​Introductions

​A control valves is a valves use to control fluid flow by varying the sive of the flow passage as directed by a signal from a controller.

​this enables the direct control of flow rate and the consequential control of process quantities such as pressure, temperature and liquid

​Definations

​A valve is a device that regulates, directs or control the flow of a fluid by opening, closing or partially obstructing various passageways.

​​The functions of valve:

•Stopping and starting fluid flow.

•Varying (throttling) the amount of fluid flow.

•Controlling the direction of fluid flow.

•Regulating downstream system or process pressure.

•Relieving component or piping over pressure.

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​Ball Valve

​Rotational motion valves, used to start, stop or throttle flow.

​the valves uses a ball shaped disk with a hole in it.

​When the valve open, the hole of the disk will be inline with the direction of the flow.

​When the hole is perpendicular with the direction of the flow, meaning the valve is close.

​Diaphragm valve

​Linear motion valve that are used to start, regulates and stop fluid flow.

​The disk is flexible and seals with the seat in an open area at the top of the valve body.

​Gate Valve

​Use to start and stop flow.

​the valve is completely opened when the disk is removed from the flow stream.

​Globe Valve

​Use to start stop and regulates flow.

​The disk moves perpendicular to the seat to open or close the flow so the annular space between the disk and the seat ring gradually change.

​Butterfly valve

​Its a rotary motion valves that can be used in on-off and throttling systems.

They are quick and easy to operate.

The flow control element is neither a vertical or horizontal axis and is open when the handle is 90 degrees and close when the valves is turned an additional 90 degrees.

​Needle Valve

​it has a long tapered, needle-like point that is used to make relatively fine adjustments in the amount of fluid flow.

​Check Valve

​Also known as NON-RETURN valve are used in systems employing gate valves because they prevent the reversal of flow in the piping system and there is alow pressure drop across the valve.

The pressure of the fluid through the system opens the system, while the weight of the check mechanism will close the valve if the flow is reversed.

​Relief and safety valves

​A relief valves opens slowly as the pressure increases about the set-point and only opens when necessary.

​A safety valve raphidly opens as the pressure setting is reached and will stay open until the pressure is lower than the atuating pressure set point.

​Both valve are use to prevent damage by relieving accidental over-pressure fluid systems.