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 The
Model 770 Rate of Flow Control Valve is an automatic
control valve designed to maintain a constant pre-set rate of
flow regardless of changing system pressures and demand.
It is a pilot controlled, hydraulically operated, diaphragm
actuated globe valve in either the oblique (Y) or angle pattern
design. Valve differential pressure powers the diaphragm actuator
open or closed.
The lower control chamber is connected through a fixed orifice
to the downstream pressure, which serves to cushion the closing
of the valve.
The upper control chamber, which operates on a two-way control
principle, has varying pressure produced by the rate of flow
pilot and the pilot's internal upstream restriction needle valve.
 The
rate of flow pilot senses the pressure differential across an
orifice plate or a "pitot" tube and modulates open or closed.
When the rate of flow increases the differential pressure across
the orifice plate or pitot tube also increases.
Sensing this increased differential pressure the pilot closes
and pressure in the upper control chamber increases. The main
valve modulates closed which decreases the rate of flow and
the pressure differential thus maintaining pilot setting.
Should the rate of flow decrease the differential pressure will
drop and the pilot will open causing pressure in the upper chamber
to decrease. The main valve will then open to increase the rate
of flow and the pressure differential and pilot setting will
be maintained. The rate of flow pilot has an adjusting screw
to preset the desired rate of flow and an internal needle valve
to control the closing speed.
Back to 700 Series Control
Valve Line Up
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