Chemical Forums
Specialty Chemistry Forums => Chemical Engineering Forum => Topic started by: coalball on November 02, 2009, 07:19:12 AM
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Dear all,
I'm working on a Water Injection Package for offshore platform (I'm in an oil and gas engineering design firm) and all of the isolation valves in that package are butterfly valve. Exactly what are the conditions that requires to use butterfly valve instead of the normal ball valve?
Thanks and regards.
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Hello coalball,
Good question! The answer I am giving will be generic, as there are always exceptions to the rule. Here are some general rule-of-thumbs. Any valve will work in any application....for a certain period of time ;) Every valve has its own limits.
Ball Valves:
1) limited to pressure on the plastic seats.
2) typically used for higher pressure applications
3) more expensive to construct
4) Is larger for the same pipe size
5) unrestricted flow when open
Butterfly Valves:
1) take less space than ball valves
2) form a tight closing seal
3) a rubber seated butterfly valve requires high torque to remove the vane from the seat
4) have lower pressure limits
5) typically used as control valves
6) less expensive
I hope this helps.
Best wishes,
Eugene
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I'd add that butterfly valve are more likely to fail than ball valves and when they fail they'll fail open.
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I would avoid using ball valves where the valve is being used to control flow rate.
My experience says ball valves are most effective as on/off valve.
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I'd agree with most of what eugendakin said, with the exception of their use as control valves, if by control he means modulating flow. This is sometimes done, but it is definitely not an appropriate use of butterfly valves. The flow characteristic for a butterfly valve is such that typically the valve would need to close 50% or more before seeing any significant reduction in flow. This implies that for most modulating control situations, the valve will only be operating at 20-35% open or so. This, by the way, is also mostly true of full-port or standard-port (uncharacterized) ball valves. However, a number of the ball valve manufacturers will install inserts into their ball valves to provide characterization to their flow profiles, and that can be tuned for specific flow applications. To my knowledge, this is not possible with butterfly valves.
That's not to say that a butterfly can't be used in special control circumstances, only that you should be aware of the limitations.
If by control he means on/off actuation, this is a very common and appropriate use of either butterfly valves or uncharacterized ball valves.