ISM, ISMe, and QSM11 - 012-999 Compressed Air System - Overview

Air Compressor Air Inlet Line

In the 2002 ISM engine, the air compressor receives turbocharged air from the charged air supply before it mixes with the exhaust gas. Since no exhaust gas will be drawn into the air compressor, Original Equipment Manufacturers (OEMs) are able to utilize the same style air compressor and the air tank setup as with the previous ISM engine. This is a two piece line with a hose connection at the rear of the engine.

The compressed air system normally consists of a gear-driven air compressor, an air governor, air tanks and all necessary plumbing.

The Holset® and Cummins® single and two cylinder air compressors are engine-driven, piston-type compressors which supply compressed air to operate air activated devices. The compressor runs continuously, but has a loaded and unloaded operating mode.

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E-Type Air Compressor:

Holset® SS and ST model air compressors built with the E-Type unloader can be identified by the letter “E” (SS296E, SS338E, ST676E, and ST773E), and by the caution on the data plate.

All QE (QE296 and QE338) model air compressors are equipped with the E-Type unloader.

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E-Type System With Air Dryer:

Vehicles equipped with air dryers vented to the atmosphere during unloaded compressor operation, using the Holset® E-Type air compressor, require the installation of an econ valve to prevent excessive oil consumption.

NOTE: Some air dryers can have a built-in econ valve. Check with the manufacturer as to which type is installed.

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E-Type System Without Air Dryer:

Air systems without air dryers, or with air dryers not vented to the atmosphere during unloaded compressor operation, can use the Holset® E-Type unloader valve without modifying the air system.