BENDIX TCH-003-036 User Manual

Technical Bulletin

Bulletin No.: PRO-03-36 Effective Date: 2/1/93 Page: 1 of 2

Subject: Proper Use of Two Button Modular Dash Control Valves

Two button modular dash control valves are designed so that the control valves operate
in the following manner:

• When the yellow (system park) button is pulled out, the trailer supply valve
automatically “trips” and the red button “pops out”. This operation applies the
parking brakes of both the tractor and trailer and closes the “control” and
“supply” lines to the trailer. (See Fig. 1)

• The red (trailer air supply) button may be subsequently pushed in. This
operation releases the trailer parking brakes and supplies air to operate trailer
auxiliary devices. (See Fig. 2)

• Pushing in both the yellow and red buttons releases both the tractor and
trailer parking brakes and opens the trailer “control” and “supply” lines. (See
Fig. 3)

It has come to our attention that some vehicle operators are using dash control valves
improperly when parking combination vehicles, overriding the automatic function of the
system by holding the red button in when pulling the yellow button. Bendix does not
recommend parking combination vehicles in this manner, since this parks the tractor but
does not park the trailer. Fig. 4 DEPICTS THE IMPROPER USE OF THE DASH
CONTROL VALVE.

There may, however, be situations where it is desirable to release the trailer parking
brakes while the tractor remains parked, by depressing the red button. This procedure is
generally used with the vehicle attended, to enable the use of auxiliary devices on the
trailer, i.e. pump-off.

Bendix has determined that if vehicles fitted with its MV-3 dash control valve are
operated in a manner where the red button is not allowed to “pop out” automatically and
the valve remains inoperative for extended periods, under pressure, this may impact its
ability to function automatically during parking brake applications.

It is recommended that when parking, both yellow and red buttons should be in the
outward position and whenever possible the engine should be off, with the vehicle in
gear and the front wheels turned toward the curb. This procedure will ensure safe
parking and proper operation of the dash control valves.