Pump too large for filter: Problem??

[catnip]

Transferred:
I need some help on pump and filter sizing and would appreciate any feedback anyone can offer.

We have a Pentair UltraFlow 1 HP full-rated pump feeding a Pentair Tagelus TA 60D sand filter. Based on the measured total dynamic head (using input vacuum and output pressure) of 56 feet with a clean filter, the pump is pushing 75 GPM through a filter rated for 60 GPM. I called Pentair and they say that 60 GPM is the maximum rate for this filter and either the pump or filter needs to be changed. My neighbor's setup is even worst off since he has a lower head and about 85 GPM through the same filter! (Gung Ho pool builders!!)

Both of these setups have been running for a few years without any obvious problems, but I'm wondering if we may have problems and not know it, e.g. less than optimal filtering, sand blow-by, etc. We did have to add a lot of sand (~60%) after about 5 years of operation, but I don't know if that normal or not.

Any advice from you sand filter gurus??

P.S. Based on the pool size, we could go down to a 3/4 HP full-rated pump pushing 60 GPM into a clean filter and have a 2X turnover in 10 hours, and there are no pool features that require a high volume. However, I would rather not replace either the pump or filter unless really necessary.

 

[catnip]

Transferred reply from Duraleigh:
Hi, Chuck,

There's some pretty smart engineer types floating (no pool-related pun intended) around here that can give more scientific insight but:

A: you could reduce flow by restricting a valve on the return side of the system. That would cause your pump to work a little harder and use more juice(not good) but would slow down your gpm.

B: you could restrict the suction side of your pump as well. Your GPM will go down as will electrical consumption. Folks that know a lot about pumps don't generally like to do that......I'm not smart enough to know why, tho.

C: you could explore turning your pump into a two-speed (I think that's doable....not sure) or, perhaps best of all, place a smaller impellor on the pump which will solve the issue.

I wouldn't be in a rush to solve this common situation but you certainly don't have an ideal configuration.
_________________
Dave Smith