Section 12 - Air Equipment - Group 12 Air Equipment - General Information M11 Page 12-3 The compressed air system normally consists of a gear driven air compressor, an air governor, air tanks and all necessary plumbing. The Holset single and two cylinder air compressors are engine-driven piston-type compressors which supply com- pressed air to operate air activated devices. The com- pressor runs continuously but has a loaded and unloaded operating mode. The operating mode is controlled by a pressure-activated governor and the compressor unloading assembly.
When the air system reaches a predetermined pressure, the governor applies an air signal to the air compressor unloader assembly causing the unloader valve to hold the compressor intake valve open and compressed air stops flowing into the air system. As the air in the air system is used, the pressure drops. At a predetermined pressure the governor exhausts the air signal to the compressor unloader assembly allowing the compressor to again pump compressed air into the air system. E-Type Air Compressor Air compressors built with the E-Type unloader can be identified by the letter ‘‘E’’ (SS296E), and by the caution on the dataplate.