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Bendix® TU-FLO® 400, 500, 1000 Air Compressors
SD-01-326
TU-FLO® 400 Air Compressor |
TU-FLO® 500 Air Compressor |
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TU-FLO® 1000 Air Compressor
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DESCRIPTION AND OPERATION
GENERAL
The function of the air compressor is to build up and maintain the air pressure required to operate air powered devices in air brake or air auxiliary systems.
DESCRIPTION
Tu-Flo® Type 400, 500, and 1000 compressors are single stage, reciprocating piston type compressors. Tu-Flo® 400 (Fig. 1) and 500 (Fig. 2) compressors have two cylinders while the Tu-Flo® 1000 compressor (Fig. 3) is a V-type design having four cylinders. The rated capacity of all Bendix compressors is their piston displacement in cubic feet per minute when operating at 1,250 RPM. The rated capacity of the Tu-Flo® 400 compressor is 7-1/4 cubic feet per minute. The Tu-Flo® 500 compressor is rated at 12 cubic feet per minute and the Tu-Flo® 1000 compressor has a rating of 24 cubic feet per minute.
Tu-Flo® type compressors have automatic type inlet valves. Their unloading mechanisms are located in the cylinder block
and they have no external moving parts. Both air and water cooled type compressors are available. Various mounting and drive adaptations are used as required by different vehicle engine designs (Fig. 4).
FIGURE 1 - TU-FLO® 400 AIR COMPRESSOR
FIGURE 2 - TU-FLO® 500 AIR COMPRESSOR
FIGURE 3 - TU-FLO® 1000 AIR COMPRESSOR
FIGURE 4 - VARIOUS COMPRESSOR MOUNTINGS
Compressors are either engine or self-lubricated. The majority used are the engine lubricated types (Fig. 5) which obtain the oil necessary to lubricate their moving parts from the engines on which they are mounted. To meet the requirements of some manufacturers and for field installations, self-lubricated types (Fig. 6) are available. They are compressors having a self-contained oil supply and pumping system.
The method of lubricating the moving parts of the compressor is the same in either type. Oil is forced through the oil passage in the crankshaft and out around each connecting rod journal. The turning motion of the crankshaft throws the oil that is forced out at the journals, against the cylinder bores and crankcase walls, lubricating the bores and crankshaft bearings.
The wrist pins and wrist pin bushings are lubricated in two ways depending upon the type connecting rods used. Older design compressors had forged steel rifle-drilled rods through which oil was forced to the wrist pin bushings. Later versions
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FIGURE 5 |
FIGURE 6 |
ENGINE LUBRICATED TYPE |
SELF-LUBRICATED TYPE |
had either die cast aluminum, cast ductile iron, or forged steel rods which were not rifle drilled but were drilled at the top of the rod. The wrist pins and bushings are lubricated by oil dripping from a drip-boss on the piston into a “catch-funnel” at the top of the rod and through the drilled passage to the bushings and pins. (SEE FIG. 7)
PISTON WRIST PIN |
WRIST PIN |
LOCK WIRE |
BUSHING |
WRIST PIN |
CAST IRON |
PISTON |
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OIL |
STEEL |
PASSAGE |
CONNECTING |
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ROD |
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OLD DESIGN |
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“CATCH FUNNEL” |
WRIST PIN |
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BUSHING |
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DIE CAST |
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PISTON |
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DIE CAST |
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CONNECTING ROD |
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NEW DESIGN |
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FIGURE 7- PISTONS & CONNECTING RODS
A nameplate is attached to the crankcase of all compressors. It shows the piece number, type and serial number (Fig. 8). A nameplate with a black background denotes a new compressor, whereas a nameplate with a red background designates that the compressor is a factory reconditioned unit. All compressors are identified by the piece number which is the number to use when reference is made to a particular compressor. The type and serial number is supplementary information.
FIGURE 8 - COMPRESSOR NAMEPLATE
OPERATION
GENERAL
All compressors run continuously while the engine is running, but actual compression of air is controlled by a governor, which stops or starts the compression of air by loading or unloading the compressor in conjunction with its unloading mechanism. This is done when the air pressure in the system reaches the desired maximum or minimum pressures.
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TO RESERVOIR |
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DISCHARGE |
INLET VALVE |
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UNLOADER PLUNGER |
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VALVE |
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PISTON |
INTAKE |
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STRAINER |
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TO GOVERNOR |
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STROKE |
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INTAKE |
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FIGURE 9 |
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INTAKE AND COMPRESSION (Loaded)
During the down stroke of the piston, a slight vacuum created above the piston causes the inlet valve to move off its seat. Atmospheric air is drawn in through the compressor intake, by the open inlet valve, and on top of the piston (Fig. 9). As the piston starts its upward stroke, the air that was drawn in on the down stroke is being compressed. Now, air pressure on top of the inlet valve plus the force of its spring, returns the inlet valve to its seat. The piston continues the upward stroke and compresses the air sufficiently to overcome the discharge valve spring and unseat the discharge valve. The compressed air then flows by the open discharge valve, into the discharge line and on to the reservoirs (Fig. 10).
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TO RESERVOIR |
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DISCHARGE |
INLET VALVE |
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UNLOADER PLUNGER |
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VALVE |
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PISTON |
INTAKE |
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STRAINER |
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TO GOVERNOR |
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STROKE |
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COMPRESSION |
FIGURE 10
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As the piston reaches the top of its stroke and starts down, the discharge valve spring returns the discharge valve to its seat. This prevents the compressed air in the discharge line from returning to the cylinder bore as the intake and compression cycle is repeated.
NON-COMPRESSION (Unloaded)
When the air pressure in the reservoir reaches the high pressure setting of the governor, the governor opens, allowing air to pass from the reservoir through the governor and into the cavity beneath the unloader pistons. This lifts the unloader pistons and plungers. The plungers move up and hold the inlet valves off their seats (Fig. 11).
DISCHARGE |
TO RESERVOIR |
INLET VALVE |
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VALVE |
UNLOADER |
PISTON |
PLUNGER |
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INTAKE |
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STRAINER |
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TO GOVERNOR |
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STROKE |
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UNLOADING |
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FIGURE 11 |
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With the inlet valves held off their seats by the unloader pistons and plungers, air is merely pumped back and forth between the two cylinders. When air is used from the reservoir and the pressure drops to the low pressure setting of the governor, the governor closes, and in doing so, exhausts the air from beneath the unloader pistons. The unloader saddle spring forces the saddle, pistons and plungers down and the inlet valves return to their seats. Compression is then resumed.
COMPRESSOR & THE AIR BRAKE SYSTEM
GENERAL
The compressor is part of the total air brake system, more specifically, the charging portion of the air brake system. As a component in the overall system its condition, duty cycle, proper installation and operation will directly affect other components in the 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 system, lubricated by the engine oil supply and has its inlet connected to the engine induction system.
As the atmospheric air is compressed, all the water vapor originally in the air is carried along into the air system, as well as a small amount of the lubricating oil as vapor. If an air dryer is not used to remove these contaminants prior to
entering the air system, the majority, but not all, will condense in the reservoirs. The quantity of contaminants that reach the air system depends on several factors including installation, maintenance and contaminant handling devices in the system. These contaminants must either be eliminated prior to entering the air system or after they enter.
DUTY CYCLE
The duty cycle is the ratio of time the compressor spends building air to the total engine running time. Air compressors are designed to build air (run "loaded") up to 25% of the time. Higher duty cycles cause conditions that affect air brake charging system performance which may require additional maintenance. Factors that add to the duty cycle are: air suspension, additional air accessories, use of an undersized compressor, frequent stops, excessive leakage from fittings, connections, lines, chambers or valves, etc. Refer to Table A in the Troubleshooting section for a guide to various duty cycles and the consideration that must be given to maintenance of other components.
COMPRESSOR INSTALLATION
While the original compressor installation is usually completed by the vehicle manufacturer, conditions of operation and maintenance may require additional consideration. The following presents base guidelines.
DISCHARGE LINE
The discharge line allows the air, water-vapor and oil-vapor mixture to cool between the compressor and air dryer or reservoir. The typical size of a vehicle's discharge line, (see column 2 of Table A in the Troubleshooting section) assumes a compressor with a normal (less than 25%) duty cycle, operating in a temperate climate. See Bendix and/or other air dryer manufacturer guidelines as needed.
The discharge line must maintain a constant slope down from the compressor to the air dryer inlet fitting or reservoir to avoid low points where ice may form and block the flow. If, instead, ice blockages occur at the air dryer or reservoir inlet, insulation may be added here, or if the inlet fitting is a typical 90 degree fitting, it may be changed to a straight or 45 degree fitting. Shorter discharge line lengths or insulation may be required in cold climates.
While not all compressors and charging systems are equipped with a discharge line safety valve this component is recommended. The discharge line safety valve is installed in the cylinder head or close to the compressor discharge port and protects against over pressurizing the compressor in the event of a discharge line freezeup.
DISCHARGE LINE TEMPERATURE
When the temperature of the compressed air that enters the air dryer is within the normal range, the air dryer can remove most of the charging system oil. If the temperature of the compressed air is above the normal range, oil as oilvapor is able to pass through the air dryer and into the air system. Larger diameter discharge lines and/or longer discharge line lengths can help reduce the temperature.
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Discharge |
Optional “Ping” Tank |
Line |
Air Dryer |
Compressor
Governor
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 ® QC™
Oil Coalescing Filter
(Governor plus Synchro valve |
Service Reservoir |
for the Bendix® DuraFlo™ 596 |
(Supply Reservoir) |
Compressor) |
Reservoir Drain |
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FIGURE 12A - SYSTEM DRAWING |
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HOLE
THREAD
FIGURE 12B - DISCHARGE LINE SAFETY VALVE
The air dryer contains a filter that collects oil droplets, and a desiccant bed that removes almost all of the remaining water vapor. The compressed air is then passed to the air brake service (supply) reservoir. The oil droplets and the water collected are automatically purged when the governor reaches its "cut-out" setting.
For vehicles with accessories that are sensitive to small amounts of oil, we recommend installation of a Bendix® PuraGuard® QC™ oil coalescing filter, designed to minimize the amount of oil present.
COOLING
Tu-Flo® 400, 500 or 1000 compressors may be air-cooled or watercooled and in some instances will have air-cooled blocks and water-cooled heads. The air-cooled versions are easily recognized by the external fins. The water-cooled versions are cooled by vehicle coolant.
PREVENTIVE MAINTENANCE
Regularly scheduled maintenance is the single most important factor in maintaining the air brake charging system. Refer to Table A in the Troubleshooting section for a guide to various considerations that must be given to the maintenance of the compressor and other related charging system components.
If the compressor is a self-lubricated type, its oil level should be checked daily. The oil level should be kept between the bottom of the dipstick threads and the bottom of the dipstick (Fig. 13). Every 8,000 miles or 300 operating hours, the oil should be drained and refilled with SAE 10-20-30.
FIGURE 13 - OIL LEVEL - SELF-LUBRICATED
COMPRESSOR
POLYURETHANE SPONGE STRAINER (Fig. 14)
Remove and wash all of the parts. The strainer element should be cleaned or replaced. If the element is cleaned, it should be washed in a commercial solvent or a detergent and water solution. The element should be saturated in clean engine oil, then squeezed dry before replacing it in the strainer. Be sure to replace the air strainer gasket if the entire air strainer is removed from the compressor intake.
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