I have my ScreenLogic app set to rpm for my Intelliflo VSP. I usually have the pump rpm set to provide about 25 gpm. Over the last year the flow rate sometimes drops 1-3 gpm within a few days after setting it. Other times it doesn't change for a much longer time. When the flow drops I'll increase the rpm again to about 25gpm. But then a day or few days later the flow rate will have increased beyond 25 gpm by the amount I recently increased it. Is this operation normal? What causes the fluctuation? Is the flow rate monitored internally by the pump or an external flow sensor?
Fluctuating Flow Rate
- Thread starter djpool21
- Start date
21,
IntelliFlo VSF pumps operate in one of two modes..
In the RPM mode, the pump will run at a fixed RPM, but as the filter gets dirty, the flow (GPM) will go down.
In the GPM mode, the pump will run at a fixed GPM, but as the filter gets dirty, the RPM, will increase..
I say "as the filter gets dirty", but it could be anything in the water's path that restricts the flow... Normally it is the filter..
Thanks,
Jim R.
IntelliFlo VSF pumps operate in one of two modes..
In the RPM mode, the pump will run at a fixed RPM, but as the filter gets dirty, the flow (GPM) will go down.
In the GPM mode, the pump will run at a fixed GPM, but as the filter gets dirty, the RPM, will increase..
I say "as the filter gets dirty", but it could be anything in the water's path that restricts the flow... Normally it is the filter..
Thanks,
Jim R.
Thanks Jim. So would you say the fluctuations I'm seeing are normal operation as the filter gets dirty?
21,
Generally, things get worse as the filter gets dirty...
Something has to happen for things to get better, like backwashing your filter..
If you are not doing anything, and things get better, that would not be normal, and it would be puzzling why that would happen.
Also, filters don't tend to get clogged quickly, unless algae is involved, whether you can see it or not. One of the first signs of algae is the filter quickly clogging and then going back to working after a backwash.. Of course, this repeats again and again, until you fix the algae problem.
Thanks,
Jim R.
Generally, things get worse as the filter gets dirty...
Something has to happen for things to get better, like backwashing your filter..
If you are not doing anything, and things get better, that would not be normal, and it would be puzzling why that would happen.
Also, filters don't tend to get clogged quickly, unless algae is involved, whether you can see it or not. One of the first signs of algae is the filter quickly clogging and then going back to working after a backwash.. Of course, this repeats again and again, until you fix the algae problem.
Thanks,
Jim R.
The pump software knows the power used for each flow at each speed.
For example, at 3,450 RPM, if the power used is 2,800 watts, the flow is calculated to be about 100 GPM.
This method is not very accurate and it can fluctuate a few GPM over time.
Document the Flow in GPM, Speed, Power and System PSI over time to see if that helps us diagnose the issue.
Thanks JamesW. That's interesting that flow is calculated. Good video too.
The System Pressure is also calculated from the power and speed.
At 3,450 RPM and 2,800 watts, the flow is calculated to be about 100 GPM and the "System Pressure" is calculated to be about 76 feet of head or about 33 psi (76/2.31).
At 3,450 RPM and 2,800 watts, the flow is calculated to be about 100 GPM and the "System Pressure" is calculated to be about 76 feet of head or about 33 psi (76/2.31).
If you have any initial conditions, you can calculate the new conditions at a different speed.
For example if the initial conditions are 100 GPM, 76 feet of head loss (33 psi), 2,800 watts and 3,450 RPM, the new conditions at 1,725 RPM are expected to be about 50 GPM, 19 feet of head loss (8.2 psi) and 350 watts.
www.engineeringtoolbox.com
For example if the initial conditions are 100 GPM, 76 feet of head loss (33 psi), 2,800 watts and 3,450 RPM, the new conditions at 1,725 RPM are expected to be about 50 GPM, 19 feet of head loss (8.2 psi) and 350 watts.
Affinity Laws for Pumps: Principles, Formulas & Calculator
Turbo machines affinity laws can be used to calculate volume capacity, head or power consumption in centrifugal pumps when changing speed or wheel diameters.
www.engineeringtoolbox.com
Given any operating point, you can calculate a System Curve.
Y = (Head Loss/Flow^2)X^2
Example: 76/(100^2) = 0.0076
So, Y = 0.0076X^2.
Y is head loss in feet and X = flow in GPM.
www.wolframalpha.com
___________________________________________________________________________
www.wolframalpha.com
Y = (Head Loss/Flow^2)X^2
Example: 76/(100^2) = 0.0076
So, Y = 0.0076X^2.
Y is head loss in feet and X = flow in GPM.
y = 0.0076X^2, y from 0 to 80 - Wolfram|Alpha
Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.
www.wolframalpha.com
y = 0.0076X^2, y from 0 to 30 - Wolfram|Alpha
Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.
www.wolframalpha.com
Last edited:
I'm still seeing flow fluctuations with no obvious reason for why flow decreases, increases, decreases and continues this cycle. I've back washed and checked and cleaned pump basket and skimmers. Pentair IC60 is still removed from winter. Here's an example of the fluctuations I've recently seen.
3/10/24 7:12pm
Power Usage: 141
RPM; 1320
Flow (GPM): 25
3/11/24 7:11am
Power Usage: 136
RPM; 1320
Flow (GPM): 23
3/11/24 1:26pm
Power Usage: 136
RPM; 1320
Flow (GPM): 24
3/11/24 4:43pm
Power Usage: 138
RPM; 1320
Flow (GPM): 23
3/11/24 8:40pm
Power Usage: 141
RPM; 1320
Flow (GPM): 25
3/11/24 9:17pm
Power Usage: 132
RPM; 1320
Flow (GPM): 21
3/12/24 12:10pm
Power Usage: 136
RPM; 1320
Flow (GPM): 23
3/12/24 6:54pm
Power Usage: 139
RPM; 1320
Flow (GPM): 25
3/13/24 2:28am
Power Usage: 130
RPM; 1320
Flow (GPM): 20
Here is when I manually increased RPM to increase flow rate:
3/13/24 2:47am
Power Usage: 201
RPM; 1540
Flow (GPM): 25
Within a day later the flow rate was 28-29 GPM and I lowered the RPM down again for 25 GPM. Then the cycle repeats itself.
I realize flow rate varies a little and drops over time but my concern is the big swings like 4-5 GPM. And when I put my SWG back in I'll probably have to set the RPM much higher than normal so the SWG flow rate is always satisfied.
Any ideas? Could this be a problem with the motor or the sand filter (mine is filled zeo sand). How can I further troubleshoot or am I overthinking this and just check and adjust RPM often as I'm doing now? This weird operation has only been occurring for maybe 4-6 months or so. I used to be able to set RPM and I would gradually increase it as the filter became dirty until my next backwash.
Thanks.
3/10/24 7:12pm
Power Usage: 141
RPM; 1320
Flow (GPM): 25
3/11/24 7:11am
Power Usage: 136
RPM; 1320
Flow (GPM): 23
3/11/24 1:26pm
Power Usage: 136
RPM; 1320
Flow (GPM): 24
3/11/24 4:43pm
Power Usage: 138
RPM; 1320
Flow (GPM): 23
3/11/24 8:40pm
Power Usage: 141
RPM; 1320
Flow (GPM): 25
3/11/24 9:17pm
Power Usage: 132
RPM; 1320
Flow (GPM): 21
3/12/24 12:10pm
Power Usage: 136
RPM; 1320
Flow (GPM): 23
3/12/24 6:54pm
Power Usage: 139
RPM; 1320
Flow (GPM): 25
3/13/24 2:28am
Power Usage: 130
RPM; 1320
Flow (GPM): 20
Here is when I manually increased RPM to increase flow rate:
3/13/24 2:47am
Power Usage: 201
RPM; 1540
Flow (GPM): 25
Within a day later the flow rate was 28-29 GPM and I lowered the RPM down again for 25 GPM. Then the cycle repeats itself.
I realize flow rate varies a little and drops over time but my concern is the big swings like 4-5 GPM. And when I put my SWG back in I'll probably have to set the RPM much higher than normal so the SWG flow rate is always satisfied.
Any ideas? Could this be a problem with the motor or the sand filter (mine is filled zeo sand). How can I further troubleshoot or am I overthinking this and just check and adjust RPM often as I'm doing now? This weird operation has only been occurring for maybe 4-6 months or so. I used to be able to set RPM and I would gradually increase it as the filter became dirty until my next backwash.
Thanks.
Jim explained it in post #5. "This method is not very accurate and it can fluctuate a few GPM over time." What I saw in your list would not bother me, but I don't have automation that is set to monitor GPM. I just turn my VSF on and it runs it's schedule. Period.
20 GPM is the limit for flow monitoring, so you are right on the line.
I would not worry about it.
I would not worry about it.
dj,
I still do not under this fascination with GPM.. No matter what the GPM reading is, your SWCG will turn on at whatever flow makes it turn on.. It does not matter if the manual says you need 20, 25, or 30 GPM.. The only thing that matters is the particular speed or flow that actually turns on your cell when it is installed in your system.
The best way to find that speed/flow is reduce the flow until the SWCG reports 'low flow'.. Then, slowly increase the flow until the cell just reports good flow. Then add a little more flow and call it a day.
Thanks,
Jim R.
I still do not under this fascination with GPM.. No matter what the GPM reading is, your SWCG will turn on at whatever flow makes it turn on.. It does not matter if the manual says you need 20, 25, or 30 GPM.. The only thing that matters is the particular speed or flow that actually turns on your cell when it is installed in your system.
The best way to find that speed/flow is reduce the flow until the SWCG reports 'low flow'.. Then, slowly increase the flow until the cell just reports good flow. Then add a little more flow and call it a day.
Thanks,
Jim R.
Interesting data concerning flow and operation range. Thanks!
I found this thread diagnosing my issue. I went on vacation, came back to a very green algae ridden pool. I suspected it was algae and kept backwashing and SLAMMing however, the pump RPM would fluctuate like yours.
This is a new pool to me so I am not familiar with the past history. I have 2 skimmers, 1 apparently never catches leaves while the other one is full twice a day (that’s a whole other issue).
Eventually spent some time looking and trying to switch to the skimmer which “wasn’t working” and the pump would surge, lose prime, and would fluctuate all day long. I eventually figured out 1 skimmer is about 2 inches higher than the other and the water was getting low. I don’t have an autofill, so I added water until it was above the second skimmer.
It seems like with both skimmers partially on, there were points in the day where it was sucking air and causing the pump to cavitate and lose prime and the flow rate would fluctuate like you are describing, and I would adjust the RPM.
Again, not sure if this helps but thought I would share since I was just lost trying to figure this out until I got down on my hands and knees to look in the skimmers. I’m no expert, this VSF pump seems to have all sorts of smarts to prevent the loss of prime and a ton of knobs you can turn to adjust its settings (which I did many times) and in the end it was something really something simple.
This is a new pool to me so I am not familiar with the past history. I have 2 skimmers, 1 apparently never catches leaves while the other one is full twice a day (that’s a whole other issue).
Eventually spent some time looking and trying to switch to the skimmer which “wasn’t working” and the pump would surge, lose prime, and would fluctuate all day long. I eventually figured out 1 skimmer is about 2 inches higher than the other and the water was getting low. I don’t have an autofill, so I added water until it was above the second skimmer.
It seems like with both skimmers partially on, there were points in the day where it was sucking air and causing the pump to cavitate and lose prime and the flow rate would fluctuate like you are describing, and I would adjust the RPM.
Again, not sure if this helps but thought I would share since I was just lost trying to figure this out until I got down on my hands and knees to look in the skimmers. I’m no expert, this VSF pump seems to have all sorts of smarts to prevent the loss of prime and a ton of knobs you can turn to adjust its settings (which I did many times) and in the end it was something really something simple.
Thanks vegasbeep. Your symptoms sounds a lot like mine but I don't have a problem with the skimmers sucking air.
Last Sunday I added calcium to the pool and ran the pump at full speed for about 25 minutes. Surprisingly, the flow rate held steady after that for nearly 2 days. Early this morning it dropped from a solid 27 GPM to 21 GPM. I was hoping that somehow running the pump at full speed resolved the problem but no such luck.
Last Sunday I added calcium to the pool and ran the pump at full speed for about 25 minutes. Surprisingly, the flow rate held steady after that for nearly 2 days. Early this morning it dropped from a solid 27 GPM to 21 GPM. I was hoping that somehow running the pump at full speed resolved the problem but no such luck.