Butterfly Control valve

[sgasociate]

I have a 6" Jamesbury controlled butterfly valve installed in a 8" line supplying water to a tank. The line has conc. reducers on the inlet and outlet of the valve. The valve shaft is mounted horizontally. We are having wall failures on the bottom of the outlet conc. reducer due to cavitation caused by the valve. The system operates at 30 psi and a flow rate of approx 640k/hr. The valve usually opens only about 25%. The open side of the disk directs the water flow to the area of failure, but it is not erosion.Pictures indicate the roughness of cavitation, not the smoothness of erosion. The pipe system is carbon steel, A-106 & A-234 for the components.
Is there some diverter we can use to minimize the cavitation or do we need to change the fittings to another style or materials ?

 

[hacksaw]

you can put a restriction orifice (5-10 dia.) downstream of the valve. this will shift some of the d/p away from the valve. it is a problem with high recovery valves.

you need to limit the valve d/p to about 15-20 psi.

 

[BobPE]

if 25 percent is the max operating range, this is about on the limit of recommended butterfly throttling ranges and I would assume it spends most of its operating time closed even more. If you like that configuration, downsize the butterfly valve to allow it to open more that 25 percent as a minimum in the design operating range.

BobPE

 

[hacksaw]

Jamesbury has an excellent valve sizing manual that covers your case.

Nobody "likes" butterfly valves as such, but they can be made to work and work surprisingly well.

There are ways to deal with the cavitation issue without extreme modification of you piping, but you'll have to sort out the specifics with your valve rep.

BobPE raised a good point about controllability of a conventional disk. A characterized disk is certainly better suited for control.

 

[mtmurthy]

This is the problem with high recovery valves like bfly,ball valves. when cavitation damage has its effect
in the downstream of the valve. It is not recommended to keep the orifice plate at downstream (to avoid cavitation ,unless otherwise this is the only solution)when the valve is being used for control application.

can I have your system parameters, like inlet pressure, operating temperature,vapour pressure of your service.

 

[hacksaw]

I get 1280 gpm (sg=1 basis) at 30 psig inlet

the flow(velocity) in the 8" line is a bit high but is excessive for a 6" reduced section.

 

[BobPE]

hacksaw:

how deid you decipher 640k/hr???? I must have missed that in school, or I am going simple minded!! LOL

BobPE

 

[hacksaw]

kinda' guessing,

8" line has been good for 1000 gpm condensate/water in the past, then figured at 8.3 lb/gal and 60 min / hr...640K/Hr must be the lb/Hr flow...

sga needs to pull together the d/p and the specifics from his end. it should be interesting to see how it turns out.