TYPES OF VALVES (I)

Valves for fluid control, from the simplest shut-off valves to the various valves used in extremely complex automatic control systems, come in a wide variety of sizes and specifications. Here are several types of industrial valves. 

 

1. Gate Valve

Gate valves are used when a system on a pipeline requires "full on or full off" control and fluid flow can only be produced with minimal pressure drop. Gate valves are ideal and suitable If it don't regard to the control of fluid throttling. When used as a throttling, the fluid will flow at a high speed through the door seat, causing vibration and damage.

Gate valves are used as cut-off media. When it is fully open, the pressure loss of medium operation is the smallest. Gate valves are usually suitable for working conditions that do not require frequent opening and closing, or keep the gate fully open or closed. It is not suitable for regulating or throttling. For the high-speed flow medium, the gate vibration can be caused by the partial opening of the gate, and the vibration may damage the sealing surface of the gate and the seat, and the throttling will cause the gate to be eroded by the medium.

2. Globe Valve

Globe valve is called because the valve has a spherical shape. It is mainly designed for tight closing, frequent switching and throttling when the fluid has to control the flow. Its main characteristics are effective throttling, which minimizes the phenomenon of wire drawing and thus reduces the erosion of the valve and seat. However, because the valve seat is parallel to the streamline, the change of flow direction when the fluid flows through the valve seat will cause and the drop of force. It is only suitable for use when the head loss due to pressure drop is not required.

 

3. Check Valve

The check valve is a valve that automatically prevents the fluid from flowing backwards. The valve flap of the check valve is opened by fluid pressure, and the fluid flows from the inlet side to the outlet side. When the inlet side pressure is lower than the outlet side, the valve flap automatically closes under the influence of fluid pressure difference and its own gravity to prevent the fluid from flowing backward. The function of this type of valve is to allow the fluid to flow freely in one direction, and to limit its reverse flow. Any fluid reversal will close the valve, and the closing is completed, which depends on the spring.

 

4. Plug Valve

This valve is named after a plug with taper middle groove. Its structure is simple. It can be turned 90 degrees from full opening to closure. The flow port of the valve can be of any size and shape. It can have different flow direction combinations. Usually it is used for all-on or all-off, not for throttling use.

 

5. Ball Valve

Ball valves are evolved from plug valves. It has the same 90-degree rotation action, the difference is that the plug of the ball valve is a sphere, with a circular through-hole through its axis. The fully equal valve body cavity provides a small, straight-through flow path for the medium. The main features of the ball valve are its compact structure, easy operation and maintenance, suitable for general working media such as water, solvent, acid and natural gas, and also suitable for medium with harsh working conditions such as oxygen, hydrogen peroxide, methane and ethylene. The ball valve body may be integral or combined.

6. Cryogenic Valve

The cryogenic valve is used to transport liquefied gases in a freezer, usually in bronze or 300 series stainless steel. The cryogenic valve is different from the above common valves: first, the cryogenic valve has an extended bonnet, in order to have a sufficient air chamber to prevent the stem packing from freezing, which affects the operation and sealing, and reduce the heat leakage of the through valve stem. Second, when the closed cavities with double seats are closed internally, the discharge of liquefied gas must be considered to avoid excessive pressure during vaporization.

 

With the continuous development of valve technology, the application field of valves has been broadened, and the types of valves have become more and more.