BENDIX BW2789 manual Description, Operation see Figure, Removal

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SD-08-203

Bendix® DRO Unloader Valve

4

CONTROL

1

SUPPLY

21

DELIVERY

3

EXHAUST

FIGURE 1 - DRO UNLOADER VALVE

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

ATTACHES

TO THE

EXHAUST OF

THE DRO VALVE

FIGURE 2 - SILENCER

exhaust to atmosphere. Any air pressure created by the compressor during the unload operations flows 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 fittings.

2.Remove the mounting hardware that secures the DRO unloader valve to the frame rail or mounting surface.

1