A valve is a device that is able to control, shut off, direct, or regulate the flow inside a pipeline by obstructing its flow direction, partially or completely, depending on the type of application.
- Pumps are used to propel media through a pipeline, or increase the rate of flow of the media
- Valves can reduce or stop the rate of flow of the media
Check vs. Quarter Turn vs. Rising Stem
Check Valves
Check valves allow the media to only flow in one direction and automatically prevent backflow (reversing direction). Check valves work automatically and don’t require assistance to open or close. They are used on household sump pumps–they allow the pump to expel the water out of your basement and yet don’t allow the water to come back down the pipe.
Quarter Turn Valves
Quarter turn valves work on a simple principle where you turn the handle (and stem) a quarter of the way to open or close the valve. Common types of quarter turn valves are ball valves, plug valves, and butterfly valves.
Ball Valve
Plug Valve
Butterfly Valve
Rising Stem Valves
Rising stem valves have a threaded stem which is rotated to open or close the valve. As the stem is rotated, it raises or lowers the valve closure mechanism to allow media through or to close off the valve. Common types of rising stem valves are globe valves, gate valves, pinch valves (diaphragm valves are a type of pinch valve), and needle valves.
Globe Valve
Gate Valve
Pinch Valve
On/Off vs. Control Valve
On/off valves are used to either allow the media to flow through or to stop the media. They can be used to limit the amount of media going through the pipe; however, that is not their most efficient use and can even damage the valve. All valves can be used as on/off valves, but not all valves can be used as control valves. Gate Valves and Plug Valves should only be used as on/off valves and should not be used as control valves.
Control valves are used to control or limit the rate of flow. They are often attached to an electric or pneumatic actuator, which makes frequent, small adjustments to precisely control the amount of media going through. Rising stem valves are typically used as control valves because the rotating operation is slow and stable, making it easier to accurately control or limit the amount of media going through the pipeline. Except for Gate and Plug valves, most valves can be used to control the media; however, some are more efficient than others. The most common type of control valve is the Globe valve.
Ball and Gate valves are commonly used in home water pipelines. Note that the type of handle (green lever or red handwheel) may change; however, lever handles are normally only used with quarter turn valves. Garden hose valves are typically gate valves, so the flow of water can be controlled.
