Measuring flow at the returns

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carlscan26

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Dec 22, 2010
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In looking at flow meters the requirements for an accurate reading for the Blue-White meters are that you have straight pipe for 10X the diameter of the pipe before the meter and 4X after it. For 2" pipe that's 28" of straight pipe which I don't have anywhere on my pad. Which got me to thinking - what if I measured at each of my returns and summed the results?

I am imagining a setup with a hose that attaches to the return port and gently curves to a straight section of same sized pipe of proper length with the flowmeter on it and then a hose back into the pool.

I'm assuming that the rig and the rise in elevation to deck height (about 15-18") would not create a significant enough back pressure to affect the individual return port's flow which I may be wrong about...

I'd love some feedback from the experts on here :)
 
It would be simpler to add a section of straight pipe to your equipment pad than it would be to use the rig you are talking about. Also, the extra hose length and the vertical rise will both affect the flow rate. Usually changing the plumbing around to get some straight pipe is very simple, though it often takes twice the length the meter requires.
 
JasonLion said:
It would be simpler to add a section of straight pipe to your equipment pad than it would be to use the rig you are talking about. Also, the extra hose length and the vertical rise will both affect the flow rate. Usually changing the plumbing around to get some straight pipe is very simple, though it often takes twice the length the meter requires.
Click to expand...

I wish I could, but my setup is pretty tight
 
If you post a picture I can suggest something. Usually you only need about five inches of pipe to patch into. One good approach that works almost everywhere is to run a new section of pipe vertically and then back down again.
 
Twice the length because you need to go up and then down again, so twice the length required by the flow meter of additional pipe compared to what you had originally, but only about 2' added vertically.
 
Ok good. I thought you meant the run where thr meter is could need to be twice what they had in the instructions.

On a different thought; I'm not finding a flow meter that reads below 20 gpm...does anyone know of one? I was hoping to get as low as 10. The only thing I've found that claimed a wide range from very low to very high used a calorimetric sensor and you have to call to discuss pricing - they seem very industrial application oriented and I'm betting it has a corresponding price tag.
 
Blue-White makes low range and high range meters for both 1.5" and 2" pipe. For 1.5" the ranges are 9-30 GPM or 20-100 GPM. For 2" the ranges are 15-70 GPM and 40-150 GPM. If low flow rates are important in your situation, you could use the low range 1.5" pipe version. A short section of 1.5" pipe wouldn't make too much difference at low flow rates, though it would have a small effect at higher flow rates.
 

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Keep in mind that the accuracy of a flow rate meter (F300 series) is about 10% of full scale. So the 20-100 GPM is 10 GPM even at a 20 GPM measurement. So they really lose at lot of accuracy at the lower ranges. Also, they work by pressure differential so if there is any turbulence in the water stream, that adds to the inaccuracies so installation quality is critical.

It seems you are going to a lot of trouble to measure flow rates and I was just curious as to why? Are you trying to get to a specific turnover? Filter time is a function of a lot of variables and turnover recommendations are simply guidelines. You might be better off just setting up a schedule and speed and see if it is enough to keep the pool clean. If efficiency is your target, the Intelliflo efficiency peaks at around 900 RPM for 1.5" plumbing.

Instead of targeting a turnover, I would approach the problem this way. Use 900 RPM for your general circulation. Set a higher speed such that the skimming and/or a cleaner works properly. Set the skimming time based upon your experience with how long it takes to keep the surface clean. Set the low speed time based upon duration sunlight on the pool to keep the water circulation and properly chlorinated. See how things go and adjust from there.
 
My interest in knowing the flow rate is part perfectionism and part new hobby induced curiosity. I do a good bit of number crunching in my work and I enjoy this stuff - and yes, I recognize there may be something wrong with me :) That being said, reason does set in and I'm not going to spend hundreds of dollars on what is essentially an optimization exercise. You are right: Optimum efficiency is my goal. We are in a new house to us and the power bills for the first three months are way more than our previous experience or expectations. Since there are so many loads it's impossible to determine exactly how much was due to the old pool pump. So I'm trying to get a good estimate for how much of our bill is the pool with the new equipment. I've built a model for estimating monthly power costs but one of the critical inputs is the power usage for the different run speeds.

I appreciate yours and everyone elses advice and suggestions. I hope I'm not using up your patience?

Thanks for confirming the 900 rpm efficiency point; I came to the same speed with my crunching of the numbers.
 
I completely understand. That is how I started out.

Anyway, I do have another spreadsheet in the Pump Modeling Tools link in my signature which does lifetime cost comparison between pumps. There are a limited number of pumps that have data but if your old pump is not listed, there is another with similar performance. From the data you posted on the other thread, your need to set the plumbing curve to Curve-C with a Plumbing Curve Adjustment setting of 145%. This should get you pretty close to estimating the cost savings.
 
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