Answer / aftab ahmed mazari

These are flow paterns.
a. Equal percntage
b. Linear
c. Quick opening

The plug and cage is made in such a way that you can get
flow any one of above construction.
Suppose, Valve cage, plugs are Equal percentage, then at
opening of valve of 30 percent, you may get flow of only 6
to 8%
If linear, then flow also 30%,
If quick opening, then flow almost double, about 60%,
It all depends upon process requirements.
Suppose for vent valve, usually quick opening type valves
are used

aftabmazari@yahoo.com

Answer / imran

•Linear - flow capacity increases linearly with valve
travel.
•Equal percentage - flow capacity increases exponentially
with valve trim travel. Equal increments of valve travel
produce equal percentage changes in the existing Cv.
•A modified parabolic characteristic is approximately
midway between linear and equal-percentage characteristics.
It provides fine throttling at low flow capacity and
approximately linear characteristics at higher flow
capacity.
•Quick opening provides large changes in flow for very
small changes in lift. It usually has too high a valve gain
for use in modulating control. So it is limited to on-off
service, such as sequential operation in either batch or
semi-continuous processes.
•Hyperbolic
•Square Root

where we are used split range control

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