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What is turndown and rangeability?

FAQ

What is turndown and rangeability?

by  MortenA  Posted    (Edited  )
Turndown and rangeability is usually associated with control valves. The definition of these are (from Perry):

maximum controllable flow
Rangeability R=--------------------------------
minimum controllable flow

normal maximum flow
Turndown ratio T=-----------------------------------
minimum controllable flow

Generally valves are designed so that T=0.7*R where R is between 20 and 50.

This definition complies with the ISA standard.

Turndown is often used not only in connection with control valves but also as a more "global" parameter e.g. for whole plants.
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