F-1031, Section 2119
Page 24 of 24
Shuttle Valve Function
The shuttle valve is part of the control air circuit and really
only comes into play during a compressor shutdown. Its
primary function is to provide a means (pathway) of reliev-
ing compressor air (pressure) and not allowing compres-
sor oil to escape at the same time
Using the two figures below, let’s go through how the shut-
tle valve works.
The figure on the left shows the shuttle valve in a closed
position. This occurs when the compressor inlet air pres-
sure (CIAP) is less than the compressor discharge air
pressure (CDAP).
When the compressor is running, the CIAP is always 14.5
psia or less and the CDAP is 40 psig or greater (minimum
pressure valve setting), allowing the shuttle valve to stay
closed.
The figure on the right shows the shuttle valve in an open
position. This occurs when the CIAP is equal or greater
than the CDAP pressure (note the slightly larger piston
surface on the CIAP side than the CDAP).
When the compressor shuts down and the rotors stop
turning, the CIAP and CDAP equalize allowing the shuttle
valve to open. With the shuttle valve open, air stored in
the compressor/sump tank is allowed to escape from the
air discharge through the shuttle valve and onto the air
bleed off outlet where it is exhausted.
Shuttle Valve - Open
Shuttle Valve - Closed
To Air
Bleed Off
Outlet
14.5 PSIA or Less
from Air Inlet
40 PSIG or Greater
from Compressor
Discharge
