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Valves are used to handle a wide variety of functions in controlling the flow of liquids and gases. With so many options available, it’s important to look at all of the factors to ensure you are selecting the correct valve for your application.
1. Media Type
The characteristics of the liquid or gas type being controlled will determine the valve material that should be used. When monitoring harsh or corrosive materials, polytetrafluoroethylene (PTFE) and perfluoroalkoxy alkanes (PFA) are great choices, as they are able to withstand these conditions. When monitoring pressurized gases, it’s important to use metal valves for the highest level of safety.
2. Application Conditions
The selection of the correct valve sizing is the most important step in selecting the right valve for your application. An improperly sized valve can cause operation issues within the valve or elsewhere in the system. In addition to this, determine the temperature, pressure, and flow rate that your valve will be operating under. In most cases, metal valves can withstand higher temperatures and pressures than plastic ones.
3. Valve Function
Determine the need that your valve needs to fill. 2-way valves perform well for on/off control in a system, while 3-way valves can be used for on/off control, as well as for diverting or mixing media. Also, take note of whether your valve will be open or closed the most often. In order to extend the life expectancy, order a valve that is normally in that orientation and changes to the other direction when energized.
4. Actuation Method
Another consideration to be made is how the valve is to be operated. Identify if the valve will be manually hand-operated or if the valve will need to be actuated to turn off and on automatically. If the latter is chosen, decide whether the unit is going to be used with an electric, pneumatic, or hydraulic actuator.
5. Maintenance Requirements
If maintenance needs to be done regularly, ball valves are a great option as they resist clogging and are one of the simplest valve types to service. Ball valves are also available in 3-piece configurations, which consist of two end caps and a body. This allows the main body section to be easily removed for cleaning without disconnecting the end caps from the pipe, preventing the line from being shut down during maintenance.
The W.E. Anderson™ division of Dwyer Instruments, Inc. produces a broad line of competitively priced valves and valve control products, including: globe, butterfly, ball, manifold, actuators, and solenoid valves. Each valve type has a variety of options to meet specific application needs. Valve position indicators, valve positioners, and electric or manual pneumatic actuators are also available for a complete valve package. To learn more about Dwyer’s valve product line, please visit our website.
In a previous post, we identified six factors that determine the sizing and selection of pressure relief valves:
Connection size and type
Set pressure (psig)
Temperature
Back pressure
Service
Rated capacity
In this post, we’ll explore six more factors you need to consider.
Applicable code compliance
ASME code compliance is a requirement for many pressure relief valves. This designation ensures that valves are designed, constructed, and installed according to the highest standards of safety.
The ASME V Stamp applies to all Section I valves.
The ASME UV Stamp applies to all Section VIII valves.
Any valve that you purchase or have repaired needs to bear all required stamps.
View Allied Valve’s ASME stamps.
Physical properties of the media to be relieved
Valves are rated for different service applications. For example, the Consolidated 1700 Series Safety Valve is rated for steam service, while the Kunkle Relief Valve Model 91 is rated for liquid. Some valves, like the Kunkle Safety Relief Valve Model 140, are rated for air, gas, and liquid.
But service alone doesn’t tell the whole story. Liquids, especially, vary greatly in their physical properties, and these properties are crucial for determining the correct valve for your application. Here are the physical properties to consider for steam, gas vapor, and liquid.
Steam and Gas Vapor Liquid
Molecular weight
Density
Ratio of specific heats
Specific gravity
Compressibility factor
Viscosity
Maximum allowable seat leakage
All valves leak. Even valves labeled as “zero leakage” or “bubble tight” aren’t completely leak-free. The maximum allowable leakage rates for pressure relief valves is laid out in the American Petroleum Institute standard API 527. For valve selection, the maximum allowable leakage rate determines whether a metal- or soft-seated valve is appropriate.
Fire sizing
The ASME code specifies that pressure devices must be protected against overpressure due to external fire. Fire can change the media in the device (for example, a liquid may transform into a gas) and the valve must be equipped to handle it. Fire sizing determines the capacity of the valve in a fire situation by allowing for greater overpressure.
Installation area and requirements
The available installation area may constrain the valve size and configuration.
Extreme environmental conditions
Environmental conditions such as extreme heat and extreme cold can affect the operation of pressure relief valves. Make sure the valves you select are capable of withstanding the conditions in which they will operate. (Learn how to winterize valves and actuators.)
Our valve experts are on hand to answer any questions you may have about sizing and selecting pressure relief valves. Contact us today.
Source: Kunkle Safety and Relief Products Technical Reference
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