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