“Service” is a critical piece of information for valve selection — it determines the type of valve you need, the valve material, and more. Here are some key pieces of information to have on hand when you’re deciding which valve you need for your specific application.
Type of service
When looking for the right valve, the more specific you can be about your service, the more successful your valve selection will be. For example, if you work at a food processing facility and need a pressure relief valve for an olive oil process, it won’t be helpful to define your service as just a “liquid.” The fluid properties of olive oil are different from other liquids like water or molasses, which means it might require a different valve than what you anticipate.
Service details that can assist with valve selection (liquids)
Density is a substance’s mass per unit volume. It’s a variable that can affect a liquid’s flow rate, so it’s a key piece of information for valve sizing. For example, the density of pure water is 62.305 lb/ft³, which has a different flow rate than mercury, a substance with a density of 844.9 lb/ft³.
Specific gravity is the ratio of the density of a substance to that of a standard substance. A typical standard liquid substance is water, and a standard gas substance, air. Both water and air have a specific gravity of 1.0.
Again, in some circumstances, the specific gravity of a substance can affect flow.
Another factor that can affect liquid flow is its viscosity, or thickness. For example, syrup has a higher viscosity than water.
Source: Wikipedia Commons
Service details that can assist with valve selection (gasses)
Molecular weight is the mass of a single molecule. This comes into play in valve selection because, generally, the higher the molecular weight of a substance, the lower the vapor pressure.
Specific heat ratio
Specific heat ratio is the ratio of a specific heat of a gas at a constant pressure to its specific heat at a constant volume. It is a key factor for selecting valves for gas services, as not all gasses flow the same as air.
The compressibility factor in gasses is a correction factor — it defines the deviation of real gas and ideal gas behavior. And as the compressibility factor changes, so does the reduced pressure of a gas.
Service details that can assist with valve selection (any application)
Operating and relieving temperature
Depending on the operating and relieving temperature of your service, you may need a valve made of different materials.
Take superheated steam as an example.
Superheated steam services are extremely common across industries, including pulp and paper, food processing, chemical manufacturing, and petroleum refining. Using dry steam is a sustainable way to conduct heat and energy in industrial processes. Although most steam valves are designed to accommodate saturated temperatures, superheated steam may reach temperatures that require different materials (or a different valve altogether), depending on the amount of superheat.
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