Identifying Impeller by size?

[wpb]

Hi all,
I own three Whisperflo that I purchased as "remanufactured" pumps from a local company that is no longer in business.

The pumps have been working just fine, but I have some suspicions that the company may have taken some shortcuts when refurbishing.

When I recently went to do a pump service and replace all gaskets, I noticed two of the matching pumps have different sized impellers!

I purchased 1x 0.75 HP and 2x 2 HP Impellers.

Whisperflo sells a "1.5-2HP" impeller, which makes me think the reason the two pumps differ, relates to one of the "2HP" pumps being the *same motor* as the other, but having a "1.5-2HP" impeller.

The short version is...
I have three impellers, their cavity openings are roughly:
1/8" .... 7/32" ... 9/32"

Is there any site where it mentions the dimensions of the Whisperflo impellers? Or does anyone have any idea? I'm guessing they are 0.75, 1.5, and 2.0 HP, but I'd like to be sure before I order a second impeller to match.

Related topic: Increase Impeller on 2-Speed pump
Regarding the smallest pump, this is a two-speed pump that I intended to run at half-RPM.

This is an AO Smith B981 (3/4 HP x 1.67 SF = 1.25 SHP) with either a 0.75 or 1.0 HP Impeller (the 1/8" impeller mentioned above, not sure of the HP/model).

Problem is, once I wired it to run at half-speed, it didn't move enough GPM for my heater's flow-switch.

Considering this is a 1.25 SHP pump, would it be okay to go with a 1.5 HP impeller (WFE-6) at the *slow* 1725 RPM speed only? My goal is improving GPM without wasting power by running at full 3450 RPM.

Thank you in advance for any thoughts or ideas!!
RKM

 

[jblizzle]

Re: Identifying Impeller by MM?

I thought the impellers have model numbers on them or something. Not true for what you are seeing?

Are the motor HP and SF identical?

[s:3joqt71h]I think what you are saying should be fine to run a larger impeller ONLY on low speed (on high you will burn up the motor). This should increase the flow rate some, but will also of course use more power than the smaller impeller.[/s:3joqt71h] Better info from Mark below.

 

[linen]

Re: Identifying Impeller by MM?

If you look at inyopools site at the whisperflo pump parts they show dimensions when you open up each individual impeller (part #28). They have dimensions for the Outside diameter and total impeller width, but no detail on slot size. See: http://www.inyopools.com/pool_parts_pentair_purex_whisperflo.aspx There are 6 impellers on the whisperflo line afaik: full-rated hps of 1/2, 3/4, 1, 1.5, 2.0, 3.0

 

[wpb]

Re: Identifying Impeller by MM?

@linen - thanks for the tip! Unfortunately the outside dimension isn't helping, both the 7/32" and 9/32" (which I'm guessing to be 1.5 and 2.0 HP) are about 0.5" exterior width. The vane width is the big difference.

@jblizzle - I thought the same thing would be true! I have scoured these things for any identifying marks, finding nothing. I've also looked at all stock photos (using Google images) and cannot find any sign of a marking on any of the replacement impellers either. Seems odd, which is why I thought that I'd be able to find the dimensions with an Internet search, but no luck.

Yes, regarding the two 2HP pumps, they are identical motors (Emerson 2.0 HP * 1.1 SF)

One of the motors may have a limited life and I was considering replacing it with a larger 3 HP motor from a Whisperflo that I had also bought for the spa jets (before leaning here on the forums that 3 HP would be too much for 2" pipe).

Thanks again for your help -- if I eventually find the correct size for the interior water vanes, I will post an update so that others in the future will have the information!

 

[mas985]

Re: Identifying Impeller by MM?

Considering this is a 1.25 SHP pump, would it be okay to go with a 1.5 HP impeller (WFE-6) at the *slow* 1725 RPM speed only? My goal is improving GPM without wasting power by running at full 3450 RPM.

That would work only if the motor does not exceed the low speed amp rating. The problem is that the low speed winding is generally sized for the low speed impeller load so if you put a higher load even on low speed, it will overload the low speed winding. It may or may not trip the thermal overload but it could possibly burn out the winding.

One of the motors may have a limited life and I was considering replacing it with a larger 3 HP motor from a Whisperflo that I had also bought for the spa jets (before leaning here on the forums that 3 HP would be too much for 2" pipe).

Changing the size of the motor does not change the "size" of the pump. Putting a 2 HP pump on a 3 HP motor is still a 2 HP pump and will draw about the same power as the 2 HP motor. The motor rating is for maximum load only and not an indication of delivered power. That is dependent on the load (i.e. impeller).

What is the diameter (exact) of each of the impellers?

 

[wpb]

Re: Identifying Impeller by MM?

Changing the size of the motor does not change the "size" of the pump.

Exactly. That was the point. I have two 2 HP motors .. I have a backup 3 HP motor that I will use if one of them goes. I intend to use it with the 2 HP impeller to yield the same results albeit only slightly less efficient use of electricity (based on extensive reading here). I was not suggesting that I wanted to get a 3HP yield out of a 2HP impeller, just the opposite.

What is the diameter (exact) of each of the impellers?

All three are exactly 4.75". I can't measure to the mm because it would have to be done by sight due to no ability to flush-measure over the axle.

From all of the literature I see, it's common for the diameter to be exactly the same for the full range of WFE impellers. Only the water cavity or "vane" appear to be related to the sizing.

The problem is that the low speed winding is generally sized for the low speed impeller load so if you put a higher load even on low speed, it will overload the low speed winding.

Yep, my only reasoning was that because it's not a significant jump in SHP and because the head goes down (more than is proportionate to the RPM loss, or in other words, the same idea behind why a pump is more efficient at lower RPM) I might be able to get away with a small bump in impeller size.

I figured it was iffy, just wasn't sure if anyone here has done it / have feedback. My application is a 1000 gallon swim-spa (plumbed like a pool with heat pump, DE filter, etc). For this reason, I only run the recirc pump 40 minutes per day, although I'd bet this would still be enough to trip the thermal either way.

Thanks again for the ideas,
RKM

 

[mas985]

One other thing. I think the primary issue is that the heater's pressure switch is not being turned on. However, most heaters have pressure switches that can be adjusted so it should be possible to set the switch so it turns on at low speed but turns off when the pump is off. Of course, you just need to make sure it is meeting the minimum flow rate requirement too.


Since the motors you have are 2 HP up rated, the impellers cannot be larger than a 2 HP up rated impeller (1.5 HP full rated) or the motor would be overloaded and shut off. So the smaller of the two impellers must be a 1.5 HP up rated (1 HP full rated) impeller which is only one size larger than the 3/4 HP full rated impeller.

Also, I think the B981 is rated at 2.2 A on low speed which is about 500 watts. The 1.5 HP up rated would use about 440 watts and the 2 HP up rated about 445 watts so it would be close but it might work.

 

[wpb]

Hi Mark,
Ahh, excellent point on the impellers. Very helpful, thanks so much!

I had come to a similar conclusion, but not trusting the intellect of the rebuilder (seeing two different impellers) wondered if it might be the 1.5 and 2.0 (full rated) rather than 1.0 and 1.5. If you think it would have definitely shutoff with a the 2.0 full-rated Impeller on a 2.0 HP / 2.2 SFHP, then it's a good bet you've solved it.

If I'm reading the B981 docs correctly, you're right, 2.2A, so assuming I have 220v I believe it would be at 440 watts and be okay like you say, but will keep an eye on it to be sure (and report back).

I'm really fascinated that you can get wattage numbers for impellers, is there a location here on TFP that has wattage requirements for different impellers?

Thanks again, will report back with the findings!

 

[mas985]

Actually I misread the B981 spec sheet. It is rated at 115v and not 230v so the actual power limit is 253 watts so it will likely overheat. But double check the label for the actual voltage and amp ratings.

I based the power numbers from the APSP/CEC pump measurement data. The spreadsheets in my signature use this same data to estimate operating points for pumps.