Control valves
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Control valves are valves used to control conditions such as flow, pressure, temperature, and liquid level by fully or partially opening or closing in response to signals received from controllers that compare a "setpoint" to a "process variable" whose value is provided by sensors that monitor changes in such conditions.[1]
The opening or closing of control valves is done by means of electrical, hydraulic or pneumatic systems. Positoners are used to control the opening or closing of the actuator based on Electric, or Pnuematic Signals. These control signals, traditionally based on 3-15psi (0.2-1.0bar), more common now are 4-20mA signals for industry, 0-10V for HVAC systems, & the introduction of "Smart" systems, HART, Fieldbus Foundation, & Profibus being the more common protocols.
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[edit] Types of control valve bodies
The most common and versatile types of control valves are sliding-stem globe and angle valves. Their popularity derives from rugged construction and the many options available that make them suitable for a variety of process applications, including severe service.[2] Control valve bodies may be categorized as below:[3]
- Angle valves
- Cage-style valve bodies
- DiskStack style valve bodies
- Angle seat piston valves
- Globe valves
- Single-port valve bodies
- Balanced-plug cage-style valve bodies
- High capacity, cage-guided valve bodies
- Port-guided single-port valve bodies
- Double-ported valve bodies
- Three-way valve bodies
- Rotary valves
- Butterfly valve bodies
- V-notch ball control valve bodies
- Eccentric-disk control valve bodies
- Eccentric-plug control valve bodies
[edit] See also
- Control engineering
- Control system
- Instrumentation
- Instrumentation engineering
- Pneumatic flow control
- Process control
- HART Protocol
- Fieldbus Foundation
- PROFIBUS
[edit] References
- ^ Bela G. Liptak (Editor) (2003). Instrument Engineers' Handbook (4th Edition ed.). CRC Press. ISBN 0-8493-1083-0.
- ^ Hagen, S. (2003) "Control valve technology" Plant Services
- ^ Fisher Controls International Emerson Process Management website.
[edit] External links
- Control valve tutorials Tutorials covering the sizing, capacity and characteristics of control valves. Actuators, positioners, controllers and sensors are also discussed - Spirax Sarco
- Control Valve Handbook (4th Edition) A 297-page online book.
- Process Instrumentation (Lecture 8): Control valves Article from a University of South Australia website.
- CARRARO control valve
- Control Components Inc Website for severe service control valve.
- Valve Animations Flash animations demonstrating conventional and pressure independent control valve operation.
- [1] Masoleilan.com
- Samson AG Demo Valve Sizing Software. Basic Trial valve sizing programme.
- CONVAL - the PC software for engineers, planners and operators of industrial plants.
