Calculated Flow Rate

Dave_NJ

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Aug 15, 2019
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I like investigating/poking around with things and started looking into the flow rate for my pool equipment. I understand flow rate isn't all that important but I'm curious nonetheless.

Is there a reason behind the recommended flow rate charts? I've seen the 8 fps/10 fps charts and the corresponding flow rates, just curious why this is the standard.

I hooked up a vacuum gauge to the pump suction drain port and installed the nifty filter pressure gauge from TfTests (it's a nice gauge btw!).

I tested my pump (CircuPool 3hp VS) at three different speeds (3000, 2500 and 1500 rpm) and this is what I got:

3000 rpm
Vacuum -8.25 Hg
Pressure 13.5 psi

-8.25 x 1.13 = 9.3225
13.5 x 2.31 = 31.185
Total 40.5075
90 gpm?

2500 rpm
Vacuum -6 Hg
Pressure 9 psi

-6 x 1.13 = 6.78
9 x 2.31 = 20.79
Total = 27.57
70 gpm?

1500 rpm
Vacuum -2.5 Hg
Pressure 2.25 psi

-2.5 x 1.13 = 2.825
2.25 x 2.31 = 5.1975
Total = 8.0225
45 gpm?

Here is the relevant performance curve from CircuPool:

202006271801023321449792270ce4fe3.png

Based on the 8 fps/10 fps chart (for 1.5" piping that equals 50 gpm/62 gpm) it seems like 1500 rpm is slower than recommended and 2500 rpm is too fast. Should I care enough to adjust my pump speed/schedule to try and get close to the recommended flow rate or does it really not matter?
 
Last edited:

mas985

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I am not sure where you got the 8 fps and 10 fps "recommendations" but those are much too high. Current regulations stipulate UPPER LIMITS for velocity of 6 fps for suction side plumbing and 8 fps for pressure side plumbing. But it is important to understand those are upper limits, not targets. Lower velocity in plumbing is always better for efficiency and filtering so you should always be targeting the lowest flow rate to meet the required task whatever that may be.

For more information, please see the Hydraulics 101 sticky in my signature.
 
Last edited:

mas985

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Unfortunately, many sites on the internet contain false or inaccurate information. Inyo is not an exception.
 

Dave_NJ

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Aug 15, 2019
108
North NJ
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Unfortunately, many sites on the internet contain false or inaccurate information. Inyo is not an exception.

The internet may have inaccurate information?! I'm shocked! ;)
 

Dave_NJ

Silver Supporter
Aug 15, 2019
108
North NJ
Pool Size
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Chlorine
Salt Water Generator
SWG Type
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Those were interesting, thanks for sharing. So the rational behind the new regulations and flow rates is better energy efficiency.

I was curious if it had to do with better ways to filter/clean pools but that doesn't appear to be the case. I guess the slower water speeds will naturally lend to more efficient filtering as well since the debris is more likely to be trapped in the filter rather than pushed through.

It's also interesting they are referencing pool turnover rates (one turnover every 6 hours) as a criteria that needs to be met with flow rates. My understanding is turnover rates aren't all that important but I'm new to all of this.
 

mas985

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Both energy efficiency and VGBA compliance for velocity at the MD grate.

Actually, the article specifies a maximum turnover rate, not a minimum turnover rate that you will see on many sites. So what we teach here is that there really is no minimum flow rate or turnover. Often times you will see a minimum turnover of 1 or 2 per day. This is the myth that we often reference.

However, the standard also says that the hydraulic system must be designed for a turnover rate no faster than six hours, thus slowing the water down.
 
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Dave_NJ

Silver Supporter
Aug 15, 2019
108
North NJ
Pool Size
24000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-60 Plus
Both energy efficiency and VGBA compliance for velocity at the MD grate.

Actually, the article specifies a maximum turnover rate, not a minimum turnover rate that you will see on many sites. So what we teach here is that there really is no minimum flow rate or turnover. Often times you will see a minimum turnover of 1 or 2 per day. This is the myth that we often reference.

Great explanation, thank you
 

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