IntellifloXF VSF will not pump more than 83 GPM even with low Total Head in 3" pipes

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jcoop1

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Jul 10, 2023
6
Seattle, WA
I am installing a sheer descent style water feature that needs 140 GPM to clear the deck into our pool. I thought I had done all my homework regarding total head calculations and performance curves. Using the Pentair Total Head Calculator, I calculated about 20 feet of head at 140 GPM using a dedicated 3" line and dedicated pump. For reference, I have a two 3" suction lines about 3' deep at the deep end of the pool, joined through a "T" (for safety), that then travel 120 feet through six 90 degree turns and two 45 degree turns and then back again to the water feature through about the same number of turns and distance. The water feature is about 4 feet above the water line, and currently I have the 3" pipe at that elevation just pointing towards the pool for testing with no water feature.

I decided on the IntellifloXF VSF because the performance curves showed it supported higher GPM at lower head ranges (5-20 ft total head) than the IntelloFlo or IntelliFlo3.

xf.png

When I started testing, I'm only getting 83 GPM at 3450 RPM which would equate to 90 ft total head on the graph which is WAY off from my calculation of 20 ft head. I tested at several speeds and got the following
750 RPM - 1 GPM
1500 RPM - 44 GPM
2350 RPM - 64 GPM
3110 RPM - 78 GPM
3450 RPM - 83 GPM

I actually have a second almost identical setup with a second pump for a second water feature and am getting about the same results.

I know that 240 ft of pipe with ~16 turns is a lot, but I thought a dedicated 3" pipe with the IntellifloXF VSF would have no problem getting 140 GPM or over. I'm wondering if something else is going on with "low" Total Head and possibly the pump having too little resistance to get the maximum GPM? The performance curve lines always seem to "end" to the lower right as the head gets lower and I'm wondering how the pump behaves if you go below the total head where they stop the lines.

If my calculations are off, my last resort is to relocate the pumps 10-15 feet from the suction and water feature, but that will be quite costly and difficult.

Also, I am trusting that the GPM reading on the pump is roughly accurate. I've purchased a flow meter but haven't had a chance to install it to confirm the readings.

Any thoughts?
 
Welcome to TFP.

You have no filter in the water flow?

Going to be interesting to see what @mas985 thinks.
 
Based upon your description AND assuming there is no filter, no heater, no valves, etc., then I get about 15' of dynamic head @ 140 GPM + 4' static head or a total of 19' of head which is close to what you got.

So to confirm, there is nothing else that is in the path of the water other than what you have described?

Have you checked the pump's impeller for any blockages?

Another confirmation method would be a pressure/suction measurement in the pump's drain plugs.
 
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Thanks ajw22 for the welcome. I've been lurking for a while trying to figure this out myself, but with no luck.

There are no filters, heaters, valves, or anything else. This plumbing dedicated to running just the waterfall. I actually have two roughly identical plumbing setups with two IntelliFloXF VSF pumps and they are behaving about the same. Just to be clear, I ultimately need 280 GPM (maybe even 300-320 GPM) for the waterfall (it's actually a custom built 10' stainless steel 'sheer descent' style waterfall from Majestic Water Spouts that I'm going to feed with the two 3" pipes at 140 GPM through manifolds that will feed eight 1.5" inlets on the water feature baffle box - The 10' opening is 0.16" high so it needs this high GPM to clear about 2' distance from a height of 2'10" to get into the pool). At this point the water feature is not hooked up and I just have the two systems with the two 3" pipes just pointing back into the pool at about the 4' of height above the water line. A picture helps:
waterfalltest.jpg


I haven't checked the impeller, but these are brand new pumps and both are behaving identically which makes me suspicious it is NOT blockage in the impeller. I am also a novice just trying to learn, so I haven't investigated how I'd even check the impellers myself.

I just saw on another post that their may be a way to see "system psi" on the pumps manual display. I did not see that in the Intellicenter pump menu on the iPhone app which is where I was getting my GPM/RPM measurements. I can look at that.

That said, do you have pointers to how I can check pressure at the pressure/suction drain plugs (pointer to equipment I need and what to do). Also, I bought a Blue-White water flow meter for the 3" pipe but haven't installed. On another thread, I saw some concern about accuracy of those flow meters, and the only place I'm comfortable putting it is on the 1' of pipe just before the pool in the above photo (and that's less than their recommended length of pipe they say is needed for accurate measurements) Any other suggestions for another way to confirm the GPM is what's being read on the pump would be appreciated as well.

Not that this likely matters, but I purchased all my equipment and had the installation done through a good local pool builder, BUT, I had to purchase the IntellifloXF VSF pumps online through ePoolSupply. I only did this because my pool builder said they couldn't get the IntelliFloXF VSF from Pentair directly since they had been discontinued. The pool builder built the plumbing and installed the pumps for me, but I was a bit nervous getting important hardware "online" and being a bit on my own. Had the pool builder been the ones to size and buy the pump, they'd have been responsible for making sure it was getting the required GPM, but since I got the pumps on my own I'm out of luck if it doesn't get the desired flow rate. From the picture, you can see that at ~80 GPM, the water makes it mostly into the pool through the two 3" pipes, but the surface area of 10' by 0.16" (19.2 sq inches) "sheer descent" is less than two 3" schedule 40 PVC pipes (14.54 square inches), so the velocity out of the water feature will be lower and I'm worried it won't clear the deck when installed. The company that built the water feature tested it to need 280 GPM for my scenario.
 
You can remove the drain plugs and install a pressure gauge in the back drain plug and a vacuum gauge in the fromnt drain plug to get the actual pressures.

The thread is 1/4" NPT.

4FLT5_AS02


 
jcoop1 said:
I haven't checked the impeller, but these are brand new pumps and both are behaving identically which makes me suspicious it is NOT blockage in the impeller. I am also a novice just trying to learn, so I haven't investigated how I'd even check the impellers myself.
Click to expand...
You can first look in the pump basket impeller inlet to see if there is any debris stuck in there. But to inspect the impeller directly, you would need to remove the wet end from the motor plate.

jcoop1 said:
That said, do you have pointers to how I can check pressure at the pressure/suction drain plugs (pointer to equipment I need and what to do). Also, I bought a Blue-White water flow meter for the 3" pipe but haven't installed. On another thread, I saw some concern about accuracy of those flow meters, and the only place I'm comfortable putting it is on the 1' of pipe just before the pool in the above photo (and that's less than their recommended length of pipe they say is needed for accurate measurements) Any other suggestions for another way to confirm the GPM is what's being read on the pump would be appreciated as well.
Click to expand...
I would agree with the assessment of the Blu-White flow meter. The check valve variety is much better.

But for a pressure and suction measurement, you can any gauge that has a 1/4" thread. For pressure, a similar pressure gauge that is on the filter.

jcoop1 said:
Not that this likely matters, but I purchased all my equipment and had the installation done through a good local pool builder, BUT, I had to purchase the IntellifloXF VSF pumps online through ePoolSupply. I only did this because my pool builder said they couldn't get the IntelliFloXF VSF from Pentair directly since they had been discontinued. The pool builder built the plumbing and installed the pumps for me, but I was a bit nervous getting important hardware "online" and being a bit on my own. Had the pool builder been the ones to size and buy the pump, they'd have been responsible for making sure it was getting the required GPM, but since I got the pumps on my own I'm out of luck if it doesn't get the desired flow rate. From the picture, you can see that at ~80 GPM, the water makes it mostly into the pool through the two 3" pipes, but the surface area of 10' by 0.16" (19.2 sq inches) "sheer descent" is less than two 3" schedule 40 PVC pipes (14.54 square inches), so the velocity out of the water feature will be lower and I'm worried it won't clear the deck when installed. The company that built the water feature tested it to need 280 GPM for my scenario.
Click to expand...
Do the two pumps have separate suction plumbing?
 
jcoop1 said:
on the iPhone app which is where I was getting my GPM/RPM measurements. I can look at that.
Click to expand...

I do not believe the Intelliflo pumps have any direct measurement of GPM. What you see is a calculated performance number that I would take with a grain of salt and skepticism.

I would look at getting a flow meter like this to directly measure what is going on....

www.flows.com

Pit Rated Paddle Wheel Flow Meter - WM-PT Series

WM-PT Series Plastic Paddle Wheel Flow Meter is a durable, pool water meter. Order Online!
www.flows.com www.flows.com
 
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Ok - I'm getting a "Meanlin Measure" 0-60psi liquid pressure gauge and -30-0 liquid filled vacuum gauge tomorrow from Amazon and will report back. It did not look like there was enough room to install them in the drain plugs, so I got a 45 degree brass elbow.
Pressure gauge
Vacuum gauge
45 degree elbow
Are there better choices than the 45 degree elbow to get the gauge to screw into the drain plugs (e.g. flexible tube)? I couldn't find any.

@mas956 - Yes there are two separate suction plumbings. The back of the pool has four suction pipes - Two go into a T then to the first pump, and the other two go into a separate T to then to the other pump. Here's a picture showing the suction for each pump in red and the returns in green.
pipes.jpg

@ajw22 - Thanks for the pointer to the flow meter. I'm going to try measuring the PSI first but may resort to that.
 

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I'll be careful

I got some "system psi" measurements off one of the pump display itself

1500 RPM - 7 psi - 38 GPM
2350 RPM - 17 psi - 57 GPM
3110 RPM - 31 psi - 70 GPM
3450 RPM - 38 psi - 77 GPM

What is "system psi" and can I use it to estimate total head. Is it supposed to be the same as the pressure at the back drain plug?
 
I have used flex tube before with a 1/4" fitting on the end and that works just fine. It is a little easier to manage where there is not enough clearance.

Also, at full speed, that plumbing should be delivering close to 200 GPM. At that flow rate, water velocity is above 9ft/sec and with a height of 4', the water should shoot out about 4.5' which it appears to be doing. The height and the distance away from the wall are about the same. So just from the visuals, the flow rate looks to be about right.

System PSI is the total head loss so in this case it is close to 88' which does not seem right based upon the other evidence.
Total Head = System PSI * 2.31

From the drain plugs:
Total Head = Return PSI * 2.31 + Suction (in-HG) * 1.13
 
Multiply the system pressure by 2.307 to get total feet of head.

You can then draw a system curve by plotting the head loss at the speed.

psi........Total feet of head

7.............16.15

17...........39.22

31...........71.52

38...........87.7

1500 RPM - 7 psi - 38 GPM

2350 RPM - 17 psi - 57 GPM

3110 RPM - 31 psi - 70 GPM

3450 RPM - 38 psi - 77 GPM

1689113631548.png
 
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Based on the system pressure, the flow rates from the performance curve should be

Speed in RPM................Flow in GPM
1,500.......................................54
2,350.......................................73
3,110.......................................85
3,450.......................................94

The head loss seems excessive for the plumbing, so something is off.

What is the power usage at each speed?

1689114884559.png

1689115194571.png
 
First, thank all of you for your time in responses. I hate asking other people for help, but this has been invaluable.

Second - Some encouraging news. I didn't have a drill bit to properly install the Blue-White flow meter that I had, but I gave it a shot just clamping one side right to where the 3" pipe exits to the pool. To my happy surprise, the flow at 3450 RPM read about 175 GPM on the flow meter:

Flow.jpg
I know that my hacked installation makes the reading unreliable, but my suspicion is that using the meter this way would likely result in a lower reading than accurate, not one that was higher than the true flow. I also understand that this flow meter itself might not be the most accurate, but "hopefully" it is roughly accurate and indicates that the true flow is much higher than the 77 GPM per minute reported by the pump.

@JamesW - Here are the power usages I had recorded
1500 RPM - 7 PSI - 254 W - 38 GPM
2350 RPM - 17 PSI - 899 W - 57 GPM
3110 RPM - 31 PSI - 1990 W - 70 GPM
3450 RPM - 38 PSI - 2770 W - 82 GPM

The 3450 RPM is a new reading I took which was slightly higher GPM than earlier.

It looks like this "roughly" matches your calculations for 3450 RPM, the performance curves, and power curve (it's at least in the ballpark).

38 PSI is "almost" 90 ft head so 82 GPM is reasonable at 3450 RPM according to the performance curves, and so is 2770 W at 82 GPM according to the power curve at 3450 RPM.

This makes me suspect that the pump is calculating GPM based on its reading of "system PSI" and probably its own understanding of its power curve and/or performance curve.

HOWEVER - The "38 system PSI" readings and "82 GPM @ 3450 RPM" that I got do not make sense with two other facts
#1 - The calculations for my plumbing at 82 GPM show it should be just under 10 ft of head, not 87 ft indicated by the 38 system PSI.
#2 - The blue-white flow meter was showing 175 GPM

If we assume the 175 GPM is true, my head calculations for my plumbing are about 28 ft. That seems plausible at 3450 RPM. If the GPM is actually around 200, the head would be 35 ft and match perfectly with the performance curve (35 ft, 3450 RPM, 200 GPM). This aligns with everything @mas985 said about the waterflow looking like it could be 200 GPM and that the pump should be producing that amount given my plumbing.

Let's say it's really getting 200 GPM at 35 ft of head - This would mean the "system PSI" should have been 35/2.307 or 15.2 instead of 38. Is it possible that whatever is measuring "system PSI" is really off that much, and that is what's throwing off the pumps internal calculations of GPM?

Tomorrow I'll get the pressure/vacuum meter and hopefully have a better insight into whether the root cause of the pump reporting unexpectedly low GPM is its poor measurement of "system PSI".
 
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If the Intelliflo XF is displaying incorrect flow rate, it is likely that the wattage is also incorrect since that is what is used to determine the flow rate.

I have a spreadsheet in my signature that simulates this same calculation from RPM & Watts to GPM and it estimates about 86 GPM which is very close to what that Intelliflo XF reports. So this part is at least consistent.

However, what if the wattage is also wrong?

But again, if you do the head calcs for the pipe and fitting and overlay that with the pump's head curve, it comes up close to 200 GPM and also matches what Newton would estimate:

waterfalltest-jpg.512557
 
They can measure the voltage and amperage or the power with a power meter.

Measuring the power with a wattmeter would be more accurate.

The pressure measurements will hopefully help.

Maybe install the flow meter correctly to make sure that it is reading accurately.

We also do not know if the power is being measured at the 240 volts single phase input to the drive or at the 3 phase power out of the drive.

Ideally, you would measure the power at both places and measure the power factor.

Measuring the power from the drive to the motor would require a wire connector that would allow a three-phase power meter to be installed.

If the power is being measured at the drive output to the motor, then they might only be measuring one leg (of 3) and not all three legs, which is accurate unless the legs are not equal.
 
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I had one more idea that came to me while walking the dog.

Maybe there is more than one solution for the measured power and the drive just takes the one that is closest to the left.

The BEP for the Intelliflo XF is around 145 GPM. For most pumps, to the right of the BEP point the watts vs GPM flattens and sometimes oscillates. So if the flow rate of 200 GPM is correct, perhaps the wattage of 2770 watts is also correct. There are just multiple solutions.

You can see this in the standard Intelliflo power curve. To the right, the power curve becomes non-linear and there are locations where there are two flow rates for the same wattage. So the XF could be similar.

1689176131425.png
 
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