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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.
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