Butterfly or Gate Valve for 30"diameter?

[Denob]

It seems that BFV's are cheaper than GV's at this diameter, but makes 'pigging' the line much more difficult. Any opinions on what to select if you are worried about: Initial cost , lifetime cost , and maintenance? I understand that BFV's are cheaper initially, but GV's may catch up when you consider the ability to clean the line and make the lifetime electricity bill of the pumps less expensive.

 

[JStephen]

I don't have the answer. But some other considerations- if you plan to use the valve for throttling, some valves work better than others (gate better than BFV, I think- check with valve manufacturers). Easy of use might be better with BFV than GV. And BFV will take extra fittings or long body if it's next to blind flange or another valve.

 

[UNLengineer]

It depends on the service of the valve, butterfly valves are better suited for throttling applications. Also, how often is the valve going to be operated. If the valve will be operated frequently, I would not suggest a gate valve as opening and closing a large gate valve can be quite a pain.

 

[LHA]

Gate valves should not really be used to throttle, it really beats them up...it even sounds awful.

Gate valves are excellent, and in my opinion, preferred, for isolation.

It depends what you are doing with each valve.

Remember: The Chinese ideogram for “crisis” is comprised of the characters for “danger” and “opportunity.”
-Steve

 

[rconner]

While perhaps sort of an ancillary aspect compared to the other features mentioned (and certainly not suggesting any more confined space work than absolutely necessary!), I suspect a 30" gate-type valve would be easier to crawl through and/or also get any sort of equipment through the valve/pipeline than a 30" buterfly valve, should this ever be necessary or desirable.

 

[ap76]

Also to consider that a gate valve can be rebuilt without removing it from the line. An MJ butterfly valve cannot. My experience with BFVs is that they usually fail in the open position, and therefore are useless when you really need them. The only way to make the valve servicable is to use a flanged one with adapters on either side, and when doing this the BFV should be in a vault.

This extra stuff usually drives the cost above the GV alone.

Also consider the cavitation effects on the BFV with respect to is proximity from changes in direction and diameter of the waterway. AWWA has a handbook on the subject of cavitation in a BFV