Looking for a way to test GPM at each return

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sorpasorpa

In The Industry
May 16, 2024
10
Grand Rapids, MI
TLDR: I'm looking for the most practical way to test GPM at each return.

I work for a pool company and I'd like to be able to test GPM on pools I visit without installing a permanent flow meter in the system. I want to know the GPM so I can calculate filter turn over at different pump RPMs.

For pools with a salt cell, I replace the cell with a flow meter installed on a short chunk of PVC that threads into the salt cell hubs. That works pretty good but I'm looking for a set up that works on any pool. That's why I'm looking for something that threads into the returns since all pools have the same threaded return fittings. I figure I could screw in a device at each return, do my test, and then add up the total GPM of each device.

I was initially thinking the device would be threaded fitting, to a union, 90 up out of the water, 90 to horizontal, and then a flow meter. The flow meter I've been using is not very sensitive under 10 GPM so I'm concerned that I wont really get a reading at each device at lower RPM. On a pool with 5 returns the GPM on each return is going to be very small.

A secondary benefit to this set up is it would allow me to see if there are discrepancies in GPM amongst the returns.

What are your thoughts? Is there a simpler way to achieve what I'm looking for? Should I build the devices? Thanks
 
Welcome to the forum

Turnover is meaningless in a pool. You run the pump for a reason, not to just ‘turnover’ the pool volume.
Read Turnover of Pool Water - Further Reading

I know of no device to achieve your objective without adding back pressure to that return and thus disrupting your test.
 
PoolStored said:
We really don’t use turnover at TFP. We run our pumps for a reason, like heating, filtering, chemical additions, skimming etc.

Great read:

Turnover of Pool Water - Further Reading

www.troublefreepool.com www.troublefreepool.com
Click to expand...
Ok, forget I said turnover. What metric do you use to measure filtering? For heating it's temp, for chemicals it's test kits. I read that article and it basically says filtering is good but don't do it too much if you want to be energy efficient.
 
Owner delight.
If the pool is sanitized and clear (proper chemical balance) the pool owner is delighted. This is TFP Clear. Link-->How Clear is TFP Clear?
If the pool is clear of particulates, then you are filtering enough and the pool owner is delighted.
If the pool is warm enough, then the pool owner is delighted.
If the pool is skimmed enough for the pool owner, the pool owner is delighted.
If the pump runs the water features to the owners satisfaction, the pool owner is delighted.
If the pump uses a vacuum, or suction side pump, and clears the pool to the owners satisfaction, the pool owner is delighted.
If the pump runs on low speed and sanitizes, filters, heats and skims, runs water features, and clears debris on the bottom, and does it at low energy cost, the pool owner is delighted.
 
PoolStored said:
Owner delight.
If the pool is sanitized and clear (proper chemical balance) the pool owner is delighted. This is TFP Clear. Link-->How Clear is TFP Clear?
If the pool is clear of particulates, then you are filtering enough and the pool owner is delighted.
If the pool is warm enough, then the pool owner is delighted.
If the pool is skimmed enough for the pool owner, the pool owner is delighted.
If the pump runs the water features to the owners satisfaction, the pool owner is delighted.
If the pump uses a vacuum, or suction side pump, and clears the pool to the owners satisfaction, the pool owner is delighted.
If the pump runs on low speed and sanitizes, filters, heats and skims, runs water features, and clears debris on the bottom, and does it at low energy cost, the pool owner is delighted.
Click to expand...
Is this a poem? A haiku? Or set to a beat?
 
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Unless it is a commercial pool, it is not too important to measure flow.

Some pumps like Intelliflo have built in flow readings.

You can use the pump performance curves and filter pressure and suction pressure to figure out flow.

You can always add a flowmeter on any pool where you want to know the flow.
 
ajw22 said:
Water clarity.

This is TFP Clear. Link-->How Clear is TFP Clear?
Click to expand...
Is there a scale or method to measuring water clarity? I assume TFB is on board with using precision chemical testing for water balancing so I'm confused why we wouldn't for other aspects of the pool. I'm getting the vibe that it is taboo to want to measure water filtering to any sort of baseline or standard.
 

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JamesW said:
Unless it is a commercial pool, it is not too important to measure flow.

Some pumps like Intelliflo have built in flow readings.

You can use the pump performance curves and filter pressure and suction pressure to figure out flow.

You can always add a flowmeter on any pool where you want to know the flow.
Click to expand...
Could you elaborate how you would calculate flow with pump performance and filter pressure?

I could add a flow meter to every pool we service but I'm trying to develop a modular system to save cost.
 
sorpasorpa said:
I'm getting the vibe that it is taboo to want to measure water filtering to any sort of baseline or standard.
Click to expand...
We do have a standard.

Toss a quarter into the pool. Can you tell if it is heads or tails?

Sometimes analog measurements are the best.
 
The scale is your eyes. If you can see the bottom and read the writing on the drain cover, if the water is crystal clear, if there is no signs of algae and if the test results are balanced then its all good. We monitor filter pressure and clean them when the high flow pressure is 25% above the clean filter pressure and we keep our weir doors in place and the water level 1/2 way up the skimmer mouth. We keep the FC at the top of the scale based on the CYA level. With all of that the pool is fine and flow rates don't matter. I think you are trying to do too much work to prove something to a customer.
 
sorpasorpa said:
Ok, using this method would you limit your pump's run time or shut if off all together if you can see the quarter?
Click to expand...

No, since I run my pump for other reasons then filtering.

sorpasorpa said:
And if you can't see it do you keep increasing the schedule indefinitely?
Click to expand...

I would like to check the water chemistry.

sorpasorpa said:
What if you can never see the quarter no matter how long you run your pump?
Click to expand...
It is a water chemistry or an internal filter problem.

DE filters, cartridge filters, and sand filters all have quirks and must be handled differently for water clarity.
 
TinFoilHat said:
With all of that the pool is fine and flow rates don't matter. I think you are trying to do too much work to prove something to a customer.
Click to expand...
I'm trying to optimize a pump schedules tailored to each pool. This has nothing to do with proving anything. Do you think it's a bad idea to try to optimize a pool systems efficiency?
ajw22 said:
No, since I run my pump for other reasons then filtering.

I would like to check the water chemistry.

It is a water chemistry or an internal filter problem.

DE filters, cartridge filters, and sand filters all have quirks and must be handled differently for water clarity.
Click to expand...
This hypothetically assumes water chemistry is balanced. You are ignoring filter schedule as a variable for some reason. My point is that with your binary quart test there is a huge range of pump schedules in which you can see the quarter. How would you advise me if I asked you for a pump schedule that allows me to see the quarter and run my pump for as little as possible.
 
sorpasorpa said:
Could you elaborate how you would calculate flow with pump performance and filter pressure?
Click to expand...
Get the filter pressure and suction and convert to feet of head.

For example a filter pressure of 29 psi is 29 x 2.31 = 67 feet of head loss.

You can use a vacuum gauge on the suction.

You can estimate the suction head based on (Estimated) flow and pipe size.

For example, if the suction is 100 feet (equivalent) of 2" PVC pipe and the flow is about 50 GPM, then the head loss is about 4.2 feet.

If the flow is 100 gpm and you have (2) 2" PVC pipes and each carries about 50 gpm, the head loss is still about 4.2 feet because each pipe head loss is equal and you only look at one pipe for head loss.

In this example, we have 71 feet of head at full speed (3,450 rpm), so we can find the flow is about 100 GPM.

This puts the System Curve at about "C".



1746204769934.png


www.pentair.com

IntelliFlo3® Variable Speed & Flow Pool Pump

The award-winning, energy-efficient IntelliFlo3 VSF Pool Pump has a quiet design with sensorless flow control, app connectivity, and automation capability.
www.pentair.com www.pentair.com

1746205158805.png


1746205546038.png

This shows different system curves on a pump curve.

System Curve A is a typical curve, B is a poorly designed system and C is a well designed system

As you can see, a system curve like C is much more efficient because it allows for a slower pump speed to achieve a specific flow, which means less power and total energy costs over the pool lifetime.

How to Read Pump & System Curves

1746205583835.png

1746205640733.png
 
JamesW said:
Get the filter pressure and suction and convert to feet of head.

For example a filter pressure of 29 psi is 29 x 2.31 = 67 feet of head loss.

You can use a vacuum gauge on the suction.

You can estimate the suction head based on (Estimated) flow and pipe size.

For example, if the suction is 100 feet (equivalent) of 2" PVC pipe and the flow is about 50 GPM, then the head loss is about 4.2 feet.

If the flow is 100 gpm and you have (2) 2" PVC pipes and each carries about 50 gpm, the head loss is still about 4.2 feet because each pipe head loss is equal and you only look at one pipe for head loss.

In this example, we have 71 feet of head at full speed (3,450 rpm), so we can find the flow is about 100 GPM.

This puts the System Curve at about "C".



View attachment 642409


www.pentair.com

IntelliFlo3® Variable Speed & Flow Pool Pump

The award-winning, energy-efficient IntelliFlo3 VSF Pool Pump has a quiet design with sensorless flow control, app connectivity, and automation capability.
www.pentair.com www.pentair.com

View attachment 642415


View attachment 642416

This shows different system curves on a pump curve.

System Curve A is a typical curve, B is a poorly designed system and C is a well designed system

As you can see, a system curve like C is much more efficient because it allows for a slower pump speed to achieve a specific flow, which means less power and total energy costs over the pool lifetime.

How to Read Pump & System Curves

View attachment 642418

View attachment 642419
Click to expand...
This is interesting to me, thank you!
 
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Reactions: JamesW
sorpasorpa said:
This hypothetically assumes water chemistry is balanced. You are ignoring filter schedule as a variable for some reason. My point is that with your binary quart test there is a huge range of pump schedules in which you can see the quarter. How would you advise me if I asked you for a pump schedule that allows me to see the quarter and run my pump for as little as possible.
Click to expand...
OK, so now you are moving your questioning to pump runtime schedules.

You run your pump for a reason. Other reasons for running your pump longer cover the filtering time needs.

Pump Basics - Further Reading

www.troublefreepool.com www.troublefreepool.com

Consider both speed and duration if you have a VS pump and automation. Reasons for running the pump can be:
  • Mix chemicals: Low speed for 1/2 hour is fine for chlorine and acid additions. Salt, calcium, and stabilizer can require more circulation at higher speeds.
  • SWG: Clean filter flow off speed + 200RPM, for whatever duration you need for the % output of the SWG.
  • Filter: Low speed is better for filtering. Filter long enough so you are happy with the water.
  • Skim: Run the lowest speed that get you sufficient skimming. Run for long enough to get the results you want.
  • Heater: Run at the speed that gives you enough flow for the heater and run for the duration you need to heat.
  • Vacuum: sufficient RPM to operate the vacuum for as long as necessary to clean satisfactorily.
Some of us with VS pumps and a SWG like to run our pump 24/7 at low speed and always add some chlorine to the water.

If you have an In Floor Cleaning Systems, your pump must run much longer at higher speeds.
 

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