Instruction Manual

ManualsBrandsBendix Commercial Vehicle Systems ManualsEquipmentDRO UNLOADER VALVE

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SD-08-203

Bendix

DRO Unloader Valve

FIGURE 1 - DRO UNLOADER VALVE

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

CONTROL

DELIVERY

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

Summary of content (4 pages)

PAGE 1
SD-08-203 ® Bendix® DRO Unloader Valve 4 CONTROL ATTACHES TO THE EXHAUST OF THE DRO VALVE 1 SUPPLY 21 DELIVERY 3 EXHAUST FIGURE 1 - DRO UNLOADER VALVE FIGURE 2 - SILENCER DESCRIPTION exhaust to atmosphere. Any air pressure created by the compressor during the unload operations flows out the DRO unloader valve to atmosphere. The Bendix® DRO unloader valve allows an air dryer with a turbo-cutoff valve to be used as a discharge line unloaded dryer.
PAGE 2
INSTALLATION The DRO valve can be installed in two configurations, series or parallel. Series Configuration The series configuration, shown in Figure 3, allows all the compressor discharge air to pass through the valve and into the dryer or reservoir.
PAGE 3
GENERAL SAFETY GUIDELINES WARNING! PLEASE READ AND FOLLOW THESE INSTRUCTIONS TO AVOID PERSONAL INJURY OR DEATH: When working on or around a vehicle, the following general precautions should be observed at all times. 1. 2. 3. 4. Park the vehicle on a level surface, apply the parking brakes, and always block the wheels. Always wear safety glasses. Stop the engine and remove ignition key when working under or around the vehicle.