Valve Function
Valves are a part of many daily- used machines and can perform a variety of functions. The three common valve functions include stopping and starting flow, throttling (control) flow, and acting as a non-return check for flow (check).
Stop/Start valves are used for systems that do not need the flow throttled. The valve opens to allow the flow and closes to stop flow.
Throttle or control valves control the speed and capacity of flow through the system.
Non-return or check valves control the direction of flow. Flow in the desired direction opens the valve, while flow in the oppose direction forces the valve closed. These valves are important for preventing backflow to systems in applications such as wastewater management.
Method of Control
The mechanism to control flow can vary based on the application of the valve. In general, there are two means of controlling flow through a valve.
Linear motion valves use a closure member that moves in a straight line to allow, stop or throttle the flow. The closure device could be a disc, slat or flexible material, like a diaphragm. The closure device can be used to:
Move a disc or plug into or against an orifice
Slide a slat, cylindrical, or spherical surface across an orifice
Move a flexible material into the flow passage
Rotary motion valves rotate a disc or ellipse about an angular or circular shaft extending across the diameter of an orifice. Quarter turn valves will be in their fully open or fully closed state after a 90° turn of the stem.
Types
Below is a summary of the basic and most common types of valves, more information can be found by clicking the link in their title.