A valve is a simple mechanism that opens and closes to control the flow & pressure of fluids and in scientific context, fluids include both liquids or gases - any substance that can flow freely. Valves are essential components of a piping system that conveys liquids, gases, vapours, slurries etc.
The simplest valves are the check valves i.e. one way flap mechanisms that allow flow in one direction & shut-off with back-flow pressure. In addition to running automatically, a valve can be operated through pressure, temperature, electrically or manually.
Manual valves are usually operated by levers, pedals, hand knobs or wheels to turn a screwed system. Large valves usually have a geared mechanism inside that actuate the disc against its seat. A valve may control fluid flow to one or often, as many as four ports according to the application. Valves come in different sizes from 0.1 mm to up to 5 metres for special applications. Valves are available in different set of materials too according to the requirement.
Types of valve available:
1. Gate valve
2. Globe valve
3. Plug valve
4. Ball valve
5. Butterfly valve
6. Check valve
7. Diaphragm valve
8. Pressure relief valve
9. Control valve
Each of these type has a number of models, each with different features and functional capabilities. Some valves are self operated while others manually or with an actuator or pneumatic or hydraulic is operated.
Functions of valves are:
1. Starting & stopping flow
2. Reduce or increase flow
3. Controlling the direction of flow
4. Regulating a flow or process pressure
5. Relieve a pipe system of a certain pressure
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