Full bore = hole in the ball equals the pipe inside dia
Reduced bore = hole in the ball is smaller than pipe inside dia
Usually a process requires a well defined (or at least) pressure range to work properly. A valve, as other fittings, represents a minor pressure loss and must be taken into account when sizing a pipeline and a pumping system. The flow coefficients (Cv) of the two types of ball valves mentioned above are quite different (reduced bore valves have got smaller Cv).
There really is not a process reason to select a reduced-port ball valve over a full-port ball valve. There is a measurable dP across a reduced port valve, but work done at Southwest Research (for gas measurement, but the concept carries over) showed that with the beta ratio of a reduced port valve virtually none of the (small) dP is "permanent". That means that if you measure the pressure 10 diameters upstream and 10 diameters downstream of a reduced port ball valve in the same flow you will get essentially the same dP (down to a fraction of a mm of water column) as a full port valve.
OK, if there is no process reason, why would you pick a reduced port valve over a full port? Historically, the reason has been cost. For some reason, prior to about 1990 there was a significant cost savings for reduced-port valves. That stared to change around 1990, and by 1995 you had to look very closely at your cost estimates--in some sizes the reduced port valve was actually more expensive than the full port valves. It is still true today. Even when the reduced port valves are cheaper it is usually a pretty small difference. On the other hand, it can be really hard to get a pig to scamper through a reduced port valve, and you cannot run a smart pig through a reduced port valve.
If you can say that the cost is a wash, then I can not see any reason why you would ever buy a reduced port ball valve.
Now if you were asking about selection criteria between a full port "floating ball valve" and a full port "trunnion ball valve" the discussion gets more interesting, but you didn't ask that.
We have a bypass line for a 1" control valve. The control valve is used to drain liquid from a vessel. Upstream pressure is 850 psig and downstream is 10 psig. So 840 psig pressure drop. In case of failure of this control valve, we need a bypass line and a manual valve. What should we use ? In the past we have used a Globe valve but in a recent event when we had to open it for the first time it shook and screamed and we had to change the bonnet. The medium flowing is hydrocarbon gas and collected liquid.
Ansh93,
You will probably get a better range of responses by starting a new thread instead of hijacking this one. You might be surprised at the range of answers if you are careful to create an interesting subject line. This thread is tired and not many people open it anymore.
