Question on pipe sizing

HI,
I have an 18x36 IG vinyl pool and I am replacing my current filter and pump. The pool currently has 1.5" piping (2 suction-skimmer/drain and 3 return-stair jets/ pool and spa returns) The suction and return lines are connected with 1.5" Jandy valves.

Anyway, my pump filter and heater all accept 2" plumbing. Should I replace the existing 1.5" plumbing with 2"? It would be very easy to do since I have to redo it all anyway. Do the 1.5" Jandy valves restric flow? Will I notice anything different?

Thanks for any tips.
Joe

What you need to evaluate is whether replacing the suction and delivery piping above ground is worth it.

It's odds on that your suction piping from skimmers and drain are already 1.5", so increasing that is debatable. The delivery piping might be changed, but again you have to judge whether the changing this will will improve the flow dramatically. Any increase in flow will be seen at the suction side with possibly some cavitation. That is the main tradeoff.

Don't forget too, that the return jet nozzles will still be the same size, so that the restrictions will be there as well. You can increase the jet nozzle sizes, to reduce that restriction, but then the suction side will really start showing signs of cavitation.

I would say that if you have adequate flow with the existing setup, leave it alone. i.e. If it ain't broke, don't fix it.

Hope this helps.

Pat

Well, I was thinking that since I can pull water from 2-1.5" lines and distribute via at least 2-1.5" lines (albeit through 1.5" valve) that putting 2" plumbing may be beneficial. It all works fine now but since I have to replumb anyway I thought I'd consider it but if it's going to cause problem then forget it.

FWIW, I will be putting in a 3/4 HP Whisperflo that moves 70gpm.

From a hydraulics standpoint, 2 1.5" lines in parallel are equivalent to a single 2" line so it would make sense to increase the pad plumbing to 2" to minimize head loss.

Also, cavitation is caused by suction side restriction. Increasing return restriction or reducing suction side restriction will decrease the possibility of cavitation.

Sounds good Mark. I'll order a 2" multiport valve then. If it doesn't work I'll just redo it with 1.5" and reducers but I don't think I'll have an issue.

Would the change to 2" have a significant impact on head loss or not really?

If you change both the suction and return sides to 2", I doubt you would get more than 5 feet of head reduction and more likely to be 2-3. You would have to do a full head calc on the plumbing you have to know for sure otherwise you won't really know until you do the change.

I figured as much. It can't hurt to go to 2" so I'll plan on that.

Thanks!!!

Did you mean that you're going to replace your Jandy 3 way diverter valve or a sand/de filter multiport valve? Your current Jandy 1.5" valve should also accept a 2" coupling on the outside of the valve for connection to your new 2" pipes, eliminating the need for a new valve. Just cut the old 1.5" pipe flush with the valve. If you're a good plumber, you can peel off the old 1.5" pipe remnant, but that's another post.
I don't think you're going to gain significant flow rates but you will gain some efficiencies by going to the 2" pipes. Your pump will run cooler too, which helps to extend the motor life.