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Chemical Process Technology

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Wednesday, September 24, 2008

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Control valve has been widely used in Chemical & Process Plant for material feeding control and operating condition control. Today control valve technology is high in reliability and availability and long life span. It is a very mature technology. There are many handbooks and articles presented in earlier post "Useful Documents Related to Control Valves" and they are available for download.

Recommended :
Besides theory and practical knowledge in articles, there are still many frequently asked questions related to control valve. Following is a list of frequently asked question (FAQ) related to control valve. It is pretty useful especially to young engineer.
The question includes :
  • What is CV ?
  • What is the difference between actual, standard and normal flow rates for gases ?
  • What is Cavitation ?
  • What is flashing ?
  • What is choked flow ?
  • How can cavitation damage be contained ?
  • How can flashing damage be contained ?
  • Is the velocity of a fluid in a control valve critical ?
  • What is the difference between a liquid, a vapour and a gas ?
  • What is a desuperheater and how does it differ from an attemporator ?
  • Why do different control valves have different characteristics ?
  • Definition of linear and equal percent characteristic ?
  • What is the difference between installed and inherent characteristics ?
  • Why are control valves sometimes very noisy ?
  • Can two control valves be used in series in high pressure drop applications ?
  • Can two control valves be used in parallel to handle high turndown applications ?
  • What is the difference between rangeability and turndown ?
  • What process data is required to size a control valve ?
  • What is incipient cavitation?
  • What is the difference between a diffuser plate and a choke ?
  • What is a field reversible actuator ?
  • Will separable flanged valves seal in a pipeline ?
  • What is the trim in a control valve ?
  • What is meant by Critical Pressure and Critical Temperature ?
  • Is flow through a control valve turbulent or laminar ?
  • What is vapour pressure ?
  • Specific Gravity is the ratio of the density of a liquid to the density of water – What is Specific Gravity of a Gas ?
  • What is meant by Cryogenic ?
  • What materials can be used for Oxygen Service ?
  • Why do Oxygen valves require degreasing ?
  • Are safety valves, regulators and isolating valves all examples of control valves ?
  • Why do some control valve actuators have a small internal fail action spring and some are external and larger ?
  • Why is live loading sometimes offered on valves ?
  • Why is reduced trim required in control valves ?
  • How is the characteristic determined in a globe valve ?
  • What effect does the positioner cam have on the valve characteristic ?
  • Why is Energy dissipation an important factor in control valve selection?
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posted by Webworm, 11:12 AM

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