Pump speed questions

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WillAP1

Member
Dec 7, 2021
12
Tallahassee, FL
Pool Size
35000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Hello TFPers,

Not long ago I had a new Pentair VSF pump and intellicenter automation system installed. The installer setup the schedule to run at a very high speed (3400 rpm) for 12 hours a day. After doing some research here I realized that wasn't necessary from a filtering/chlorine production standpoint so I bumped it down significantly to 1800 rpm to save some money on electricity. The pool is clear and balanced and seems to be generating/maintaining chlorine fine, however I did notice something that I wasn't sure if should be a cause for concern or not.

It looks like more air is getting introduced to the system than before. Previously I had gone through and found some plumbing leaks and thought I had them all addressed. When it was running at high speed I had no issues with air getting introduced after these fixes. The pump primed quickly and there was very little to no air showing through the pump lid. However, running at lower speed there is quite a bit of air showing in the pump lid and if I turn it up to full speed it blows a lot of large bubbles out of the jets for several minutes. After putting it back down to low speed the air will eventually come back.

Is this a problem or just an expected effect of running at a lower speed? The pump seems to be operating fine (not cavitating) but the GPM reading does go down over time. I understand this is not really important (and maybe not an accurate reading due to the extra air?) but my worry is that the flow rate could get low enough to have a negative effect on my salt cell producing chlorine.

Any thoughts?

While I have you here: Also, I have a booster pump that runs a Polaris pressure side cleaner. Should I be running my main pump at high(er) speed while this is on or can/should I leave it at 1800 rpm? Not sure if that will effect performance or not.

Thanks,
Will
 
WillAP1 said:
However, running at lower speed there is quite a bit of air showing in the pump lid and if I turn it up to full speed it blows a lot of large bubbles out of the jets for several minutes. After putting it back down to low speed the air will eventually come back.
Click to expand...

That is normal behavior of VS pumps running at lower speeds.

WillAP1 said:
The pump seems to be operating fine (not cavitating) but the GPM reading does go down over time. I understand this is not really important (and maybe not an accurate reading due to the extra air?) but my worry is that the flow rate could get low enough to have a negative effect on my salt cell producing chlorine.
Click to expand...

GPM goes down over time at a set RPM because the filter is getting dirty and more restricted.

Your salt cell will continue producing chlorine as long as the flow switch is engaged. GPM does not effect chlorine production.

WillAP1 said:
While I have you here: Also, I have a booster pump that runs a Polaris pressure side cleaner. Should I be running my main pump at high(er) speed while this is on or can/should I leave it at 1800 rpm? Not sure if that will effect performance or not.
Click to expand...

If your Polaris is running fine with the VS pump at 1800 RPM then all is good.
 
ajw22 said:
That is normal behavior of VS pumps running at lower speeds.
Click to expand...
Good to know. Thank you. That is what I was hoping.


ajw22 said:
GPM goes down over time at a set RPM because the filter is getting dirty and more restricted.
Click to expand...
That makes sense however this is a repeated range over the span of multiple days without cleaning the filter in between so I wouldn't think that would apply to this.

For example: Monday at 9am its running at 36gpm and by 11pm its down to 24gpm. Tuesday at 9am its back up to 36gpm and down to 24gpm by 11pm again. Same for Wednesday, Thursday, etc. without any cleaning of the filter.

ajw22 said:
Your salt cell will continue producing chlorine as long as the flow switch is engaged. GPM does not effect chlorine production.
Click to expand...
Right, but the flow switch has some non-zero limit and GPM is a measure of flow so the two are related, correct? For example if my flow switch disengages at 25gpm and my pump gets down to 24gpm over time then I'm not producing chlorine, right? This is my concern.

ajw22 said:
If your Polaris is running fine with the VS pump at 1800 RPM then all is good.
Click to expand...
Ok thanks.
 
The point of a VSP is to operate at the slowest speed that still satisfies your pool's requirements (closes flow switch on SWCG, skimmers work, etc.). It takes a little trial and error since each pool is different. Gradually slow the pump until the SWCG flow switch opens. Note that RPM and add 100 to give yourself a margin. I run 24/7 at 1000 RPM, which draws ~75 watts. It costs less than $6/month in electricity. I like constant skimming, chlorination, filtering, and circulation.
 
WillAP1 said:
For example: Monday at 9am its running at 36gpm and by 11pm its down to 24gpm. Tuesday at 9am its back up to 36gpm and down to 24gpm by 11pm again. Same for Wednesday, Thursday, etc. without any cleaning of the filter.
Click to expand...

What type of filter do you have?

Please create your signature with details of your pool and equipment so we don't need to aqsk these questions to answer your questions.

Every time you turn off your pump the dirt slumps down in the filter and clears part of it. So when you turn your pump back on you get a high GPM. As the filter runs the dirt coats the filter, restricts it, and the GPM lowers. Until you turn the pump off and the cycle repeats.
WillAP1 said:
Right, but the flow switch has some non-zero limit and GPM is a measure of flow so the two are related, correct?
Click to expand...

Find the RPM where your SWG flow switch just turns on. Set the minimum RPM for your pump to be that RPM+200.
 
ajw22 said:
What type of filter do you have?

Please create your signature with details of your pool and equipment so we don't need to aqsk these questions to answer your questions.

Every time you turn off your pump the dirt slumps down in the filter and clears part of it. So when you turn your pump back on you get a high GPM. As the filter runs the dirt coats the filter, restricts it, and the GPM lowers. Until you turn the pump off and the cycle repeats.
Click to expand...

Sand filter. Not sure what brand or model. No markings on it from the outside. Might make another post to help identify it... would be nice to know what it is for the future if I need parts or when I'm ready to replace the sand.

I added info to my signature, thanks.

Ah ok. Thank you for the explanation. I had not considered this but it makes sense.

ajw22 said:
Find the RPM where your SWG flow switch just turns on. Set the minimum RPM for your pump to be that RPM+200.
Click to expand...
👍
 
Keep your filter questions in this thread. Change the subject line in the first post.
 
pjt said:
The point of a VSP is to operate at the slowest speed that still satisfies your pool's requirements (closes flow switch on SWCG, skimmers work, etc.). It takes a little trial and error since each pool is different. Gradually slow the pump until the SWCG flow switch opens. Note that RPM and add 100 to give yourself a margin. I run 24/7 at 1000 RPM, which draws ~75 watts. It costs less than $6/month in electricity. I like constant skimming, chlorination, filtering, and circulation.
Click to expand...

I would go one step further and determine if it takes the same RPMs to close the SWG switch as it does to keep it closed. It was different RPMs on my last pool. Not having the records anymore, I'll make up some as an example. Gradually slowing the pump, the SWG switch would open at 1000 RPM. Gradually speeding up the pump, the SWG would close at 1100 RPM.
 
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