Control Valves
Control valves are valves used to control conditions such as 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 variable" whose value is provided by sensors that monitor changes in such conditions.[1] Control Valve is also termed as the Final Control Element.
The opening or closing of control valves is usually done automatically by electrical, hydraulic or pneumatic actuators. Positioners are used to control the opening or closing of the actuator based on electric, or pneumatic signals. These control signals, traditionally based on 3-15psi (0.2-1.0bar), more common now are 4-20mA signals for industry, 0-10V for HVAC systems, and the introduction of "Smart" systems, HART, Fieldbus Foundation, and Profibus being the more common protocols. Some of the control valve available are Reverse Double-Ported Globe-Style Valve Body, Three-Way Valve with Balanced Valve Plug, Flanged Angle-Style Control Valve Body, Valve Body with Cage-Style Trim, Balanced Valve Plug, and Soft Seat.
A control valve consists of three main parts in which each part exist in several types and designs:
Valve's actuator
Valve's positioner
Valve's body
Types of control valve bodies
The most common and versatile types of control valves are sliding-stem globe and angle valves. Their popularity derives from rugged construction and the many options available that make them suitable for a variety of process applications, including severe service. Control valve bodies may be categorized as below:
Angle Valves
Cage-style valve bodies
DiskStack style valve bodies
Angle seat piston valves
Globe Valve
Single-port valve bodies
Balanced-plug cage-style valve bodies
High capacity, cage-guided valve bodies
Port-guided single-port valve bodies
Double-ported valve bodies
Three-way valve bodies
Diaphragm Valves
Rotary valves
Butterfly valve bodies
V-notch ball control valve bodies
Eccentric-disk control valve bodies
Eccentric-plug control valve bodies
Sliding cylinder valves
Directional control valve
Spool valve
Piston Valve
Air-operated valves
Air-operated valve
Relay valve
Air-operated pinch valve