What is the right size?

Attached is the performance data for a Rain Bird PEB - when should it choose a 1.5" valve?  Certainly above 50 GPM, but if the site has the PSI, there's nothing wrong with using a 1" valve up to 30 GPM, right?  The system could automatically choose a valve with the lowest pressure loss, but that would then result in a 2" valve for 75 GPM.  So it is very much a designer decision, taking into account many factors.

In the Size Laterals dialog box, the valve size is right there, along with the associated pressure loss for each size.  The intention is that as you confirm the velocity and sizes for that zone, that you would also adjust the valve size if necessary.  We have discussed perhaps making the valve size more prominent, perhaps a red highlight when the pressure loss is higher than another size would offer.  But even that could be rather annoying, looking like an error when it is an entirely acceptable usage case.

All of the relevant calculations are generated during the sizing, so the Size Laterals dialog box is the most sensible place to add any additional logic or visual highlights.

--J

Totally understand the valve size is somewhat of a judgment call based on the desiger's opinion and system pressure since it's not black or white. Could there be a way to set min/max allowable PSI loss parameters it could use to size the valve (similar to setting the max allowable velocity preference)? 

Glad to hear it's been on your radar as well

That's certainly a thought, could have a max allowable PSI loss through the valve, above which the valve size will automatically upsize.

But then there is the whole pickle of, when you want to override that.  So, every time you size that system, it keeps trying to upsize the valve and you keep having to set it back.  Or it remembers that you manually set it once, and then never again tries to upsize that valve, even when it is connected to more GPM.

It's something we can continue to ponder, but having it all right there in the size laterals dialog box is still 90% of the solution -- it's literally right there in front of you at the exact appropriate moment.

--J