Guide: How to Select and Size Process Flow Control Valves

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Knowing how to size and select flow control valves affects the ability to control any industrial process. Beyond that, knowledge of proper industrial valve sizing and selection also has a major impact on the overall cost of a project.

Carotek&#;s Valves Selection Guide gives a framework for process valve sizing and selection.  When you need more help with your final selection, please contact us.

Types of Industrial Valves

A range of flow control valves and valve automation products are specialized for industrial applications. The right type of valve for your application depends on flow control, function, and valve operation.

• Actuators are typically pneumatic to open and close the valve by operating the stem, and they can also be either manual or electric.
• Ball Valves feature tight shut-off and low pressure drop when open and are good for both on/off and throttling applications.
• Butterfly Valves, which are suitable for regulating flow, are generally used for low line pressure and large pipeline diameters.
• Check Valves are used to prevent back-flow.
• Knife Gate Valves are used for on/off service and for media such as slurries and/or abrasives
• Plug Valves, generally used for regulating flow, allow quick opening and tight shut-off.  Some with characterized plugs are suited for flow control.
• Sanitary & Hygienic Valves are used when the media is a food, beverage, or pharmaceutical product.
• Solenoid Valves are opened and closed automatically via an electrical/current signal.

These industrial valves may be either manual or automated and are an integral part of critical solutions for industrial, commercial, and municipal processes.

Sizing Process Valves

A key component of process valve sizing and selection is determining the right size valve for your application. Finding the right valve configuration enhances performance and lengthens service life.

The first step is to determine the flow through the diameter of the valve. In other words, find the appropriate flow coefficient (Cv) for the valve and the application. It&#;s important to use accurate information when evaluating your performance needs.

• For applications that require a check valve or an on/off, block, or isolating valve, usually the valve can be sized to existing hose, tube, or pipe sizes, unless there are other requirements.

• Sizing a flow control valve is more complicated because the flow constriction varies. For example, if you use only the maximum flow rate to select a valve, it could result in selecting an &#;oversized&#; valve. It&#;s important to factor in minimum, maximum, and normal flow rates and use the range of flow rates required.

Knowing how to size a valve is critical for both process and economic efficiency. Giving in to the temptation to select oversized control valves leads to poor process control and a reduction in service life.

Main Criteria for Selecting an Industrial Valve

You can choose the right type of valve for the application by using the media type, the materials of construction, the valve characteristics, the pressure/temperature of the media, and the pressure class of the piping system. Keep these criteria in mind when specifying any industrial valve:

1. Media Type &#; Whether liquid, gas, steam, or slurry, the right valve will depend on the characteristics of the media. The proper valve depends on the media&#;s concentration, specific gravity, viscosity, and material compatibility. Material compatibility may be limited when the media is toxic or corrosive, contains particulates, or has a high coefficient of expansion.
2. Temperature &#; Both operating temperature and ambient temperature affect valve selection, and fluid temperature range also affects specific gravity and viscosity.
3. Pressure &#; Pressure requirements include operating range, maximum, and finally whether a valve for minimal differential pressure might be needed.
4. Flow &#; Flow characteristics that affect valve selection include rates for normal, minimum, and maximum

You also need to consider the valve function, actuation method, valve automation, and ongoing maintenance requirements of the valve, and whether you&#;re specifying metric or imperial units.

Valve Configuration

Once you have completed process valve sizing and selection, it&#;s time to configure the valve assembly. This may include selecting the (pneumatic or electric) actuator and/or valve positioner. When a positioner is used, you&#;ll need to determine the control signal and other accessories required (limit switches, solenoid valves). Actuators must be sized to actuate the valve. When selecting pneumatic actuators, base the decision on minimum air supply pressure. Electric actuators must be selected based on available voltage.

Industrial Valve Sizing and Selection Support

Carotek is an authorized distributor/representative of many types of industrial valves, including ASCO, DeZURIK, Flowserve, Valtek, Kammer and SVF. Carotek Application Engineers are specially trained to assist with ordering the right valve for your application.

Contact Carotek for expert assistance with your industrial valve sizing and selection process. Or browse our selection of industrial valves, process valves, and valve automation solutions to find the perfect fit for your application.

You might also see valves classified by function instead of design.

Common functional designations and their common design types include:

• Isolation Valves: Ball, butterfly, diaphragm, gate, pinch, piston, and plug valves
• Regulation Valves: Ball, butterfly, diaphragm, globe, needle, pinch, and plug valves
• Safety Relief Valves: Pressure release and vacuum relief valves
• Non-Return Valves: Swing check and lift check valves
• Special Purpose Valves: Multi-port, float, foot, knife gate, and line blind valves

Valve Sizing Explained: Keeping Things Flowing

While valves might be a small part of your piping process or system in terms of space, they&#;re often a substantial portion of the design and build budget. They also have a significant impact on long-term costs and overall system performance.

Choosing a proper valve size is essential to both optimizing costs and ensuring safe, accurate, and reliable operation.

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The first thing to consider is the overall size of the valve -- both in terms of physical dimensions and in terms of internal size and flow rates (CV).

Choosing a valve that does not fit properly in the space required could result in added costs. Choosing a valve which does not provide the ideal flow rate can lead to inaccurate flow control at the least and complete system failure at worst.

For example, if your valve is too small, it could cause reduced flow downstream while creating back-pressure upstream. If the valve is too large, you&#;ll find that flow control is drastically reduced the further you move from fully open or fully closed.

When choosing the proper size, be sure to consider both the connector diameter and the overall flow rate of the valve compared to your needs. Some valves offer excellent flow while others constrict flow and increase pressure.

This means sometimes you must install a larger valve to adjust for flow than the adapter diameter alone might imply.

Valve End Connections: The Key to a Good Fit and Proper Operation

With sizing and design out of the way, it&#;s also important to consider valve end connections.

While the most obvious implication here is choosing an end connection compatible with your piping, there are also functional characteristics to common end types that might make one valve more suited to your needs than another.

Common valve connections and ends include:

• Screwed or Threaded: Often used in instrument connections or sample points
• Flanged: The most common ends for piping use
• Butt Welded: Typically used in high-pressure or high-temperature operations
• Socket Welded: Commonly used on small bore piping where threaded connections are not permitted
• Wafer and Lug: Often used for compact valves installed in systems with limited space

Valve Materials: Ensuring Safety and Long-Lasting Performance

Depending on your intended use, the materials with which your valves are made might be a critical aspect in ensuring safe operation and reducing maintenance and replacement costs over the life of your operation.

Stainless steel valves are excellent options in a range of processing environments, including those involving corrosive media (such as chemicals, saltwater, and acids), environments with strict sanitation standards (such as food and beverage manufacturing and pharmaceuticals), and processes involving high pressure or high temperatures.

However, if you are processing solvents, fuels, or volatile organic compounds (VOCs), choosing a valve material from a non-sparking material -- such as brass, bronze, copper, or even plastic -- is often a better option. In addition to selecting the correct body material, internal (wetted) trim parts should be evaluated for chemical compatibility as well. If your valve contains elastomers, they should also be evaluated for their chemical compatibility as well as pressure and temperature limitations.

Valve Standards: Meeting Compliance and Regulatory Concerns

Depending on your intended usage, you might find that valves must adhere to particular standards to meet regulatory requirements for safety, sanitation, or other concerns.

While there are too many standard organizations and potential regulations to cover in detail, common general standard organizations include:

There are also industry-specific standards to consider.

Major standards organizations by industry include:

• ASHRAE Valve Standards
• ASME BPVC Valve Standards
• ASSE Valve Standards
• ISA Valve Standards
• NFPA Valve Standards
• SAE Valve Standards

Final Thoughts

Choosing the right valve for your project might seem complex. However, by starting with general characteristics -- such as valve design, valve size and actuation method -- you can quickly limit your options to determine the best valves for your needs.

Whether you&#;re designing a new processing system or looking to make upgrades to or maintain an existing system, Unified Alloys&#; selection of valves and fittings can help you find the ideal solution for your application and usage environment. As a leading provider of stainless steel alloys, valves, flanges, and more, our experts have helped industries across Canada and North America for more than 4 decades. Need assistance or have a question? Contact us for personalized help.

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