One of the most common control element in the process control industry is the  Control Valve. A control valve helps regulate the flow of a fluid (gas, steam, water, or chemical substance) in order to keep the regulated process variables (pressure and flowrate) as close as possible to the desirable set point. Control valves can generally be designed to handle all types of fluids at temperatures from the cryogenic range up to 500+ degrees Celsius steam temperatures.

Control  Valves are typically operated with instrument air and are therefore characterised as pneumatically actuated valves. Electric and electro-hydraulic actuators can also be used with control valves. However, they are generally more complicated and thus more expensive compared with pneumatic actuators. They offer advantages where no instrument air or instrument gas supply source is available, in low ambient temperatures in which condensed water in pneumatic supply lines could freeze, or where unusually large driving (stem) forces are necessary for valve movement.

2012-04-09

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