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 The
Model 780 Altitude Control Valve, One Way Flow is an
automatic control valve designed to control the high water level
in reservoirs and tanks without the need for external control
devices such as floats, etc.
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
three-way control principle, has pressure applied from or pressure
vented through the three-way altitude pilot.
 The
altitude pilot senses reservoir or tank pressure head. It closes
at a pre-set pressure head and opens on decreasing pressure
head.
The closing and opening of the pilot alternatively pressurizes
or vents the pressure in the upper control chamber causing the
main valve to close or open thus maintaining a constant pressure
head in the reservoir or tank.
When the head pressure falls below the pilot setting the pilot
opens, pressure in the upper control chamber decreases and the
main valve opens to refill the reservoir or tank. When the head
reaches the set point of the pilot the pilot closes, pressure
in the upper chamber increases and the main valve closes to
stop flow into the tank or reservoir. The altitude pilot has
an adjusting screw to preset the desired head pressure.
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Valve Line Up
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