Pump return piping and "looping"

[eljefe281]

My builder is one of the type which typically specifies a larger-than-necessary pump. I can't really blame him for that - his primary concern is building a pool that he's sure will work; energy efficiency is a secondary consideration for him.

Regardless, I have successfully talked him down off of that ledge.

He also specifies more pool returns/inlets than may generally be required.

That's OK, if your pump is oversized. There will be plenty of flow to ensure that each return has some flow through it.

I am concerned, however, now that I have arranged for a smaller, two-speed pump, that the returns at the end of the pool farthest from the equipment may become "starved".

I believe that this can be avoided by having the return piping configured in a continuous loop around the body of the pool. That will make the pressure the same everywhere in the loop and all returns will get some flow.

However, I read a little blurb in some article on the internet that one shouldn't set up the pool's piping like this. They didn't say why.

I would be mighty grateful if someone could share what they know about this subject.

Thanks ever so much.

[duraleigh]

There's folks here better at this than me but I don't think the loop will equalize the flow. The further from the pump, the more pipe friction you will have and resultant less flow. I may well be incorrect...others will chime in soon. Equalization could be easily achieved with the addition of valves on the individual returns.

My reason for posting is to remind you that filter size is MOST imprtant in designing your system. It is a good idea for your filter gpm to be in excess of your pump gpm. Maybe 15% greater and more is better. Don't overlook that relationship when choosing your equipment.

[eljefe281]

Thank you for the recommendation on the filter size. I believe I've got that nailed.

60 sqft DE with a 1 hp two-speed pump on a pool/spa with a total capacity of around 12,000 gallons.

There have been questions posted on here asking if it's possible to make your filter too big. Well, one consideration is to make sure that the pump is big enough to provide the required backwash flowrate.

I had some nut from Pentair trying to tell me that, because a 1 hp pump would deliver only 70 gpm at 65 feet of head, it wouldn't be large enough to meet the backwash requirement of 1.5 gpm/sqft (90 gpm).

I could feel my blood pressure rising as I tried to explain to him that, during backwash, the system resistance wouldn't be nearly that high.

[duraleigh]

I didn't know there was a backwash flow rate! Published, or someone's opinion?

[eljefe281]

This dude read it out of some manual, but I couldn't find one in the documentation on the Pentair website. It's entirely possible I overlooked it.

[eljefe281]

Bumpity-bump-bump.

C'mon, kids - help a brother out!

[mas985]

I don't think a continuous loop is necessary. You could simply use different size eyeballs on each return. Smaller ones closer to the pump and larger ones further away.

Also, if you ran separate pipe to each return from the pad, you could put ball valves inline and adjust the flow to each return.

Even if you did none of these things, the furthest return would only have slightly less flow than the others. When the pump is on low speed, the head loss is only 25% of that on high speed so pressure loss is very low and should equalize fairly easily between the returns.

[eljefe281]

Thank you.

That's very helpful, especially the part about different sized eyeballs.