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:
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.