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
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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
