BENDIX TCH-001-010 User Manual

Technical Bulletin

Bulletin No.: PRO-01-10 Effective Date: 4/4/78 Cancels: NA Page: 1 of 2

Subject: D-2 Governor With Competitive Drain Valves

Some OEM manufacturers are triggering or piloting Expello Automatic Drain Valves from
the D-2 governor unloader line (see Fig. 1). Under certain operating conditions, the
drain device will start to function, thus lowering the supply reservoir pressure before the
D-2 governor reaches a definite trip point or a delivered pressure great enough to unload
the compressor. Consequently, the compressor does not unload, and if a Bendix HVSG
air dryer is installed, it will not cycle. Thus, it will not purge and the desiccant will
become saturated and will deteriorate.

In addition, it has come to our attention that in some cases, as a “fix” for this problem,
the lubricant is being washed out of the D-2 governor and replaced by oil. While this
may temporarily mask the problem, it will not correct it; and the oil can cause governor
failure.

As a result, Bendix HVSG finds it necessary to recommend that the Expello Automatic
Drain Valve not be directly operated by the D-2 governor unloader line. If an Expello
valve is to be used, it must be isolated from the D-2 governor. A two-way, pressure
hold-off valve in the unloader line, between the D-2 governor and the Expello Automatic
Drain Valve, will serve this function. A Bendix HVSG SV-1 valve piped with common
control and supply pressure from the governor unloader and delivering air to the Expello
valve will work (See Fig. 2).

Because failure to comply with the above recommendations constitutes improper
installation and/or application of HVSG devices, voiding of the HVSG warranty on
compressors, governors and air dryer may result.