PURPOSE OF USING CONTROL VALVES

 


INTRODUCTION:

Process plants are made up of hundreds, if not thousands, of control loops that collaborate to produce a saleable product. A control valves especially global standard valves are good at regulating the fluid flow by changing the position of the valve plug or disc, which is controlled by an actuator.

WHAT IS A CONTROL VALVE?

A control valve is a power-operated device used to regulate or manipulate the flow of fluids, such as gas, oil, water, and steam. It is a critical part of a control loop and is an example of a final control element. These control valves made in Europe is by far the most common final control element used in industry today.

A control valve installation according to a leading control valve suppliers consists of the following components: a valve body, actuator, positioner, and accessories. A bonnet assembly and trim parts are included in the body. Its design is capable of withstanding fluid static pressure and differential pressure, allowing fluid flow, providing pipe-connecting ends, and supporting seating surfaces and a valve closure member.

Actuators are pneumatic, hydraulic, or electrically powered devices that provide the force required opening and closing a valve. True actuator movement is monitored and controlled by positioners to maintain the desired set-point. Electro-pneumatic transducers, pressure regulators, handwheels, position indicators, and limit switches are examples of accessories.

The type of valve used will be determined by the pipe size, the overall pressure at which the system operates the flowing media, process conditions, and other factors. There is also a trade-off between the cost of the valve and the cost benefits of tighter control.

A control valve can be operated electrically, pneumatically, or hydraulically and has two separate components: the Valve and the Actuator.

 VALVE BODY:

As said by leading control valves suppliers, predominantly control valve bodies are of different types or styles depending on service conditions, piping layout, and desired application. The two classes of control valves are Linear Motion and Rotary Motion.

OPERATIONAL METHODOLOGY:

The actuator is the device connected to the valve through the valve stem that provides the force required to move the valve.

As we said earlier, the actuator can be controlled electrically, pneumatically, or hydraulically. The most common and the most reliable is the “Pneumatic Actuator”.

The control valve receives a signal from a controller such as a PLC or a DCS in order to operate. The controller compares the actual flow rate to the desired flow value called the setpoint. The controller will produce an output to move the valve to bring the flow rate to the setpoint value.

Because of how pneumatic actuators are built, a control valve will fail to a specific position when a loss of the control signal occurs.

  • As the supply air pressure is increased, the rubber diaphragm pushes against the spring and moves the valve stem down into the valve body.
  • As the supply air pressure is reduced, the spring will move the valve stem out of the body.

The position to which the control valve is moved if a loss of signal occurs is referred to as the fail-safe mode. The type of fail-safe mode depends on the application for which the control valve is used.

There are many types of valves including:

  • Butterfly valves– These valves are typically lower cost.
  • Globe valves– These valves provide very precise control.
  • Ball valves–  These offer high flow capacity and wide rangeability.
  • Gate valves– These are typically used for shutoff and isolation.

TAKEAWAYS:

  • Check valves (other than the stop-check valves) stop flow only in one (reverse) direction.
  • Only angle-globe valves can be used for a 90-degree change in direction of flow.
  • Multiport ball-and-plug valves are used for changing the direction of flow and mixing flows.
  • Stop check valves can be and are used as stop, block, or isolation valves, in addition to being used as a check valve.
  • Some designs of ball-and-plug valves (contact the valve manufacturer) are suitable for throttling service.

CONCLUSION:

A control valve regulates the rate of fluid flow as the position of the valve plug or disk is changed by an actuator. Control valves are used to maintain a process variable as close as possible to the desired set point.

Fevisa being a reputable European valve manufacturers and a leading Valve Stockist in Dubai are dedicated to helping customers select the control valve best suited for the existing service conditions.

Frequently several correct choices may be available, thus it is important for customers to provide the valve manufacturers with their proper industrial requirements to avail a better guidance in their control valve selection.

We at Fevisa using all the perks that manufacturer and valve suppliers offer ensure that our products will perform for the long haul and we properly known as valve stockist. Our team of designers & engineers can assist you into making the right choice of the kind of valve for your application. Fevisa is ever ready to help you out in the choice of stock valves.

Contact @ Fevisa for further queries.

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