Valves come in many sizes, materials and gate apertures to control the flow of air, fluids and solids. Determining a valve types involves the valve's size, construction, rated capability (pressure, flow rate, caustic resistance, etc.) and gate configuration. Valve selection in any application is always comparing price with performance. Installing an inexpensive valve may lead to early problems but installing a valve with over-rated performance characteristics can lead to budget shortfalls.

Determining the size of a valve

Valves are always measured by inside diameter. The outside diameter may vary depending on the wall thickness and material. A one-inch valve in a high-pressure application may appear much larger than a one-inch valve for low- or no-pressure installations. Don't confuse the overall size of a valve with its rate size. Valve size will also vary depending on the gate. A ball valve (a seated ball in a socket with a hole through the middle that rotates to turn on and off) will be larger than a knife-gate valve (a gate moving up and down such as a simple household spigot) because the mechanism for operating the valve is more complicated.

Determining the type of valve gate

Ball valves are used in high-pressure situations. A handle (or actuator) rotates a sealed ball installed in the line. A hole through the ball either allows the flow or shuts it off. Gate valves open and close like a door and are utilized to not only turn on and off a flow but also redirect flow to another line. Knife-gate valves are used to regulate the flow. As the knife-gate is raised or lowered the flow can be adjusted.

Determining the material for a valve

Valves come in many materials, ranging from steel and other metal alloys to plastic and even ceramic. The more caustic a material, the more exotic the material. Simple water valves can be brass, steel, aluminum or plastic. Valves handling acid or lime slurry will involve corrosion-resistant materials such as high-grade stainless steel, molybdenum and ceramic inserts. High-pressure ball valves are usually high-grade steel with stainless-steel ball inserts and seats.

Determining the type of valve for the application

Valves are manufactured to meet needs for hydraulic (high-pressure fluid), pneumatic (high-pressure gas) and solid materials. Whenever selecting a type of valve always determine the material the valve will control. As an example, a valve handling hydraulic fluid needs to handle very high pressures. A valve handling waster water incurs almost no pressure. Mixing valve types for unintended applications is almost always a sure-fire problem waiting to happen.

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Common Valve Types

Valve Types for Specific Services