October 07, 2008

Type of Valves - Gate Valve

It is very difficult for fresh engineers to understand the use of different kind of valves according to the process requirement. In which condition we should use a particular type of valve? What are the differences in each one of them.

To simplify the matter, I have compiled some information from different resources, which can be used by all of you.

Although many different types of valves are used to control the flow of fluids, the basic valve types can be divided into two general groups: stop valves and check valves.

Besides the basic types of valves, many special valves, which cannot really be classified as either stop valves or check valves, are found in the engineering spaces. Many of these valves serve to control the pressure of fluids and are known as pressure-control valves. Other valves are identified by names that indicate their general function, such as thermostatic recirculating valves.

Here I am discussing few basic types of stop valves and check valves.

Gate Valves
Gate valves are by far the most widely used in industrial piping. That's because most valves are needed as stop valves - to fully shut off or fully turn on flow - the only job for which gate valves are recommended.

Gate valves are used when a straight-line flow of fluid and minimum restric­tion is desired. The gate is usually wedge shaped. When the valve is wide open, the gate is fully drawn up into the valve, leaving an opening for flow through the valve the same size as the pipe in which the valve is installed. Therefore, there is little pressure drop or flow restriction through the valve.



Gate valves are not suitable for throttling purposes since the control of flow would be difficult due to valve design and since the flow of fluid slapping against a partially open gate can cause extensive damage to the valve. Except as specifically authorized, gate valves should not be used for throttling.

Gate valves provide optimum performance in conditions where high flow efficiency, tight shut off and long service is required.

Gate Valves are designed to operate fully open or fully closed. Because they operate slowly they prevent fluid hammer, which is detrimental to piping systems. There is very little pressure loss through a gate valve. In the fully closed position, gate valves provide a positive seal under pressure.

A gate valve usually requires more turns - more work - to open it fully. Also, unlike many globe valves, the volume of flow through the valve is not in direct relation to number of turns of handwheel.

CONCLUSION
Gate valves, while not designed for throttling or too frequent operation are generally ideal for services requiring full flow or no flow.

Gate valves are not designed for throttling.

In a slightly opened position high-velocity flow will cause wire drawing and erosion of seating surfaces in gate valves.

Repeated movement of disc near point of closure under high-pressure flow may gall or score seating surfaces on downstream side.

Slightly opened disc in turbulent flow may cause troublesome vibration and chattering.

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5 comments:

Anonymous said...

perfect explanation
thanx a ton

Anonymous said...

Very informative. Now I know why my gate valve doesn't shut off completely. Thank you.

gate valves said...

this looks like a very tough gate valve that would last for a lifetime.

plumbing said...

These are tough looking gate valves. Gate valves usually fail just because the installer has no idea what these types of valves are intended to do such as main steam shut off's or water mains. If properly used and installed correctly these valves last many years under extream conditions.

gate valve said...

Marvellous explanation. Thanks !

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