A process control valve is a valve that is used to control various conditions in a process such as flow, level of liquid , pressure and temperature by either fully or partially opening or the vice versa. Control valves function once they receive signals from devices called controllers that compare a “standard point” to a “process variable”, whose value is made available by sensors that monitor any changes in the conditions.
Оpening or closing of the process control valves is commonly done automatically by use of pneumatic, hydraulic or electrical actuators. There are positioners that control actuators based on pneumatic or electric signals. These signals are typically based on the 3-15psi (0.2-1.0bar) but the more common today are 4-20mA signals for industry. Оther common protocols include 0-10V for a HVAC system, “Sart” systems, Profibus, Fieldbus Foundation and HART.
A process control valve basically comprises of three main parts; valve’s actuator, valve’s body and valve’s positioner. Each of the parts is available in different types and designs. The most common types of these valves are the sliding-stem globe valves and angle valves.