Control Valve And Its Functioning

ByAir-Mite

A control valve is a valve that is used to control fluid flow by varying the size of the flow passage in response to a control signal. This allows for direct control of flow rate as well as indirect control of process quantities such as pressure, temperature, and liquid level.

A control valve in Illinois is referred to as a “final control element” in automatic control terminology. It is an example of a final control element and is an important part of a control loop. By far the most common final control element used in industry today is the control valve.

How does a control valve operate?

Automatic control valves are typically opened and closed by electrical, hydraulic, or pneumatic actuators. Normally, valve positioners are used to ensure that a modulating valve, which can be set to any position between fully open and fully closed, achieves the desired degree of opening.

Since they only require a compressed air supply, air-actuated valves are commonly used, whereas electrically-operated valves require additional cabling and switchgear, and hydraulically-actuated valves require a high-pressure supply and return lines for the hydraulic fluid.

Pneumatic control signals have traditionally been based on a pressure range of 3-15psi (0.2-1.0 bar), or, more recently, an electrical signal of 4-20mA for industry or 0-10V for HVAC systems. Electrical control now frequently includes a “Smart” communication signal superimposed on the 4-20mA control current, allowing the valve position and health to be signalled back to the controller.

An automatic control valve is made up of three main parts, each of which comes in a variety of styles and designs:

    • The valve actuator: Moves the valve’s modulating elements, such as a ball or butterfly.
    • Valve positioner: This device ensures that the valve has opened to the desired degree. This eliminates friction and wears issues.
    • The valve body: Contains the modulating element, which can be a plug, globe, ball or butterfly.

Types of Control Valve

    • Globe Valve

Globe valves get their name from the globular cavity that surrounds the valve seat. A globe valve’s closure member is a plug with a flat or convex bottom that is lowered onto a matching horizontal seat in the valve’s centre. Raising the plug allows fluid to flow through the valve.

    • Gate Valve

A gate valve’s closure member is a flat face, vertical disc, or gate that slides down through the valve to block the flow. Gate valves are only found in flow shut-off applications because they are designed to operate in either the fully open or fully closed position. When fully opened, the disc is completely removed from the flow stream. When the valve is fully open, there is virtually no resistance to flow, so gate valves operate with a little pressure drop across the valve.

    • Diaphragm Valve

A diaphragm valve’s closure member is a deformed flexible surface (the diaphragm). The main advantage of a diaphragm valve is that it does not require a stem seal. Diaphragm valves are mostly used for shutting down slurries, corrosive or viscous fluids, but they can also be used for flow throttling.

    • Pinch Valve

A pinch valve is similar to a diaphragm valve; however, the entire valve body is flexible in a pinch valve, and the closure member pinches the valve shut, closing off the flow.

    • Ball Valve

A ball valve’s closure member is shaped like a ball and has a port for fluid flow. In the open position, a ball valve allows straight-through flow and shuts off flow when the ball is rotated 90 degrees. Ball valves are commonly used in flow shut-off applications due to their quarter-turn actuation and low-pressure drop.

    • Butterfly Valve

A butterfly valve’s closure member is a circular disc or vane with its pivot axis perpendicular to the direction of flow in the pipe. A butterfly valve, like a ball valve, allows straight-through flow when open and shuts off flow when the ball is rotated 90 degrees.

    • Plug Valve

A plug valve’s closure member is a cylindrical or tapered cylindrical shaped plug with a flow port. A plug valve, like a ball valve, allows straight-through flow when open and shuts off flow when the ball is rotated 90 degrees.

James Brown is the author of this article. For further detail about Mini Valve in Illinois. Please visit the website: airmite.com