Pentair VSF flow rate out of callibration?

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UCFKnights

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Jun 16, 2018
16
Orlando, FL
Last year, in the middle of pool season, we a pump fail and need replacement and I had an Pentair Intelliflow VSF-XF 3 HP pump installed. When it was setup, the flowmeter after the pump on the return line to the pool was also replaced (2" pipe, 2" flow meter). From when the pump was installed, it pretty much always reads "pressure limit" if you set the pool to a little above its required flow rate of 100gpm and seems to just run at maximum speed, but when its there, the flowmeter on the pipe reads 140 gpm. I then just turned down the flow speed until I got the flowmeter in the PVC pipe down to 110 gpm where I wanted that, and I've had to basically set the VSF to run at 65gpm to get 110gpm out of it.... its very reliable at that, it speeds up as the filter gets dirtier and keeps the same flow rate, and drops the speed of the pump back down with clean filters...

its working fine, other then me having to set the VSF to 65 gpm, but I'm curious as to what is wrong and how to fix this issue? From the look of the water flow, it appears the Pentair flow meter is wrong, and the PVC one is correct (and verified by putting the old PVC flow meter back in, which gave identical readings to the new one)
 
The VSF pump does not have a flow meter. The flow is calculated based on the power the motor draws. It is an approximation at best.

I also doubt that you are pushing 110-140 gpm through a 2" pipe.

The pump flow sounds more reasonable for a 2" pipe then your flow meter.

A man with one watch knows what time it is; a man with two watches is never quite sure.
 
UCFKnights said:
I'm sorry, it was a 3" pipe, this is the flow meter installed: https://www.amazon.com/gp/product/B007CU0QI2/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
Click to expand...

What filter and heater do you have?

Your filter and heater don't have 3" pipe and are restricting your flow even if the rest of your pool pad is plumbed with 3".

UCFKnights said:
How does the pump automatically speed up as the filter gets dirtier if it doesn't have any built in flow meter?
Click to expand...

The pump sees a drop in motor load when the filter gets restricted and flow drops and increases the RPM to maintain the flow.
 
UFC,

Running in the Flow mode rather than in the RPM mode is not needed by 95% of pool users, but unfortunately most of them think it is some kind of requirement.

It just makes the simple, much harder. You are a great example. If you only had a VS pump, you would never come here to ask your question.. :mrgreen:

I always suggest that a new VSF pump owner initially set up their new pump as all VS. Then run it for a year and see how it works. After a year, if you can find anything you can't do, then make whatever changes you want.

Thanks,

Jim R.
 
I guess you entered my question, there is no real flow meter so the VSF flow rate is probably entirely inaccurate since its just based on RPM and presumably some flow restrictions?

Sorry, forgot to mention this is a commercial pool, it has a required flow rate on the permit to be open. It has DE filters discs in a tank
 
UCFKnights said:
Sorry, forgot to mention this is a commercial pool, it has a required flow rate on the permit to be open. It has DE filters discs in a tank
Click to expand...

Then let the numbers on the flow meter make any inspector happy.
 
The VF pumps use RPM and Watts to determine the flow rate. These three variables (RPM, GPM, Watts) are unique at each value so are fairly accurate (~10%).

However, the flow meter that you have is about 10% accurate at full scale which means it can be as much as 30 GPM off over the entire range. Plus they get even more inaccurate the closer to a plumbing fitting they get. Not worth the trouble IMHO.
 
mas985 said:
The VF pumps use RPM and Watts to determine the flow rate. These three variables (RPM, GPM, Watts) are unique at each value so are fairly accurate (~10%).

However, the flow meter that you have is about 10% accurate at full scale which means it can be as much as 30 GPM off over the entire range. Plus they get even more inaccurate the closer to a plumbing fitting they get. Not worth the trouble IMHO.
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Thanks, but the thing that irks me is its even more then 30 GPM difference, I'm looking at 55 GPM off. I'm a little confused by your phrasing, since you said the pumps fairly accurate (10%) then said the flow meter is 10% accurate which is extremely inaccurate, are you saying the pump is 90% accurate and the flow meter is like 10% accurate? The phrasing makes it sound like 10% margin of error from the pump is good, and the same 10% margin of error from the flow meter is bad.

There's about an 8 foot section of pipe that is straight where the flow meter is centered on it, so I'm not sure how much that effects its accuracy?

Even though the pool has no signs of problems, I'm now even more curious if the inaccurate device is the flow meter, or if its the pump. While I understand TFP seems to say "flow rate/turnover rate doesn't matter" it is required by code in my state (Florida) and I do wish to have the pool in compliance. While the health department is perfectly happy with where the flow meter is reading, I wish to have it actually be in compliance as well. I guess my next test is to shut off the return lines to the tank, and drain the tank using the pump and seeing how long it takes for the pump X gallons out of the mixing tank. The weather isn't looking good for the next few days but I'll post that update for anyone interested when I get it done
 

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UCF,

Our turnover advice is for residential pools. You are trying to comply with the law in your area, which makes perfect sense to me. Something you need to do.

As long as your inspector is happy, I doubt that the actual turnover rate makes much difference.

Let's see if Mark can clarify his comments.. Calling @mas985

Thanks,

Jim R.
 
Jimrahbe said:
UCF,

Our turnover advice is for residential pools. You are trying to comply with the law in your area, which makes perfect sense to me. Something you need to do.

As long as your inspector is happy, I doubt that the actual turnover rate makes much difference.

Let's see if Mark can clarify his comments.. Calling @mas985

Thanks,

Jim R.
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Yup, but also part of why I want to look at it, is if there is ever a new inspector and he looks at the Pentair flow rate instead of the flow meter, he could shut the pool down based off of that, and I won't really have a good answer for them as to why thats wrong. Also, occasionally if someone covers the route for the tech who usually cleans that pool for me, and sees the flow rate at 65 GPM and enters that in our system, it automatically tells him to clean the filters and he could end up wasting time doing that prematurely.
 
UCFKnights said:
Thanks, but the thing that irks me is its even more then 30 GPM difference, I'm looking at 55 GPM off. I'm a little confused by your phrasing, since you said the pumps fairly accurate (10%) then said the flow meter is 10% accurate which is extremely inaccurate, are you saying the pump is 90% accurate and the flow meter is like 10% accurate? The phrasing makes it sound like 10% margin of error from the pump is good, and the same 10% margin of error from the flow meter is bad.
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The Blue White flow meter advertises the error at 10% of full scale which is around 30 GPM. But that is over the entire range of the flow meter even at very low flow rates. So percentage wise, it becomes a larger percentage error at lower flow rates.

However, the calculation done by the Intelliflo has about a 10% error at all flow rates but that is my estimate based upon experience not a published one.

So between the two, I would trust the Intelliflo over the Blue White.

If you want an independent flow meter with a bit better accuracy, then I would go with the FloVis. That is advertised at 2% error.


UCFKnights said:
Even though the pool has no signs of problems, I'm now even more curious if the inaccurate device is the flow meter, or if its the pump. While I understand TFP seems to say "flow rate/turnover rate doesn't matter" it is required by code in my state (Florida) and I do wish to have the pool in compliance.
Click to expand...
Turnover rate for residential pools is a requirement in Florida? News to me. Do you have a copy of the regulation that you can share?

This is for public pools only:

Most cities and states do have turnover requirements for public pools but these do not apply to residential pools.
 
mas985 said:
The Blue White flow meter advertises the error at 10% of full scale which is around 30 GPM. But that is over the entire range of the flow meter even at very low flow rates. So percentage wise, it becomes a larger percentage error at lower flow rates.

However, the calculation done by the Intelliflo has about a 10% error at all flow rates but that is my estimate based upon experience not a published one.

So between the two, I would trust the Intelliflo over the Blue White.

If you want an independent flow meter with a bit better accuracy, then I would go with the FloVis. That is advertised at 2% error.



Turnover rate for residential pools is a requirement in Florida? News to me. Do you have a copy of the regulation that you can share?

This is for public pools only:

Most cities and states do have turnover requirements for public pools but these do not apply to residential pools.
Click to expand...
Thanks for the information! I'm gonna do my test, and if it turns out the Pentair is more accurate I'll probably try changing to the FloVis. This is a commercial pool, not a residential pool, AFAIK there is no requirement on residential pools and I've never heard of any sort of required inspections on them either in regards to maintenance.
 
No flow meter. Take one apart and you will see there is no flow meter anywhere so the only thing the pump can do is calculate the flow rate. Parts list shows no flow rate meter either. Plus I have modeled this calculation many times and it is fairly accurate.

But are you saying that your pump shows the same flow rate for 700 RPM as it does for 1000 RPM? Is there any air in the pump basket?
 
Hey there - admin moved our convo over here: Pentair VSF flow rate Accuracy Question?

Lets pick it up over there.

But yeah it just doesn't add up to me. If it's using a calculation, why do other members who post say, the same X RPM, Y Watts, not ALL get the same GPM? People post here all the time with different numbers and even see those GPM's dramatically improve after changing something in the system (without necessarily a change in RPM or Watts). So something just doesn't add up.
 
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