Difference in Cv for Full Bore Ball valves of different brands..

[hironorixq]

Dear Experts,

I was going through specifications of different brands of full bore ball valves and finds that the Cv values are all different? for example for a 3" full bore ball valves, one brand states 1300, another states 1000, and one states 600. All values are in Cv. Shouldn't typical full bore ball valves should be pretty similar and shouldn't have such drastic differences?

Best Regards,
Amateur Engrg

 

[katmar]

The inside diameter of a 3" Sch40 pipe is close to 78 mm, but you will find that the bore of the actual ball of a full bore valve can vary from 75 to 80 mm depending on the construction and pressure rating of the valve. But even allowing for this 600 does sound very low. For a generic 3" FB valve I would use about 1150.

However, unless you have a very critical application it is unlikely to matter. A typical Cv for a fully open 3" globe valve is 110, and even for a butterly valve it is about 330 - so the pressure drop introduced by your ball valve is unlikely to impact on the overall line hydraulics.

Katmar Software - AioFlo Pipe Hydraulics

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

 

[bcd]

Some of the confusion was caused by changes to the ISA standard that defines how to flow test and establish Cv. In one version, the theoretical flow loss attributed to thelength of pipe upstream and downstream of the valve was subtracted from the measured value, which inflated the resulting Cv. In another addition, they did not subtract the theoretical pipe loss. So the resulting Cv would be lower. Either way, when you calculate the flow loss in an actual pipeing system, the difference in Cv for full port ball valve is negligible. Just use the number the manufacturer has provided.