Bendix Commercial Vehicle Systems DRO UNLOADER VALVE - Manual

1
®
SD-08-203
Bendix ® DRO Unloader Valve
FIGURE 1 - DRO UNLOADER VALVE
1
SUPPLY
DESCRIPTION
The Bendix ® DRO unloader valve allows an air dryer
with a turbo-cutoff valve to be used as a discharge line
unloaded dryer. The DRO valve allows discharge air
from the compressor to be exhausted to the atmosphere
in the unloaded mode of operation. Some compressors
are designed for discharge line unloading instead of head
unloading. When the DRO
valve is placed in the discharge
line it allows both the compressor and the dryer, with turbo-
cutoff, to function properly. The DRO
valve can be used to
convert a head unloaded compressor to a discharge line
unloaded compressor.
OPERATION (SEE FIGURE 1)
The DRO unloader valve discharges air in the compressor
discharge line to the atmosphere. During the charging
operation of the compressor, air travels into the supply port
(1) of the DRO valve. When the air brake system reaches
the cut-out pressure, a pneumatic signal from the governor
is sent to the control port (4) of DRO
unloader valve. The
pneumatic signal opens the DRO valve exhaust port (3)
allowing air pressure in the compressor discharge line to
4
CONTROL
21
DELIVERY
3
EXHAUST
exhaust to atmosphere. Any air pressure created by the
compressor during the unload operations fl ows out the
DRO unloader valve to atmosphere.
The exhaust (3) can be directed away from the valve using
a 3/4” rubber hose. The hose should be securely fastened
to the frame and should not run uphill or contain any kinks
or sharp bends.
An optional silencer, as shown in Figure 2, is available
to reduce noise level during the unloaded operation. The
silencer snaps into the bottom of the exhaust port (3).
REMOVAL
1. Disconnect the supply and delivery line fi ttings.
2. Remove the mounting hardware that secures the
DRO unloader valve to the frame rail or mounting
surface.
ATTACHES
TO THE
EXHAUST OF
THE DRO VALVE
FIGURE 2 - SILENCER