Introduction to Valves: What Are Valves & How Do They Work?
Everything you need to know from valve types and standards to materials and uses
What Are Valves and How Do They Work?
At their most basic, valves are devices that work to control, regulate or direct flow within a system or process.
They often feature a range of characteristics that help to define their ideal application.
However, whether you’re looking to control flow, provide safety in a system that is piping liquids, solids, gasses or anything in between, there are likely stainless steel valves available to help.
Valves provide several functions, including:
- Starting or stopping flow based on the valve state
- Regulating flow and pressure within a piping system
- Controlling the direction of flow within a piping system
- Throttling flow rates within a piping system
- Improving safety through relieving pressure or vacuum in a piping system
Valve Opening Methods Explained
While many valves accomplish similar goals, how they do so mechanically can vary.
How a valve opens and closes will not only impact the overall performance but also determine how much control you have over the flow and how quickly the valve can operate.
Most valves fit into one of three categories:
- Multi-Turn valves: Think of these valves like a screw or piston. You crank the handle and the plug, plate, membrane, or other controlling obstruction moves into the path of the pipe blocking access. Depending on the valve, these can have higher or lower differentials allowing you to open or close them at various speeds.
- Quarter turn valves: Quarter-turn valves offer a full range of motion in a 90-degree turn of the handle. This makes them ideal for situations where precision isn’t as important as rapid action and easy opening or closing.
On top of the mechanical motion involved with a valve, also consider the method of actuation. In most cases, valves fall into one of three categories:
- Manual Valves: Typically adjusted by hand, these valves use handwheels, hand levels, gear wheels, or chains to actuate.
- Actuated Valves: Often connected to electric motors, air or pneumatic systems, hydraulic systems, or solenoids, these valves allow remote control and automation for high-precision or large-scale applications.
- Automatic Valves: Some valves activate when a specific flow condition is met. Examples include check valves closing during backflow or pressure release valves activating when an over-pressure condition is detected.
Common Valve Types and Their Applications
Valves feature a range of characteristics, standards, and groupings the help to give you an idea of their intended applications and expected performance. Valve designs are one of the most basic ways to sort the huge range of valves available and finding a good fit for a project or process.
Common types of valves include:
Predominantly equipped with quick-acting 90-degree turn handles, these valves use a ball to control flow to provide easy on-off control. Generally accepted by operators to be faster and easier to operate than gate valves.
Using a compact design, the butterfly valve is a quick-acting rotary motion valve ideal for tight spaces thanks to its wafer type design. Butterfly valve bodies are offered in many different configurations.
Used to prevent backflow, these valves are typically self-activated allowing the valve automatically opens when media passes through the valve in the intended direction and close should flow reverse.
As one of the most common valve types, gate valves use linear motion to start and stop the flow. These are typically not used for flow regulation. Instead, they used in the fully open or closed positions.
Knife Gate Valve
Typically used for controlling flow of media containing solids, the knife gate valve features a thin gate controlled through linear action which can cut through materials and create a seal.
While not suited for high-pressure implementations, these valves are ideal for use with grease, oils, paper pulp, slurry, wastewater and other media which might obstruct the operation of other valve types.
Globe valves are typically applied in modulating control operations. Typically avaialable in three body types, T-body (as shown above), Y-Pattern, and Angle body.
Typically used in small diameter piping systems when fine, accurate flow control is needed, Needle valves get their name from the point on a conical disc used within.
Often used for handling solid materials, slurries and liquids with suspended solids, pinch valves use a linear motion. Typically Pinch Valves feature an internal sleeve to isolate the media.
Using a quick-acting quarter-turn valve handle, these valves control flow using tapered or cylindrical plugs. They provide some of the best ratings when tight shutoff is essential and are reliable in high-pressure or high-temperature environments.
Pressure Relief Valve
Used to help improve safety, these valves are spring-automated and will help to return a system to the desired pressure during over-pressure events.
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.
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:
- CSA Group (CSA)
- The American Society of Mechanical Engineers (ASME)
- The American National Standards Institute (ANSI)
- The American Society for Testing Materials International (ASTM International)
- The Manufacturers Standardization Society (MSS)
- The International Organization for Standardization (ISO)
- The Public Health and Safety Organization (NSF)
- NACE International (NACE)
- The American Petroleum Institute (API)
- American Water Works Association (AWWA)
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
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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