allows use of reduced flow capacity valves without reducers but you now have pockets to deal with, their use has to be coordinated with your piping layout and the overall design requirements
The original arguments for reduced bore (also called "normal bore") ball valves was twofold: (1) the reduced bore valves originally cost less; and (2) they had lower torque requirements than full bore. I started noticing that the price difference between reduced bore and full bore valves began evaporating in the mid-1990's and today it is rare to see full-bore priced higher than reduced bore, so that reason goes away.
The only time that the increased torque is a problem is if an actuator is sized very close to its maximum torque and you have to go up in size for the full bore. Most of the time you have so much safety factor built into your actuator that the same device works fine for either.
The dP across a reduced bore valve cannot be seen on most field measurement equipment (the beta ratio on a 10-inch valve is 0.8, on a 16-inch valve it is 0.875).
The big downside of reduced bore valves is that it is difficult to jam a pig through them.
Have seen the comment before that the price difference between full and reduce bore has eroded over the years. I don't agree with this statement. I realize it may be noticed, but is being influenced by low cost coutry sourcing. Valve producers in China need to produce in volume so many standardize on full bore and make a lot of them so the price of a full bore from China can be less than historically purchased reduced bore. For these companies in China, if you call up and ask for reuced bore, it would be a special order. When comparing full and reduced bore from the same manufacturer, you will get different pricing, especially as the valves get larger. Cost and torque were mentioned above, but another factor is weight. An 8" class 300 full bore ball valve weights from 1.5 to 2 times more than the reduced bore version. Someone has to pay for all the extra metal, and something has to support the weight difference in the pipeline. Use full bore if you need to for all the reasons mentiopned above (minimal pressure drop is essential, pigging, trapped water, etc.). Always use reduced bore whenever possible.
I have gotten pricing from mainstream U.S. valve manufacturers that indicated that many sizes of reduced bore valves were special order items and the lead time (and price) reflected this. It has been a few years, but the manufacturers were the big U.S. guys.
As to "always use reduced bore wherever possible" I would say that with increasing regulations to run smart pigs, "whenever possible" becomes "never" (because the government is taking jurisdiction over pipelines with alarming frequency).
bcd, The key words are "in pipeline construction", so in general I'll stick with my original comment and back up zdas' too, but now that smart pigging has been mentioned in conjunction with regulated pipelines, I will allow for continued reduced bore valve use in water and other unregulated pipelines that do not transport hazardous or potentially polluting fluids. Perhaps water pipelines and the public near their RoWs are happy to continue operating without the critical integrity data that instrumented smart pigs provide, and up to 50% product loss, but it is currently impossible for regulated pipelines carrying hazardous materials to continue to use reduced bore valves in their pipeline systems, and not cost effective either. Instrumented pigs provide a plethora of useful data for pipeline operators and their planning, insurance and maintenance staff, so it is still better by far to design for their use whenever possible, even if a system may be unregulated.
"I am sure it can be done. I've seen it on the internet." BigInch's favorite client.
What about the increased energy usage because the reduced bore valve creates a larger head loss. This may not be significant in a pipeline but in process plant with many valves to pipe length it comes into play.
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