Control valves are valves are used to control conditions of 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 variables”. The values for these parameters are provided by sensors that monitor changes in such conditions.Control valve opening or closing is usually done automatically by electrical, hydraulic or pneumatic actuators. Positioners are used to control the opening or closing of the electrical or pneumatic signals. These control signals normally based on 3-15psi (0.2-1.0bar), more common now are 4-20mA signals for industry, 0-10V for HVAC systems, and with the help of “Smart” systems, HART, Fieldbus Foundation, and Profibus being the more common protocols.
The most common types of control valves are sliding-stem globe and angle valves. Their popularity comes from rugged construction and the options available that make them suitable for severe services. In addition to the Globe design the Rotary Valves and Ball valves’ design are very commonly used in Oil & Gas and Petrochemical Industries.