Optimizing VS Pump

Welcome to the forum!

apav45 said:

I know many recommend the necessity of adding a flow meter to properly optimize flow(Gpm)/rpm/turnover.

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No one on this site should be making that recommendation since in general, we don't subscribe to the belief in targeting turnovers.


Most of use with VS pumps simply target the lowest RPM possible for the given task at hand.

apav45 said:

Before I install a $150 flow meter, is it possible to extrapolate out flow/rpm based upon my heat pump turning on at a minimum rpm?

What I found on my pool is that an rpm of 1900 activates the heat pump (fan & compressor) which requires a minimum Flow rate of 30gpm.

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That does not mean that the flow rate is 30 GPM. Most heaters have pressure sensors rather than flow rate sensors.

apav45 said:

If I raise the rpm to 1.5x1900 (2850rpm) can I assume my gpm would be ~45 at 2850, or it doesn't work that way?

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Flow rate is directly proportional to RPM so yes it works that way. However, as I mentioned above, you cannot assume 1900 RPM is 30 GPM.

But why raise the RPM by so much? 200 RPM above the minimum to account for the filter getting dirty should be sufficient.

Personally, I would not bother with a flow meter. They are very finicky when it comes to placement plus, you can estimate flow rate with pretty much the same accuracy as a flow meter.

Post back the following information:

Filter pressure at 3450 RPM?

Filter gauge height relative to water level?

Distance from pool to equipment pad?

Pipe diameter for suction side, pad, and return side plumbing?

Picture of the equipment pad would help as well.

Skimmers (17+36) 53'

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One skimmer is 17' away and the other 36'? That is not additive when they are in parallel.

Ok, so based upon the filter pressure (assuming it is correct and pressure goes to zero when pump shuts off), and your description of the plumbing. I get the following operating points:

3450 RPM, 49' head @ 44 GPM

Flow rate vs RPM = 44 GPM * RPM%

1900 RPM, 15' head @ 24 GPM

This indicates a LOT of head loss in the plumbing. The plumbing curve is the following:

Head (ft) = 0.025 * GPM ^ 2

This is between Curve A and Curve B which is very poor but I suspect it is due to the heat pump which tend to have very high head loss. Also, if you want to be above 30 GPM to meet the suggested minimum flow rate, the RPM should be around 70%.

If you open the bypass valve, what is the new filter pressure at full speed?

That is not normal. The pump may not be fully priming because of an air leak or the fact that the flow rate is so low.

I would put pool lube on all pump gaskets including the pump lid, drain plugs and inlet union. See if that helps.

It is also odd that the HP does not cause more than 2 PSI of head loss.

When was the last time you backwashed the filter?

When was the last time you broke down the DE filter and cleaned the grids?