Control valves
Control Valves are primary mechanical elements in a process creating a controllable flow of media. The controllable variation in flow are achieved by varying the size of the flow passage. The direct control of flow rate enables control of process parameters such as pressure, temperature, and liquid level.
Control Valves – how they work
The opening and closing of the valves are usually done by electrical, hydraulic or pneumatic actuators. The valve position is decided by an input signal, normally 4-20 mA where 4 mA corresponds to closed valve and 20 mA to fully open.
Any value between 4 to 20 mA is then corresponding to a mechanical position, degrees for rotary valves and lift in mm for linear valves. In most cases a positioner with an internal control loop are used i.e. the mechanical position is sensed continuously and compared to the input set value, giving the positioner the possibility to accurately set the angle of lift.
Some common types of Control Valves
There are many different mechanical solutions for controlling flow of liquids, gases, steam, slurries, powders, pellets and granulate. Common types of control valves are:
Ball Sector valves, Globe valves, Plug valves, Butterfly valves, Ball valves, Pinch valves, Diaphragm valves and many more…
Which valve will fit your application?
All the types of commercially available control valves are designed for its specific use e.g. media types, temperature range, pressure range and flow range. There are no valves that handles all applications – make sure to consult a specialist before deciding what type of control valve, actuator and positioner that will give the lowest overall life cycle cost.
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Globe style control valves
Globe style control valves are the most common type of control valve. They got their name because in the early design of the valve the interior cavity of the valve had a circular or globe shape. Globe valves are also known as Linear Valves because the stem that actuates the valve moves up and down in a straight line.
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Microflow globe valves
Microflow globe valves are small control valves designed for pilot plant and research applications. They are suitable for control of low flow applications in all types of process industries. Per definition in EN60534 microflow valves are valves with a Cv > 0,05.
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Ball sector valves
Ramén Ball Sector Valves are used as isolating and control valves for fluids, gases, turbid media and sludge, especially in the mining industry, pulp and paper industry and chemical industry. Abrasive slurries of iron ore, coal, lime and fly ash are also controlled with this type of valve.
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Eccentric rotary plug valves
Eccentric rotary plug valves use a cam like motion to move the plug into the seat thus effecting closure. There are several benefits to this style of valve. There is less torque on the plug once it breaks free of the seat as it is no longer in contact with the seat. Because there is no contact eccentric rotary plug valves will not exhibit the wear normally seen with a ball valve, whose plug is in constant contact with the seat throughout its travel.