Page 14 - Valve Selection Handbook

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INTRODUCTION

Valves are the components in a fluid flow or pressure system that regu-
late either the flow or the pressure of the fluid. This duty may involve
stopping and starting flow, controlling flow rate, diverting flow, prevent-
ing back flow, controlling pressure, or relieving pressure.
These duties are performed by adjusting the position of the closure
member in the valve. This may be done either manually or automatically.
Manual operation also includes the operation of the valve by means of a
manually controlled power operator. The valves discussed here are man-
ually operated valves for stopping and starting flow, controlling flow
rate, and diverting flow; and automatically operated valves for prevent-
ing back flow and relieving pressure. The manually operated valves are
referred to as manual valves, while valves for the prevention of back
flow and the relief of pressure are referred to as check valves and pres-
sure relief valves, respectively.
Rupture discs are non-reclosing pressure-relieving devices which ful-
fill a duty similar to pressure relief valves.
Fundamentals

Sealing performance and flow characteristics are important aspects in
valve selection. An understanding of these aspects is helpful and often
essential in the selection of the correct valve. Chapter 2 deals with the
fundamentals of valve seals and flow through valves.

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