protection valve(s) in air dryer will not open.C. Replace air dryer (pressure protection valves are not serviceable).
D. Refer to Symptom 4.D. Refer to Symptom 4, Remedy A.
E. Refer to Symptom 7.E. Refer to Symptom 7. Remedies A through D.
6. Air dryer does not purge or exhaust air.A. Faulty air dryer purge valve.A. After determining air reaches purge valve control port by installing a T-fitting with a pressure gauge into the governor unloader port, repair purge valve if necessary.
B. See Causes, B, E, and G for Symptom #4.B. Refer to Symptom 4, Remedies B, E. and G Also refer to Symptom 1. Remedy B.
7. Desiccant material being expelled from air dryer purge valve exhaust (may look like whitish liquid or paste or small beads.)A. Faulty dryer cartridge.A. Replace AD-IS® air dryer cartridge and/or AD-IS* air dryer.
B. Excessive dryer vibration.B. Check reservoir mounting for looseness or damage. Repair mounting and replace cartridge.
8. Unsatisfactory desiccant life.A. Excessive system leakage.A. Refer to Symptom 1. Remedy A.
B. Wrong vehicle application for AD-IS* air dryer.B. Refer to Symptom 2, Remedy C.
C. Compressor passing excessive oil.C. Check for proper compressor installation; if symptoms persist, replace compressor. Refer to Bendix Advanced Troubleshooting Guide for Air Brake Compressors (BW1971).
9. “Pinging" noise excessive during compressor loaded cycle.A. Single cylinder compressor with high pulse cycles.A. A slight “pinging" sound may be heard during system build up when a single cylinder compressor is used. If this sound is deemed objectionable, it can be reduced substantially by increasing the discharge line volume.
This can be accomplished by adding a 90 cubic inch reservoir between the compressor and the AD-IS* air dryer.