Idex Liquid Controls A8180 Series Installation-Parts page 8

Air Check and Differential Valves
Air check and differential valves are spring loaded
valves on the outlet side of the meter. Most Liquid
Controls meter systems with an air eliminator also
have an air check or a differential valve. Air
eliminators and air-check (or differential) valves work
in conjunction to stop the flow of product through the
meter until the air is eliminated from the system. In
order to do this, the air eliminator and the valve are
piped together at installation.
Air-check (or differential) valves are normally closed,
but when the pump starts and pushes product into
the system, the valve spring will give way to the flow
pressure. In order to keep the valve closed when air
is being expelled from the air eliminator, the air from
the air eliminator is routed through the piping to the
back side of the valve spring. The combined force of
the expelled air and the strength of the spring keep
the valve closed until the air is eliminated.
Limited Bleed Valve Plates
After the air is eliminated and the reed strips pull
away from the vent ports, the air pressure on the
back side of the spring is relieved and the valve
opens. To avoid the system shock sustained by an
abruptly opened valve, the pressure must be
released slowly. In order to do this, a 1/32-inch bleed
hole has been drilled into one of the valve plates so
that it sits over a bypass port. The small bleed hole
gradually releases the pressure on the valve spring
allowing it to open it slowly.
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Mechanical Air & Vapor Eliminators
8