Compressor Discharge Line

Additional Information


Installation guidelines for Allied Signal®-Bendix® air compressor are as follows:‪

Compressor Discharge Line

Avoid installing valves (pressure regulator valves, etc.) in the compressor discharge line between the compressor, and reservoir or air dryer. The valves can trap water and lead to discharge line freeze-up during cold temperature conditions. The longer the discharge line length, the greater the potential for a frozen discharge line to occur. Compressor discharge line lengths are listed in Table "Discharge Line Length and Diameter (Low Duty Cycle Applications)" . ‪


I.D. MIN.‪

1.83 - 2.90 m (6.0-9.5 ft)‪

2.90 m - 3.66 m (9.5-12 ft)*‪

2.90 m - 3.66 m (9.5-12 ft)*‪

12.7 mm (0.50 in.)†‪

3.66 - 4.88 m (12-16 ft)*‪

15.88 mm (0.625 in.)‪

Table 1. Discharge Line Length and Diameter (Low Duty Cycle Applications)

* Last three feet including reservoir or air dryer supply port fitting must be insulated with 1/2 in. thick closed cell polyethylene pipe insulation.
† Use of larger I.D. discharge line will further reduce the chances of freeze-up in extreme cold weather conditions and should be considered for "cold weather package" applications.

Note: High duty cycle application with lengths of 3.05 - 4.88 m (10.0 - 16.0 ft) should use a 12.7 mm (0.5 in.) I.D. discharge line.

Note: If the actual application requires the discharge line length to fall outside the specified ranges given, it is recommended that Allied Signal® TBS Engineering department be contacted.

Discharge Line Material

If a copper discharge line is used, a flexible connection to the first reservoir or air dryer should be added to prevent fatigue of the copper line. Wire-braided Teflon® hose must have a minimum operating temperature of 232°C (450°F) and a working pressure of 10.0 bar (150 psi) if connected directly to the compressor discharge fitting.‪

Discharge Line Slope

The discharge line should slope continuously downward from the air compressor discharge port, with no sharp bends, water traps, risers or elbow fittings, to the first reservoir or air drying device. If there are any upward or downward deviations, the line can trap water, which can freeze during cold weather, causing a blockage. Compressor damage can occur as a result of a blocked discharge line.‪

Carbon Restricted Discharge Line

If the discharge line becomes restricted with carbon, the compressor must work harder to deliver compressed air, thus reducing compressor durability. Make sure the discharge line does not have a carbon restriction.‪

Discharge Line Accessories

The application of a downstream device such as an air dryer, discharge line unloader, or turbocharger cut-off valve, needs to be installed properly to avoid premature compressor durability problems. Refer to the manufacturer's instructions for these products. ‪

Note: Alcohol injectors which restrict the flow of air in the discharge line should be avoided. Restrictions in the discharge line increase the time required to build up system pressure.

Compressor Inlet

The following summarizes the three compressor inlet connections and the associated pitfalls:‪

  • Turbocharger: Must be consistent with pressure and speed limits determined by the manufacturer.
  • Inlet side of the turbocharger: Engine air cleaner must be serviced at regular intervals. (See manufacturer's instructions)
  • Local air filter: Local air filter must be serviced at regular intervals. (See manufacturer's instructions)

Inlet Connection Recommendations

Inlet connection recommendations are as follows:‪

  • Line size: The preferred inlet size is 19 mm (0.75 in.) I.D. The minimum line size for the inlet connection is 15.9 mm (0.625 in.) I.D., for either naturally aspirated or turbocharger applications.
  • Depression of inlet pressure: A compressor inlet connected to the engine induction system must not depress the intake pressure to more than 635 mm (25 in. H2 O).
  • Separate inlet filters: Separate inlet filters must not depress the intake pressure to more than 635 mm (25 in. H2 O). The polyurethane sponge strainer should be serviced every 8050 km (5000 miles) or 150 operating hours. The paper element type should be replaced every 32,190 km (20,000 miles) or 800 operating hours.

Alcohol Evaporator

The alcohol evaporator can be used to reduce the potential for an air system freeze-up; however, it does not remove any moisture from the air system, but only lowers its freezing point. The preferred method of protecting the air system against cold weather freeze-up is with an air dryer. The moisture generated by the compression of air is removed, thus minimizing the possibility of contaminating the air system.‪

Unloader Pressure

In a turbocharged application a minimum pressure of 5.9 bar (85 psi) is required to insure proper unloader operation. The cut in pressure of the governor used must be at least 6.6 bar (95 psi). ‪


Governor guidelines are as follows:‪

  • Governor/Reservoir line routing: The governor/reservoir line should slope downward toward the first reservoir to eliminate a potential water trap or ice restriction. The governor may operate erratically if the governor/reservoir line becomes restricted. Compressor unloader or inlet valve damage may result. The governor/reservoir line should be plumbed into the top of the reservoir. The governor/reservoir line should never be plumbed into the bottom of the reservoir, because water and contamination may cause the governor to malfunction.
  • Governor/reservoir line size: The governor/reservoir line size is 6.4 mm (0.25 in.) I.D. tubing; however, 4.8 mm (0.375 in.) I.D. is acceptable.
  • Governor mounting: The governor mounting is on the compressor unloader pad. The governor may be remote mounted; however, the line from the governor to the unloader pad should be as short as possible (not to exceed 1.2 m [4 ft.]). The governor should be mounted with the exhaust port toward the road surface, to reduce the possibility of moisture contamination.
  • Waterproof governor: In situations where the exhaust port of the governor must be pointed upward, a special waterproof governor should be used.
  • High temperature governor: A high temperature governor should be used when the under-hood ambient temperature exceeds 93°C (200°F).

Compressor Orientation

The maximum side-to-side roll is degrees beyond the nominally designated orientation. Some models are designed with an orientation other than zero degrees.‪

Power Angle

The maximum fore-aft tilt (power angle) the compressor may be subjected to is eight degrees for the TF550 and six degrees for the TF750. These values may be increased by five degrees if the compressor is turbocharged or if the flange-mounted compressor is bottom drained. ‪

Allied Signal® and Bendix® are registered trademarks of Allied Signal.‪

Series 60 Service Manual - 6SE483
Generated on 10-13-2008

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