1. ## Calculating GPM

I have been reading through some rather involved threads and trying to sort out a good estimate for GPM at various speeds. I used the spreadsheet that Mark posted in the 101 thread an got some confusing results below RPMs lower that 1700. I was hoping that someone can help me sort out a ballpark. Here is what I have:

Intelliflo VS+SRVS
2.5 suction with 2 independent skimmer runs and one main run
2.0 return split at pool into four return ports
MT400K BTU Heater

RPM 1500 - Watts 205 - PSI 2.5
RPM 2350 - Watts 818 - PSI 10

The spreadsheet says I have ~ 7 GPM @ 1500 and ~52 GPM @ 2400

Thanks in advance for any help!

2. ## Re: Calculating GPM

Do you happen to have a check valve in your plumbing and if so, do know if it is the swing type or the axial spring type?

One thing that can really slow down flow rates at low RPM are check valves. 2/2.5" plumbing should have fairly low head loss and yield something close to the following results from Curve-C:

2350 RPM, 66 GPM @ 36' of head and 911 watts
1500 RPM, 45 GPM @ 17' of head and 339 watts

Your numbers at 2350 RPM seem to be closer to Curve-A which represents long runs of 1.5" plumbing and at 1500 RPM, your plumbing seems to be 5x worse than Curve-B which is really bad. So my first thought is that a check valve is closing under lower flow rates and increasing the head loss. Others with check valves have experienced this same issue.

3. ## Re: Calculating GPM

Not sure on the valve. Not even sure what to look for. Where would that valve be and what might it look like?

Also, could the check valve be causing flow issues at 2350 RPM?

4. ## Re: Calculating GPM

I think this might be it. The black valve with the clear top on it on the return, but that is on the return for the spa and I believe it is to prevent the raised spa from siphoning out when it is not in use. It is a Pentair valve.

5. ## Re: Calculating GPM

Dear Mr pool builder?

6. ## Re: Calculating GPM

That looks like a check valve. I had the same issues. Mark replotted my curve using the good numbers to extrapolate what thr bottom numbers could be. I still need to open up my check valve and take out the spring.

7. ## Re: Calculating GPM

Originally Posted by racket
Dear Mr pool builder?

8. ## Re: Calculating GPM

Update - the check valve is definitely on the spa return. It should not be impacting the flow for pool. Any other ideas on what might be causing my flow to be this low?

I do hear what sounds like water rushing at the heater at lower speeds. Could that be cavitation?

9. ## Re: Calculating GPM

The vs+svrs pump should have came with a vacuum gauge. What does that read?

10. ## Re: Calculating GPM

if it came with one, it is not installed. I could get one and hook it up to the pump and see. If I get a vacuum reading will it help sort out if the issue is on the suction side vs return side?

11. ## Re: Calculating GPM

You can get a good estimate of total head loss with both the filter pressure and a vacuum measurement.

Besides a check valve, one other thing that can throw the spreadsheet estimates off is a partially clogged impeller. Was the pool recently opened?

12. ## Re: Calculating GPM

Originally Posted by loweran
if it came with one, it is not installed. I could get one and hook it up to the pump and see. If I get a vacuum reading will it help sort out if the issue is on the suction side vs return side?
If you believe it may be cavitating it will lead you to the source.

13. ## Re: Calculating GPM

starting to think the source might be the Ozonator that is plumbed into the suction port at the bottom of the basket. Anyone had issues like this before? There is a checkvalve that screws into the plug port and is plumbed with a compression fitting to a tube. It runs to the ozonator. There is also a flow valve at the ozonator that has a ball to adjust the flow. The darn thing bounces wildly which makes it difficult to adjust.

14. ## Re: Calculating GPM

Ozonators tend to add quite a bit of air to the plumbing which can affect the flow characteristics of the pump. Try closing off the air flow and see if the wattage changes much.

15. ## Re: Calculating GPM

I will give that a shot this evening.

16. ## Update

no difference with the flow turned off. I do hear a difference in the pump at higher speeds when I open it up. I don't have any bubbles visible in the pump basket. Guessing I should have the PB plumb it after the pump. Don't know how successful I will be at convincing them of that.

This is kind of frustrating. I bought the Intelliflo to save me \$s on electric usage and now I am having to run the pump in the 1900 rpm range or above to get a turnover in 12 hours.

17. ## Re: Calculating GPM

Originally Posted by mas985
You can get a good estimate of total head loss with both the filter pressure and a vacuum measurement.

Besides a check valve, one other thing that can throw the spreadsheet estimates off is a partially clogged impeller. Was the pool recently opened?
Pool was just started new. I will discuss this with the PB.

18. ## more data

When I ramp the pump up to max, I get visible bubbles shooting out from the two returns closest to the pump. At 2500 or so I do not see those. I tried closing the ozone flow but it made no difference.

I checked the impeller and it was clear and moved easily. I do not think the lines are clogged as I have good suction from all three suction lines.

I emailed my PB today and explained my situation. I hope he can address the issue.

I appreciate all of your input as it will help me discuss thoughts with the builder. I am much more educated than before. Thanks and keep the ideas coming.

19. ## update

There is a check valve that the ozonator connects to at the pump volute. It is not allowing me to measure my suction properly. I hooked up a guage to it and it got a reading of 8 in @ 3450 RPM. I am going to have to get a fitting hook up the vacuum gauge properly. I did rule out the ozonator as I put the plug in the pump and ran it. It gave me the same numbers. That heater sure does make a lot of noise at lower RPMs. Sounds like water rushing.

If I cut off a skimmer, or both skimmers, would I expect to see a difference in the wattage consumed? Wonder if I can get a differential on the skimmers to see if one of them is clogged.

Thoughts?

20. ## Re: Calculating GPM

If you shut off only one of the suction lines, you may not see much of a change in either a vacuum measurement or a wattage measurement. However, if you shut off two of the three lines, I would expect to see a change in watts, vacuum and pressure. To make sure all three lines are clear, turn on each line one at a time while shutting off the others. When you do this, record filter pressure and if possible vacuum for each of the three lines and all three on together. I can then confirm the flow rate and your plumbing curve.

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