SB-10057468-5509

Technical Bulletin
Bulletin No: TCH-008-044
Subject:

Effective Date: 1-9-2015

Cancels: N/A

Page: 1 of 2

Steps to Prevent Air Brake System Contamination – Best Practices

There are many myths and much misinformation when it comes to minimizing the impact of contamination
in the air braking system. Bendix Commercial Vehicle Systems LLC (Bendix) has found that the majority of
the procedures available today do not reflect current recommended practices for air treatment and storage
systems. Chief among our concerns are the concepts that air system antifreeze or alcohol is often considered
acceptable, along with the practice of draining air system reservoirs daily.
Refer to Bendix Technical Bulletin TCH-008-042 which strongly discourages the use of alcohol in the air
braking system.
Recommended Reservoir Draining & Dryer Service Intervals
Bendix discourages draining air system reservoirs daily when powered vehicles are equipped with a properly
functioning desiccant type air dryer. Why? Because daily draining tends to saturate an air system (with a
properly functioning air treatment system) on initial charge, and because it also causes the system’s air
compressor to work unnecessarily, thus reducing its durability.
Refer to the chart below for recommended reservoir draining and air dryer service intervals for powered
vehicles:
Air
Typical Vehicle
Axles
*Reservoir Drain Interval
*Desiccant
Usage
Vocation
(Whichever comes first)
Cartridge
Replacement
Hours
Mileage
Time
Standard

Line haul, city delivery

5 or less

900

25,000

3 months

Every 3 years

Medium

Double trailer trains, light
transit, light off-highway

8 or less

450

12,000

2 months

Every 2 years

High

Multiple trailer trains, city
transit, school bus, heavy
duty off-road

11 or less

300

6,000

1 month

Every year

* If more than just a trace of moisture is found in any of the reservoirs if may be necessary to replace the desiccant cartridge.

Completely draining reservoirs can reduce the life expectancy of all of the components in the air braking
system by flushing internal lubrication. Air dryers operate most efficiently when the reservoir pressures are
between governor cut-in and cut-out.
System Design Limitations
Total air system demand must be considered for proper sizing of the charging, treatment, and storage system
on a powered vehicle. It is very important to take into account the number of axles ­­— and all auxiliary features
for the entire vehicle combination ­­— as this will minimize the possibility of system freeze-up on combination
including any trailers. Air system leakage can cause contamination in the system by challenging the charging
and air treatment system capacity. Please refer to Bendix Application Guidelines BW2600 for air dryers
and BW2625 for air compressors. For acceptable air leakage recommendations refer to video BW2327.

Page: 2 of 2

TCH-008-044
Bulletin No:

Shutting Vehicle Down in Cold Temperatures
When powered vehicles must be shut down for a period of time and ambient temperatures are expected to
be below freezing, it is beneficial to fan the air brake system down to just below the system cut-in pressure.
Doing this with the engine OFF, while it is still at operating temperature, allows the compressor and dryer
to be in the “charge mode” on engine start-up. This minimizes the potential for these components to be
frozen in the “unloaded mode” until the air dryer heater and power train heat allows these units to reach
normal operating temperature.
Protecting Towing Connections on all Towing Vehicles
For all tractors, towing trucks, trailers and converter dollies, Bendix recommends that vehice
operators take precautions to ensure that all glad-hand connections are protected from the
environment when not coupled. This involves using glad-hand hangers and glad-hand dummy couplings
for both front (input on trailers & dollies) and rear (output on tractors, trailers, & dollies) couplings to protect
against the entry of foreign airborne contaminants. This includes protection from road debris, contaminants
and weather elements in the form of precipitation. These items can be sucked into the open glad-hands
due to the vortex created at the back of the trailer as it travels down the highway.
Please note that all front (input) glad-hands still need to be vented to atmosphere. This can be through a
small hole ­­— or breather valve ­­— to prevent mishaps such as “false parking” via trapped pressure in the
trailer service line, or to prevent the unintentional release of the trailer parking brakes by pressurizing the
trailer supply line as a result of system leakage. To further reduce any potential issues related to liquid water
entering via open glad-hand connections, Bendix offers the Cyclone DuraDrain® trailer water separator
which helps remove all liquid water and other contaminants from the trailer control and supply lines. See
SD-08-2402 for information on the Cyclone DuraDrain trailer water separator.
Also, note that Bendix recommends vented shut-off valves on the back of trailers and the use of the Bendix®
SV-4™ synchro valve in the supply line on converter dollies to prevent false charging on trailers and dollies.
Refer to technical bulletin TCH-003-027 for details concerning this recommendation.
Shown below are the documents referenced in this bulletin, as well as additional pieces that may be of
interest. To download or order these items and more, visit the document library online at www.bendix.com.

Technical Bulletins

Service Data

Miscellaneous

TCH-003-027

SD-08-187

SD-08-2412

BW2600

TCH-008-021

SD-08-187B

SD-08-2416

BW2625

TCH-008-022

SD-08-2401

SD-08-2417

BW2327

TCH-008-042

SD-08-2402

SD-08-2418

SD-08-2403

SD-08-2433

SD-08-2407

SD-98-9808

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