PUMPS, VALVES & ACTUATORS OPTIMISING VALVE SELECTION –
a stamp of approval Joe Bush, Swagelok product manager, explains how the STAMPED method can help you choose the right valve for your industrial fluid system
reliably. Valves are one of the most important components, providing functionality that helps media flow through a system as intended. Since valves are often selected during initial system design, it is important to specify the right valve at the outset. But how do you identify the proper valve?
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The STAMPED method, which accounts for Size, Temperature, Application, Media, Pressure, Ends (or fittings), and Delivery, is a handy guide for making the right choice. Considering each of these operational conditions can guide you to the right valve choice.
ndustrial, piping, and instrumentation systems rely on using the right individual componentry to function properly and
However, the geometry of the valve’s flow path also influences Cv. For example, a needle valve can restrict flow, but a ball valve will offer on/off performance with minimal flow control. When in doubt, consult your manufacturer – a good one will help in sizing the valve you need.
T: Temperature Operational and ambient temperature will impact your valve selection. Consider whether these temperatures will be constant or variable, as these conditions may influence your choice. For example, continuous temperature
fluctuations may cause sealing materials to expand and contract. In addition, metallic
some ball valves may offer a throttling function, most are intended to be used in the fully open or closed position. A needle or metering valve would be a better choice for flow regulation.
M: Media The composition of your process fluid should influence valve selection. Ensure that system media is compatible with the materials that make up valve bodies, seats, stem tips, and other softer materials. Adverse reactions between materials and system media can cause corrosion issues, embrittlement, or stress corrosion cracking. These conditions can pose serious safety risks, as well as costly production issues. Also consider where your valve will be in
S: Size Valve size dictates flow capacity and should correspond to your system’s desired flow rate. Manufacturers provide a flow coefficient (Cv), which is the amount of water in U.S. gallons (or equivalent) per minute that will flow through a valve with a 1 psi pressure drop across the valve at 60°F (16˚C). Calculating Cv to predict flow is more complex for compressible fluids, but it is helpful to size valves for many applications. Generally, the larger the valve orifice, the greater the potential flow capacity.
8 FEBRUARY 2021 | PROCESS & CONTROL
components tend to lose strength at very high temperatures, reducing a valve’s operational pressure rating. If your application will be operating at extremes, verify with your manufacturer that the valves have been fully tested.
A: Application Do you need to control flow direction? Protect the system from overpressure? Start or stop flow? Regulate flow level? Your answers will guide your valve choice. Consider a two-way ball valve: Although
service. Valves operating outdoors, for example, are continuously exposed to weather elements. Choose valves made from materials that are best suited to operating factors to maximise their longevity and functionality.
P: Pressure When evaluating pressure in your valve choice, consider both design pressure and working pressure: • Design pressure is the manufacturer-
provided maximum pressure limit. Never exceed the design pressure of any fluid system component, unless doing so under controlled testing conditions. • Working pressure is the actual, normal
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