Chapter 3: Manual Valves: Section 3.7.3 - Manual-Pinch-Valve Operation

Generally, pinch-valve operation is quite simple. Turning the hand-
wheel lowers the compressor and moves the upper wall of the liner
toward the static lower wall, which is supported by the bottom of the
casing or the bottom bracket. In throttling situations, the manual operator
is turned until the required flow is achieved and is then left in
that position. In on–off situations, the manual operator is turned until
the closure mechanism presses the upper wall of the liner against the
lower wall, which is supported by either a static lower bar or the bottom
of the casing. As more thrust is applied by the manual operator,
the two surfaces seal more tightly. When the pinch valve opens, the
turning action of the manual operator is reversed, raising the compressor
and allowing the liner to open as it moves toward its natural
relaxed position. As the opening increases, the pressure of the process
pushes the liner against the closure mechanism, which widens the
flow area more as the closure mechanism is raised. Eventually, at the
full-open position, the liner will have reached its full area capacity.

With pressure-assisted pinch valves, fluid pressure is introduced
above and below the body liner. When the introduced pressure is
greater than the pressure of the process fluid, the liner begins to collapse.
As the introduced pressure builds, the liner begins to collapse,
restricting the flow until the liner totally collapses and forms a seal
between the upper and lower walls. When the introduced pressure is
relieved or if the process pressure builds, the forces reverse and the
liner walls separate, opening the pinch valve.

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