Introduction of valves
A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways.
what valve functions:
- stopping and starting fluid flow.
- varying the amount of fluid flow.
- controlling the direction of the fluid flow.
- regulating the downstream system or process pressure.
- relieving component or piping overpressure
The Types of Valves
The following is listed all types of valves.
Gate Valves
Gate valves used to start and stop the flow.
The valve is completely opened when the disk is removed from the flow stream.
Classification of gate valves is made by the type of disk used: solid wedge, flexible wedge, split wedge, or parallel disk.
Globe Valves
Globe valves used to start, stop and regulate flow.
The disk moves perpendicular to the seat to open or close the flow so the annular space between the disk and seat ring gradually changes. There are three body designs for globe valves: Z-Body, Y-Body, and angle and three designs for the disk: Ball Disk, Composition disk, and plug disk.
Ball Valves
Rotational motion valves used to start, stop or throttle flow. The valves use a ball-shaped disk with a hole in it. When the valve is opened, the hole of the disk is turned in-line with the direction of the flow.
When the valve is shut, the ball is rotated so that the hole is perpendicular to flow direction.
Check Valves
Check valves or non-return valve are used in systems employing gate valves because they prevent the reversal of flow in the piping system and there is a low-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
Control valves
A control valve is a valve used to control fluid flow by varying the size 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 level.
Diaphragm valves
Linear motion valves that are used to start, regulate and stop fluid flow. The disk is flexible and seals with the seat in an open area at the top of the valve body.
Butterfly valves
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 on either a vertical or horizontal axis and is opened when the handle is rotated 90 degrees and closed when the valve is turned an additional 90 degrees.
Needle Valves
Needle valves have a long, tapered, needle-like point that is used to make relatively fine adjustments in the amount of fluid flow.
They are sometimes used as component parts for other valves because the needle allows for a gradual change in the size of the fluid flow opening.
Relief and safety valves
A relief valve opens slowly as the pressure increases about the set-point and only opens as necessary.
A safety valve rapidly opens as the pressure setting is reached and will stay open until the pressure is lower than the actuating pressure set-point.
Both valves are used to prevent damage by relieving accidental over-pressurized fluid systems.
