Downsizing the impeller

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Smykowski

Smykowski

TFP Expert
LifeTime Supporter
Sep 17, 2011
3,086
Gurnee, IL (North Suburban Chi-town)
I'm looking for some opinions from the pump wizards. I've got a Hayward S180T sand filter (150lbs) paired with a Hayward PowerFlo Matrix pump. It's a 1.5 hp motor, but it has the 1hp impeller installed. As I've been reading these pump forums over the last few days it seems more and more that I still have way too much pump for my filter. I was thinking about swapping out the impeller and installing a 3/4hp impeller instead. My thoughts are that my flow rate will slow which will improve my filtering (my pool gets really dirty with that fine dust in the summer), improve my electric bill, and reduce the load and thus improve the lifespan on the pump.

Is there any reason I shouldn't do this?
 
The reason you may have a 1 HP impeller is because the motor is up rated. Check the service factor and if it is below 1.3 (or isn't shown), then it is an up rated motor which is equivalent to a full rated 1 HP motor and they would both use the same impeller.

Also, it is fine to drop the size of an impeller but you may want to replace the shaft seal while you are at it.
 
Yes, the label reads SF 1.0, HP 1.5.

I've got the SP1515Z1E pump. The impeller that's on it is the 1.0 HP impeller, part SPX1500L. I'm looking at the 3/4hp impeller, part SPX1500F.

I guess the bottom line is, will that smaller impeller fit (shaft size the same, etc.), and is there any reason that switching lower would be a bad idea? Can I do damage, am I destroying efficiency, etc.?

Thanks again for all your help.
 
The impeller should fit. The thread is the same size.

It is usually a good idea to downsize an impeller as it will save energy costs (i.e. more efficient). However, it does reduce flow rate so if you have anything that is flow rate dependent, that could be affected.
 
Not sure if anyone is interested but here's a preliminary report....

Switched from the 1hp impeller to the 3/4hp impeller. Only ended up changing one seal. I was very careful with one and that one was reused. The other was corroded pretty good, so that was the one I changed. No leaks so far.

There is no noticeable flow rate difference. If I put my hand in front of a return after cleaning the filter, I can't tell the difference from last year.

However, when vacuuming with the larger impeller, I would get air in the skimmer basket and air in the pump basket, and I'm pretty sure it was air coming out of solution from the pressure drop. When vacuuming with the smaller impeller, I get no air in the pump and the suction is not noticeably lower.

The pumps are much, much quieter with the new impellers. My wife didn't realize I had turned them on when I did, whereas before, you could easily hear them from the house with the windows open.

Finally, we live in a very dusty area due to a horse stable about a half mile upwind from the house, and I was struggling with the "is it algae or is it dirt" problem. Both last year and this year I opened to a dirty non-swamp, and both years they cleared up in about a week of 8hrs pump time per day. The water seems to be as clear as last year, but this year the sediment settling to the floor seems to be less. I've had the solar cover on all week (it's 80 in April, but 65 in June, love Chicago weather), so I can't make a definitive judgement, but I can update in a week or two once the temp warms up and we really start swimming.

I haven't seen a power bill yet, but I think that even after spending $50 for two impellers plus shipping, if there's even a little bit of power savings, the improvement in the performance of the pumps and filters makes the project worth it. This is only my personal/anecdotal experience, so please don't take this as a TFP-wide endorsement, but if you have a situation where the pump is way over-sized for the filter (very common, it seems), downsizing the impeller would be a very simple, cost-effective way to improve efficiency without shelling out serious cash for a smaller pump or bigger filter.

@mas985, thanks for your help with this, your guidance helped me pull the trigger.
 
I am glad it worked out for you. Let us know if you notice a change in the energy bill. Also, are you changing run time at all?
 
Energy usage update:

June 2012: 1447kWh
June 2013: 1047kWh

July 2012: 1907kWh
July 2013: 1703kWh

I can't really remember what the weather was like this year compared to last year. I'm guessing that the pump usage is the big reason for the decrease. Part of the July savings was eaten by running the air a little more this July than last July (I think). My runtime is now at 8 hours, which is about an hour more than last year, and the total draw is still lower. I'll update in a few weeks when I get the August numbers, but I think putting the smaller impellers on is turning out to be a very good move.
 
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