BENDIX TU-FLO 400-500-1000 AIR COMPRESSOR manual Introduction to the Air Brake Charging System

Page 17

Introduction to the Air Brake Charging System

Powered by the vehicle engine, the air compressor

air dryer. The typical size of a vehicle's discharge line,

builds the air pressure for the air brake system. The

(see column 2 of Table A on page 18) assumes a

air compressor is typically cooled by the engine coolant

compressor with a normal (less than 25%) duty cycle,

system and lubricated by the engine oil supply.

operating in a temperate climate. See Bendix and/or

The compressor's unloader mechanism andgovernor

other air dryer manufacturer guidelines as needed.

(along with a synchro valve for the Bendix® DuraFlo

When the temperature of the compressed air that enters

596 air compressor) control the brake system air

the air dryer is within the normal range, the air dryer can

pressure between a preset maximum and minimum

remove most of the charging system oil. If the

pressure level by monitoring the pressure in the service

temperature of the compressed air is above the normal

(or “supply”) reservoir. When the air pressure becomes

range, oil as oil-vapor is able to pass through the air

greater than that of the preset “cut-out”, the governor

dryer and into the air system. Larger diameter discharge

controls the unloader mechanism of the compressor

lines and/or longer discharge line lengths can help reduce

to stop the compressor from building air and also

the temperature.

causes the air dryer to purge. As the service reservoir

The discharge line must maintain a constant slope

air pressure drops to the “cut-in” setting of the governor,

down from the compressor to the air dryer inlet fitting

the governor returns the compressor back to building

to avoid low points where ice may form and block the

air and the air dryer to air drying mode.

flow. If, instead, ice blockages occur at the air dryer

As the atmospheric air is compressed, all the water

inlet, insulation may be added here, or if the inlet fitting

vapor originally in the air is carried along into the air

is a typical 90 degree fitting, it may be changed to a

system, as well as a small amount of the lubricating oil

straight or 45 degree fitting. For more information on

as vapor.

how to help prevent discharge line freeze-ups, see

The duty cycle is the ratio of time the compressor

Bendix Bulletins TCH-08-21 and TCH-08-22 (see

spends building air to the total engine running time.

pages 35-37). Shorter discharge line lengths or

Air compressors are designed to build air (run “loaded”)

insulation may be required in cold climates.

up to 25% of the time. Higher duty cycles cause

The air dryer contains a filter that collects oil droplets,

conditions that affect air brake charging system

and a desiccant bed that removes almost all of the

performance which may require additional

remaining water vapor. The compressed air is then

maintenance. Factors that add to the duty cycle are:

passed to the air brake service (supply) reservoir. The

air suspension, additional air accessories, use of an

oil droplets and the water collected are automatically

undersized compressor, frequent stops, excessive

purged when the governor reaches its “cut-out” setting.

leakage from fittings, connections, lines, chambers or

For vehicles with accessories that are sensitive to small

valves, etc.

amounts of oil, we recommended installation of a

The discharge line allows the air, water-vapor and

Bendix® PuraGuard® system filter, designed to minimize

oil-vapor mixture to cool between the compressor and

the amount of oil present.

Discharge

Optional “Ping” Tank

Line

Air Dryer

The Air Brake Charging System supplies the compressed air for the braking system as well as other air accessories for the vehicle. The system usually consists of an air compressor, governor, discharge line, air dryer, and service reservoir.

Optional Bendix® PuraGuard®

System Filter or PuraGuard®

QCOil Coalescing Filter

Compressor

Governor

(Governor plus Synchro valve

Service Reservoir

for the Bendix® DuraFlo596

(Supply Reservoir)

Compressor)

 

 

Reservoir Drain

 

 

 

 

 

 

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Contents SD-01-326 Description GeneralIntake and Compression Loaded OperationCompressor & the AIR Brake System Polyurethane Sponge Strainer Fig Preventive MaintenanceCooling Installation ENGINE-LUBRICATED Types Removing and InstallingDRY Element Pleated Paper AIR Strainer FIG AIR Leakage TestsRemoving and Disassembly DisassemblyConnecting ROD Assemblies Crankcase Base Plate or AdapterTU-FLO400 AIR Compressor Vertical Mount Engine Lubricated Crankcase FigInspection of Parts CleaningInlet Valves and Seats Crankcase and END CoversCylinder Bores PistonsRepairs Installing Cylinder Block AssemblyInstalling Crankshaft Pistons and Connecting RodsBaseplate Page Tabulated Data InstallationScheduled Maintenance Symptom Number Test ProceduresMaintenance & Usage Guidelines Introduction to the Air Brake Charging System High Air Use Low Air UseOil Test Card Not a valid test Results Symptom What it may indicate What you should doDiscontinue using this test Oil at air dryer purge/exhaust or surrounding area Oil on the Outside of the CompressorMaintenance Oil in Supply or Service Reservoir air dryer installedInsufficient coolant flow Oil in SupplyOil in Supply or Service Reservoir Or compressor dis Oil in ping tankCharge aftercooler Air brake Charging systemAir brake charging system seems slow to build pressure Releases air Compressor builds too much air Time Air dryer Safety valve releases airNoisy Leaks coolant Coolant line fittingsAction Test 2 Air Brake System and Accessory LeakageTest 1 Excessive Oil Leakage at Head Gasket Test 6 Compressor Unloader Leakage Test 4 Governor MalfunctionTest 5 Governor Control Line Page Appendix a Information about the Basic Test Kit Bendix P/N Bendix Air System Inspection Cup Basic Test InformationStep B Measure the Charging System Contents Checklist for TechnicianStep a Select one Is foundStep D Air Brake System Leakage Test Typical P&D, School Bus and Line Haul Technical BulletinSystem Leakage Thawing Frozen Air Lines Page