Page 58 - Valve Selection Handbook

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MANUAL VALVES

FUNCTIONS OF MANUAL VALVES

Manual valves serve three major functions in fluid-handling systems:
stopping and starting flow, controlling flow rate, and diverting flow.
Valves for stopping and starting flow are frequently employed also for
controlling flow rate, and vice versa, while valves for diverting flow are
designed for that single purpose.

GROUPING OF VALVES BY METHOD
OF FLOW REGULATION

Manual valves may be grouped according to the way the closure mem-
ber moves onto the seat. Four groups of valves are thereby distinguishable:

1. Closing-down valves. A stopper-like closure member is moved to
and from the seat in the direction of the seat axis.
2. Slide valves. A gate-like closure member is moved across the flow
passage.
3. Rotary valves. A plug or disc-like closure member is rotated within
the flow passage, around an axis normal to the flow stream.
4. Flex-body valves. The closure member flexes the valve body.

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