BENDIX BW2789 Manuale Utente

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1

SUPPLY

The Bendix

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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.

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).

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