Pump replacement questions

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diggler86

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Dec 25, 2013
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Looking to replace my current pump (AO Smith 3/4 HP, 1.67 SF) with a Pentair SuperFlo VS (P/N 342000). Currently run pump 4 hrs a day and water clarity is fine.

With the increased HP, is there any risk of damage to my other equipment?

FNS Plus 48 filter says OK to 96GPM.

The suction and return lines are copper, maybe 1.5"... these seem to be limited to 43 GPM. This seems to be an issue with a larger pump?

Not sure about the skimmer (U3) / main drain?

Would the new VS pump be ok? Maybe run full speed to prime only then back off? Install flow meter and set lower than 43 GPM?
 
Hello,
Where are you located? What are your electric cost?

You may be able to just swap out the motor for a 2-speed, run in low most of the time, save some money.

There's lot of hype on the variable speeds, but if your energy cost are low (less than $.30 KWH) it may be more cost effective to go with a 2-speed.

If the wet side is fine there's no reason to swap out the whole pump, a motor change may be more economical.
 
Located in Southern California. We have tiered electric. If I go above the 1st tier, the electric bill basically doubles to around $.30 KWH.

The variable speed currently have a rebate offering from the electric company, so I'd like to take advantage of that.

Primary concern at this point is compatibility with the pool & equipment - not breaking anything!
 
As long as you have no plans to integrate the pump into any automation systems, you should be fine with one of the smaller VS pumps. They are just not ideal if you have solar or other automation.
 
The U3 skimmer appears to be rated for 50-55 GPM. Its not so clear in the manual but it seems above that they recommend additional skimmers. The copper pipes would still be the limitation at 45 GPM. I guess its a recommendation, but is it recommended to avoid damage? Everywhere I look says you should not exceed 7 feet per second.
http://www.poolplaza.com/pool-pump-sizing-2.shtml

Filter PSI is about 12PSI when clean so that is 31 feet of return head. 75% of this is 24 for suction head. Total equals 55 feet head which is pool average and seems about right, although just an estimate.
http://www.troublefreepool.com/threads/16168-Calculating-Flow-Rate-From-PSI-Reading

According to this chart on page 26, at 55 feet of head, I'd end up with 65 GPM
http://www.pentairpool.com/pdfs/SuperFloVSOM.pdf

Which seems to be too much? This is where I am stuck with the logic.....

I guess its not that far off, and setting it for just a bit less RPM makes a significant difference, but again just want to be safe. If I underestimated and actually have 65 feet of head it would be perfect..
 
The recommendation is not to avoid damage. It is a rule of thumb to keep head loss relatively low. If you were installing new pipes, the recommendation would be to put in larger than 1.5" to keep the head loss low. But since your pipes are already in place, it is best to just live with the head loss you have. The Superflo VS will work fine with your existing pipes.
 
The only thing that can possibly be damaged is the filter but the VS will never deliver close to 96 GPM on 1.5" plumbing so that is not an issue.
 
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