Reference Manual

NORTH AMERICA
Emerson Process Management
Marshalltown, Iowa 50158 USA
T 1 [phone]
F 1 [phone]
www.EmersonProcess.com/Fisher
ASIA PACIFIC
Emerson Process Management
Singapore 128461 Singapore
T +(65) 6777 8211
F +(65) 6777 0947
www.EmersonProcess.com/Fisher
LATIN AMERICA
Emerson Process Management
Sorocaba 18087 Brazil
T +(55)(15)3238-3788
F +(55)(15)3228-3300
www.EmersonProcess.com/Fisher
EUROPE
Emerson Process Management
Chatham, Kent ME4 4QZ UK
T [phone]
F [phone]
www.EmersonProcess.com/Fisher
MIDDLE EAST & AFRICA
Emerson FZE
Dubai, United Arab Emirates
T [phone]
F [phone]
www.EmersonProcess.com/Fisher
inherent flow characteristic that is linear. With an inherent linear
characteristic, valves commonly have a narrow travel band over which
they exhibit an optimum installed process gain. Typically, this range is
30 to 50 percent of total travel. This band is called the control range.
Outside the ideal range, process gains become very high or very low,
and high process variability results.
Installed process gains were greater than 4 (the EnTech desirable
range is 0.5 to 2). Process variability in the loops were 3.5% and 8%.
The vacuum loop was manually adjusted. The valves displayed
excessive backlash, as illustrated in the graph.
Piping space is too limited to allow changing to segmented ball
valves. Swaging down to a smaller valve size would be very expensive
and time consuming.
SOLUTION
Fisher
®
Control-Disk
™
valves replaced the two troublesome valves,
and operators left the loops in manual to observe the valves’ behavior.
Then, operators put loops in automatic and saw good control
immediately. One valve was operating at 30% open, the other at 60%
open.
Variability was significantly reduced: from 8.0% to 3.0% in one loop
and from 3.5% to 1.6% in the other. Variability was further reduced
after the loops were tuned.
Vacuum control loops that were once troublesome were now not an
issue.
POWER GENERATIONPULP & PAPER
Tracking of valve input signal
and valve output (vacuum)
before and after installation of
Control-Disk
™
valves shows
dramatic reduction in process
variability.
© Fisher Controls International LLC 2008 All Rights Reserved.
Fisher and Control-Disk are marks owned by one of the companies in the Emerson Process Management business division of Emerson Electric Co. The Emerson
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The contents of this publication are presented for informational purposes only, and while every effort has been made to ensure their accuracy they are not
to be construed as warranties or guarantees, express or implied, regarding the products or services described herein or their use or applicability. All sales
are governed by our terms and conditions, which are available upon request. We reserve the right to modify or improve the designs or specifications of
such products at any time without notice. Fisher does not assume responsibility for the selection, use or maintenance of any product. Responsibility for
proper selection, use and maintenance of any Fisher product remains solely with the purchaser.
D351618X012 / H: /July 2008