Control valve basics: types, applications, and parts


What is a control valve?

A control valve, sometimes referred to as the Final Control Element is a valve used to control fluid or gas flow by varying the size of the flow passage as directed by a signal from a controller. This enables the direct control of flow rate and the consequential control of process quantities such as pressure, temperature, flow rate, and liquid level.

The opening or closing of automatic control valves is usually done by pneumatic, electrical, or hydraulic actuators. Normally with a modulating valve, which can be set to any position between fully open and fully closed, valve positioners are used to ensure the valve attains the desired degree of opening.

An automatic control valve consists of three main parts in which each part exists in several types and designs:

  • Valve Body subassembly – in which the fluid pressure in contained, as well as the modulating element, such as a plug, globe, ball, or disc.
  • Valve Actuator – which moves the valve's modulating element, such as plug, ball or disc.
  • Valve Positioner – which ensures the valve has reached the desired degree of opening. This overcomes the problems of friction and wear.

What are the main parts of a control valve?

Here is a look at our GFLO Globe Control Valve.

  • Valve Body: facilitates the passage of flow through the valve and is designed to contain the process at the given pressure, temperature and fluid composition.
  • Plug and Seat: The plug and seat modulate the flow through the valve. These are vital components within the valve trim and may be susceptible to wear and tear from either pressure drop through the valve as part of the process passing through the valve or contact with abrasive or corrosive mediums.
  • Seat Retainer: Clamps the seat ring in place and ensures correct compression of the lower seat gasket.
  • Bonnet: Forms part of the stuffing box assembly housing the valve packing. The valve packing prevents leakage from the stuffing box while allowing the stem to move up and down as needed to open and close the valve.  
  • Spring: The spring facilitates the valve fail action.
  • Control Valve Actuator: The control valve actuator acts upon a pneumatic signal from a valve positioner, or another pneumatic controller and adjusts the valve position accordingly. The MASCOT actuator can be disassembled and inverted to convert the valve from fail-closed to fail open or vice versa.

What are the main types of control valves?

  • GFLO Globe Control Valve
  • VFLO V-Ball Control Valve
  • DISKFLO High Performance Butterfly Valve
  • EFLO Eccentric Plug Control Valve

What are the main applications of control valves?

  • Oil & Gas
  • Industrial Gas Transmission
  • Power Generation
  • Chemical, Petro-Chemical & Refining
  • LNG Processing & Re-gasification
  • Industrial Gas
  • Steam / Desuperheating
  • Custom Design
  • Cryogenic Application
  • Compressor recycle and anti-surge applications
  • High Pressure acid leaching applications
  • FPSO & floating facility applications
  • Mineral processing applications

Why should you choose a MASCOT control valve?

The GFLO globe style control valve offers superior performance in liquid and gaseous services, while permitting easy, fast, and inexpensive maintenance. Unlike diaphragm-operated control valves, the spring cylinder-actuated GFLO provides stiffness and maintains high positioning accuracy, repeatability, controlled high speed and faithful response. And since it handles up to 150psig / 10.3 Barg supply air, it also has the thrust to shut off against much higher fluid pressures.

Most diaphragm actuators rely entirely on springs to close the valve. But the design of the MASCOT GFLO is such that the spring, the supply air pressure, and the fluid pressure itself combine to produce exceptionally tight shutoff. A self-aligning seat ring further enhances the shutoff capability of the GFLO globe control valve.

What are same common issues with control valves?

Some common issues with globe control valves include:

  • Leakage between the plug and seat,
  • Sticking valve, caused by galling within the trim area

Many common maintenance problems with globe valves can be traced to cage-guiding. The close metal-to-metal contact between the cage and plug often result in galling and sticking. MASCOT GFLO having double-top stem guiding completely avoids contact between the plug and seat retainer hence never suffers from the ills of galling & sticking.

The clamped-in seat and top entry trim permits easy, quick maintenance. Plus, with GFLO's high degree of parts interchangeability, fewer inventory parts are needed. The actuator is also lighter, smaller, and easier to handle than comparable diaphragm actuators.

How to choose the right control valve?

With MASCOT's Customer first approach, our standard GFLO's can be delivered within customer lead-time requirements, rather than what other manufacturers normally offer. MASCOT's GFLO is the simple, reliable, tough globe valve.

Do you need help deciding what type and size of valve you need? Try out our valve Sizing Software or get in touch with us for a quote.

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