manual throttling of plug valve

[engahmedbahgat]

Hello,

I would like to ask if it is possible to use plug valve in manual throttling service and keep it partially close for a long times like 2 or 3 months in gas service ??
if not, what is the suitable type of valves can do that


thank you in advance

 

[LittleInch]

Plug valves are commonly used for this operation, but others include globe valves, needle valves or plug and cage control valves. Any valve held steady at a single point may well suffer from damage due to high velocity erosion within the valve itself and hence would slowly "drift" away from it's original set point. All depends on how course your control function is.

Given that unless the inlet and outlet conditions stay exactly the same (pressure, temperature, composition) the pressure drop or flow rate will also vary even if the valve is not damaged. This is why control valves exist....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[moltenmetal]

If the gas is completely and utterly free of solids, and liquids, it could last a very long time.

If there are any solids or liquids, it might still last a long time, but it might not- it depends on how closed you're operating it, how much solid or liquid is present, and the nature of that solid or liquid content, and of course on the materials of construction of the valve trim and body.

The gas itself will not erode the valve parts.

Plug and ball valves without seat or hole characterization are rather difficult to use as throttling valves. They are very, very sensitive to the rotational position when nearly closed, and quite insensitive when nearly open. When using these valves for manual rather than automatic throttling, we generally put a gear operator on them, since trying to make adjustments with a handle alone is too frustrating to tolerate.

 

[zdas04]

As the previous posters have said, you certainly can create a flow restriction with a plug valve. The reason that they should not be used for control is "linearity". If I have a plug valve 5% open, and am getting 10% of full-open flow and then open it to 10% open, the flow will probably go to 40% of full-open flow. Another 5% open and flow will go to near 100%, further adjustments towards open will have no impact on flow.

Proper throttle valves like a globe valve, variable choke, or V-Ball will tend to be a lot closer to linear where I'm getting 8% of flow at 5% open and 12% at 10% open and 20% at 20% open etc. Much easier to program control.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[georgeverghese]

A lot depends on the trim of this plug valve if you have erosive service and / or high dp in throttling position. If this valve is in such heavy duty throttling operation, typical approach is to use stellite or tunngsten carbide surface hardened trims, and use a globe style trim - these are loosely called choke valves.

If you have sand in the gas in high dp application, then you will most likely have to replace this plug valve with a heavy duty choke valve.