BENDIX TCH-001-058 Dépliant
Technical
Bulletin
Bulletin No:
Effective Date:
Cancels:
Page: 1 of
Subject:
TCH-001-058
5-20-2010
N/A
2
Sound Emitted by Externally Unloaded Compressor
This bulletin identifi es a concern that can be mistakenly diagnosed as air system leakage.
Unloading air compressors externally, by means of allowing discharge air to be vented to atmosphere
rather than internally unloading the compressor, to stop the building of air system pressure is commonly
referred to as Discharge Line Unloading or DLU. In the unloaded mode DLU compressors provide a
continuous exhaust fl ow of air to atmosphere. This exhaust fl ow of air may be mistakenly diagnosed as
air system leakage. Although this fl ow of air is normal, the concern can be minimized by installing an
approved vent hose, or tube, to relocate or redirect the exhaust noise or by installing an approved silencer
at the exhaust outlet of the component relieving the pressure.
rather than internally unloading the compressor, to stop the building of air system pressure is commonly
referred to as Discharge Line Unloading or DLU. In the unloaded mode DLU compressors provide a
continuous exhaust fl ow of air to atmosphere. This exhaust fl ow of air may be mistakenly diagnosed as
air system leakage. Although this fl ow of air is normal, the concern can be minimized by installing an
approved vent hose, or tube, to relocate or redirect the exhaust noise or by installing an approved silencer
at the exhaust outlet of the component relieving the pressure.
Note that using a DLU purge valve in an air brake system that has a turbo charged air compressor inlet,
will result in loss of turbo pressure out of the dryer thereby, reducing engine power.
will result in loss of turbo pressure out of the dryer thereby, reducing engine power.
Bendix Commercial Vehicle Systems LLC is aware of two common means of externally unloading the air
compressor for air braked systems in use today, either through the air dryer or an external unloader valve.
compressor for air braked systems in use today, either through the air dryer or an external unloader valve.
The fi rst method is using an air dryer with a discharge line unloading (DLU) style purge valve assembly to
allow the compressor discharge air to be vented to atmosphere under the control of the normal air system
governor. The partial system sketch below illustrates the charging, treatment, and storage portion of an
air brake system utilizing the air dryer as the means of externally unloading the compressor. Note that
most Bendix
allow the compressor discharge air to be vented to atmosphere under the control of the normal air system
governor. The partial system sketch below illustrates the charging, treatment, and storage portion of an
air brake system utilizing the air dryer as the means of externally unloading the compressor. Note that
most Bendix
®
air dryers typically include a turbo cut-off purge valve design. To use the air dryer in the
manner illustrated, a DLU style purge valve is required.
Discharge Line Unloading with Air Dryer and DLU Style Purge Valve
Continued...
The Silencer Kit for use on AD-9
®
, AD-IP
®
, and AD-IS
®
air dryers is part number 5004224.
FRONT SERVICE
REAR SERVICE
AD-IP
®
AIR DRYER
WITH MUFFLER
SINGLE
CHECK
VALVE
SINGLE
CHECK
VALVE
D-2
®
GOVERNOR
D
S
UNL
RES
SUPPLY
COMPRESSOR
COMPRESSOR
DISCHARGE LINE