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The 3328 is a poppet-type normally open relay valve.
The diaphragm spring forces the valve stem down, which
keeps the poppet open. This allows air to flow from the
source of supply directly to the device actuated. When
air pressure enters pilot port number two, it will
over-come the diaphragm spring and close the valve.
In this position, the source of air supply is closed
and all the accumulated air pressure in the out-line
is vented to exhaust. A second pilot signal can be
used in pilot port number one. This will assist the
spring and overpower pilot signal number two, and
again open the source of supply to the device actuated.
This dual pilot arrangement lends itself extremely
well in complex inter-locking circuitry. Various
springs are available to give the proper operating
characteristics.
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