AIR BRAKE COMPRESSOR INLET CHECK VALVE (INFORMATION)

SUBJECT: AIR BRAKE COMPRESSOR INLET CHECK VALVE (INFO)

VEHICLES AFFECTED: 1990-91 5H, 6H, 7H MEDIUM DUTY TRUCKS WITH BENDIX BX 2150 COMPRESSOR

In above applications the BX-2150 Compressor is equipped with an inlet check valve and will continue to "pump" air out the open air dryer purge valve during the entire purge cycle. This action is not detrimental to either the compressor or air dryer and occurs only when a single cylinder compressor is equipped with an inlet check valve. This occurrence is the result of the inlet check valve taking over the function of the compressor inlet valve during the unloaded mode.

INLET CHECK VALVE

The inlet check valve is used to prevent inlet oil misting during the unloaded cycle. The inlet check valve is mounted directly at the inlet cavity of the compressor. It consists of three parts, the inlet gasket, the inlet check valve reed, and the inlet check valve, as shown in Figure 1. During the compression cycle, the inlet check valve road is drawn away from its seat uncovering three inlet holes which allows air to flow into the compressor inlet cavity. A machined stop in the cylinder head inlet cavity limits the travel of the inlet check valve reed. In the unloaded cycle, the inlet check valve reed rests on its seat covering the three inlet holes. Air from within the compressor is prevented from existing the inlet cavity.

The inlet check valve may only be used in conjunction with cylinder heads incorporating the machined inlet check valve stop in the inlet cavity. Inlet gasket, Bendix part number #243430, is required since its thickness contributes to the minimum reed travel required. Either side of the inlet check valve reed may be installed next to the gasket; however, the free end (tip) of the inlet check valve reed must coincide with the machined inlet cavity stop in the cylinder head. The inlet check valve seat must be installed so that the two "half moon" indentations are on the side facing the inlet check valve as illustrated in Figure 1.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.