to maintain loop performance levels. Improved process control accuracy that reduces process variability. Types of control valve Control valves are classified by attributes and features. Based on the pressure drop profile High recovery valve: These valves typically regain most of static pressure drop from the inlet to vena contracta at the outlet. They are characterised by a lower recovery coefficient. Examples: butterfly valve, ball valve, plug valve, gate valve Low recovery valve: These valves typically regain little of the static pressure drop from the inlet to vena contracta at the outlet. They are characterised by a higher recovery coefficient. Examples: globe valve, angle valve Based on the movement profile of the controlling element Sliding stem: The valve stem / plug moves in a linear, or straight line motion. Examples: Globe valve, angle valve, wedge type gate valve Rotary valve: The valve disc rotates. Examples: Butterfly valve, ball valve Based on the functionality Control valve: Controls flow parameters proportional to an input signal received from the central control system. Examples: Globe valve, angle valve, ball valve Shut-off / On-off valve: These valves are either completely open or closed. Examples: Gate valve, ball valve, globe valve, angle valve, pinch valve, diaphragm valve Check valve: Allows flow only in a single direction Steam conditioning valve: Regulates the pressure and temperature of inlet media to required parameters at outlet. Examples: Turbine bypass valve, process steam letdown station Spring-loaded safety valve: Closed by the force of a spring, which retracts to open when the inlet pressure is equal to the spring force Based on the actuating medium Manual valve: Actuated by hand wheel Pneumatic valve: Actuated using a compressible medium like air, hydrocarbon, or nitrogen, with a spring diaphragm, piston cylinder or piston-spring type actuator Hydraulic valve: Actuated by a non-compressible medium such as water or oil Electric valve: Actuated by an electric motor A wide variety of valve types and control operation exist. However, there are two main forms of action, the sliding stem and the rotary. The most common and versatile types of control valves are sliding-stem globe, V-notch ball, butterfly and angle types. Their popularity derives from rugged construction and the many options available that make them suitable for a variety of process applications. Control valve bodies may be categorized as below: List of common types of control valve Sliding stem Rotary Other See also References External links Process Instrumentation (Lecture 8):