Valves are mechanical devices that block pipes either partially or completely to change the amount of fluid that passes through it. A valve can also regulate gases as well as liquids. It is important for valves when they are switched off to allow absolutely no escape of liquid or gas through a pipe to avoid leakage. The seal on a valve needs to be perfectly secured which is why they are usually made of metal or plastic and have several different parts.

Valves are available in a selection of styles for the demands of various uses. All valves are designed to stop, allow or throttle the flow of a process of fluid. A gate valve for example is one of the original valve designs, these are ideally suited for on/off and primarily liquid uses. Another popular valve is a check valve. These types of valves only pass fluid in one direction which is essential for a variety of safety applications, as well as preventing overflow.

Other types of valves include lever ball, stopcocks and float valves.