In the simplest terms, a valve is a device used to control the flow of a medium ' liquid, gas or solid ' through a piping system. Most commonly, valves are used to stop and start the flow of media. Some valves are also able to control the rate of flow, these are commonly referred to as control valves.
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Because there are so many different uses for valves, they are available in a wide range of mechanical variations. Using the appropriate valve in a given scenario means your application will run smoothly and safely, accomplishing the intended goal most efficiently.
Though there are many different valve classifications, most valves fall within three categories: rotary, linear and self-actuated.
Rotary valves utilize a rotating closure component to block flow within a piping system. Most often, this rotation is limited to 90 degrees, which is why rotary valves are also commonly referred to as quarter-turn valves. These types of valves are closed at 0 degrees and open at 90 degrees.
Some rotary valves can operate with a larger degree of rotation and include more than two positions. Common examples of rotary valve types are butterfly, plug and ball valves.
Linear valves use a flow obstructer ' such as a disc, slat or diaphragm ' that moves in a straight line to start, stop or adjust flow through a piping system. These valves can be separated into two distinct types: rising stem (multi-turn) and axial.
Multi-turn linear valves work particularly well in control applications and include globe valves, gate valves and needle valves. Axial valves, such as coaxial and angle seat valves, are fast-acting and used primarily in on/off process applications.
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Compared to other categories of valves, linear motion valves tend to have longer cycle times than rotary valves.
Unlike linear and rotary valves, self-actuated valves do not require direct input from the operator. Instead, they use the pressure within the process line to open or close a pressure control valve. This valve type is commonly used as a pressure relief valve and only opens once maximum allowable pressure is reached within the system. As a result of this mechanism, self-actuated valves are common safety requirements in certain applications.
Common self-actuated valves include relief valves, safety valves, check valves and steam traps.
Ball valves are commonly found in newer homes. They use a handle to control the placement of a hollow, perforated sphere in the mechanism. When the handle is turned, the hole immediately opens or closes the water flow.
You can tell by the handle placement whether the valve is opened or closed: when it is in the open position, the handle lies flat, in alignment with the flow, and when it is closed, the handle is perpendicular to the flow. They are often used for shut-off and control applications.
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