A control valve is a valve used to control media flow by varying the size of the flow passage as directed by a signal from a controller. This enables the direct control of flow rate and the consequential control of process quantities such as pressure, temperature, and media level.
The opening or closing of automatic control valves is usually done by electrical, hydraulic or pneumatic actuators. Normally with a modulating valve, which can be set to any position between fully open and fully closed, valve positioners are used to ensure the valve attains the desired degree of opening.
Air-actuated valves are commonly used because of their simplicity, as they only require a compressed air supply, whereas electrically-operated valves require additional cabling and switch gear, and hydraulically-actuated valves required high pressure supply and return lines for the hydraulic fluid. The pneumatic control signals are traditionally based on a pressure range of 3-15psi or more commonly now, an electrical signal of 4-20mA for industry. Electrical control now often includes a "Smart" communication signal superimposed on the 4-20mA control current, such that the health and verification of the valve position can be signalled back to the controller.
An automatic control valve consists of three main parts in which each part exist in several types and designs:
Valve actuator - which moves the valve's modulating element, such as ball or butterfly.
Valve positioner - Which ensures the valve has reached the desired degree of opening. This overcomes the problems of friction and wear.
Valve body - in which the modulating element, a plug, globe, ball or butterfly, is contained
One of our strengths at Tyne Valves is our knowledge and capabilities surrounding actuation and control valves. We have the in-house capability of actuating and supplying actuated valves to the customer's direct specification whether the emphasis is on a general control basis or a more finer control requirement.
Please get in touch with a member of our team for price and availability.