TYPES OF VALVES
Pinch Valve Bodies
Pinch valves have molded bodies reinforced with fabric. Pinch valves generally have a
maximum operating temperature of 250oF. At 250oF, maximum operating pressure varies
generally from 100 psig for a 1-inch diameter valve and decreases to 15 psig for a 12-inch
diameter valve. Special pinch valves are available for temperature ranges of -100oF to 550oF
and operating pressures of 300 psig.
Most pinch valves are supplied with the sleeve (valve body) exposed. Another style fully
encloses the sleeve within a metallic body. This type controls flow either with the conventional
wheel and screw pinching device, hydraulically, or pneumatically with the pressure of the liquid
or gas within the metal case forcing the sleeve walls together to shut off flow.
Most exposed sleeve valves have limited vacuum application because of the tendency of the
sleeves to collapse when vacuum is applied. Some of the encased valves can be used on vacuum
service by applying a vacuum within the metal casing and thus preventing the collapse of the
Figure 19 Typical Butterfly Valve
A butterfly valve, illustrated in
Figure 19, is a rotary motion
valve that is used to stop,
regulate, and start fluid flow.
Butterfly valves are easily and
quickly operated because a 90o
rotation of the handle moves the
disk from a fully closed to fully
opened position. Larger butterfly
valves are actuated by handwheels
connected to the stem through
gears that provide mechanical
advantage at the expense of speed.
Butterfly valves possess many
advantages over gate, globe, plug,
and ball valves, especially for
large valve applications. Savings
in weight, space, and cost are the
most obvious advantages.
maintenance costs are usually low
because there are a minimal
number of moving parts and there
are no pockets to trap fluids.