Valve is a device that controls the flow and pressure of the media. It’s an essential component of a piping system that conveys liquids, gases, vapours, slurries and even solids.

Some of the primary functions that valves perform are :.

• Stopping and starting the flow of the media
• Regulating the flow by reducing or increasing the flow of the media
• Control the direction of the flow o Mixing and diverting different fluids
• Achieving proper mixing of media with different temperatures and characteristics
• Act as emergency vents

Typically Valves categorised based below parameters :

• Type of Actuation
• Type of construction
• Classification on the basis of type of automation
• Pressure rating o Method of obturation
• Material of constructions of body and trim

Valves come in different types, models, Designs however here is an introduction to some of important components of the valve.

• Body -:
  The valve body is the primary boundary of a valve. It serves as the main element of a valve assembly because it is the framework that holds all the parts together.
• Trim -:
  Valve’s trim is a collective name for those parts which are normally exposed to media it carries. Typically trim includes a disc, seat, stem, and sleeves needed to guide the stem.
• Stem -:
  The valve stem provides the necessary movement to the disc, plug or the ball for opening or closing the valve, and is responsible for the proper positioning of the obturator.
• Seat -:
  The seat provides the seating surface for the obturator, Disc, plug, ball or wedge. A valve may have one or more seats. In the case of a globe or a swing-check valve, there is usually one seat, which forms a seal with the disc to stop the flow.
• Disc -:
  It is the part which allows, throttles or stops the flow, depending on its position. In the case of a plug or a ball valve, the disc is called plug or a ball, it is not used for throttling but it’s used for start or stop the flow.
• Bonnet -:
  The cover for the top opening in the body is the bonnet, and it is the second most important boundary of a pressure valve.

GGC is abbreviation typically used in process industry standing for Gate, Globe and check valves. Collectively these three valves are called as GGC Valves.

• Gate Valve –
  These valves are used isolate the flow of media i.e. to start or stop the flow, one of the most simple in construction, gate valves are relatively inexpensive and extremely easy to operate.
• Globe Valve –
  These valves are ideally used for regulating the flow of media. Globe valves have low cost of repair and used in cases where flow, Pressure or temperature has to be maintained at particular level.
• Check Valve –
  These valves are used to check flow reversals and allow the flow in only one direction. However, Check Valve needs careful installation and placement.

In Gate valve OS&Y stands for outside stem and yoke, this is most commonly used valve.

• A Yoke connects the valve body or bonnet with the actuating mechanism.
• A Yoke nut is an internally threaded nut and is placed in the top of a Yoke through which the stem passes.

Fail safe is a position which valves attain in case of a failure of Actuating force.

Fail-close: In-case failure of actuating force, valve gets automatically closed; this is the most common and widely required position.

Fail-open: In-case failure of actuating force, valve gets automatically open, for ex. Coolant which ensures temperature of media does not cross certain prescribed levels.

Cv is a flow coefficient of a valve, it gives us an idea of discharge capacity of a valve. Higher the Cv higher is the discharge capacity.

Control valves are valves, which regulate and control the flow of the media.