Why No Flow Rate?

CaliViking

New member
May 3, 2022
2
Orange County, CA
Moved from old thread HERE

Please help me understand why there is no need to know the flow rate.
If I have a 20,000 gallon pool and can run the pump 20 hours a day (when electricity is cheaper and solar is on). If I assume one turn per day (it is residential with a pool cover and no debris from trees), wouldn't I need 20,000/(20 hours*60 minutes/hour) = 16.7 GPM?
I would have thought that the flow rate is the most important factor, as it determines how much water is filtered per unit time.
I also thought that flow rate would be directly proportional to pump speed (it is a volumetric movement of water).https://www.engineersedge.com/fluid_flow/pump_laws.htm#:~:text=These%20laws%20state%20that%20the,cube%20of%20the%20pump%20speed.
 
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PoolStored

Gold Supporter
TFP Guide
Jun 24, 2021
2,449
Ashtabula, OH
Pool Size
30000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-60
Heaters and SWGs have minimum flow rates that you need to stay above in order for them to stay operating. Both have flow switches. If they don't turn on, there is not enough flow.

Aside from that, turnover is a bit of a myth. Good thread here:
 

Jimrahbe

Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
26,565
Bedford, TX
C,

The idea that you have to "turnover" x amount of water per day to prevent algae is just a myth and just not true. Chemicals (FC and CYA) keep your pool clear and sanitized, not the number of times water passes through the filter. Your filter is just there to capture all the junk that falls into your pool and floats. By the time that your filter captures algae, you have already lost the algae war. No matter how many times your water passes through your filter, it will not prevent you from getting algae.

That said, we don't care if you want to turnover your water 100 times a day, or .1 times a day, it is up to you how you want to run your pool. We just want you to know that turnovers are not a requirement for well-run pool.

You do need to run your pump long enough to produce the chlorine your pool needs, if you are using chlorine tablets, or have a Saltwater Chlorine Generator. If you are using Liquid chlorine, then a couple of hours a day is plenty.

Another reason to run the pump is for skimming. The time to skim the pool really depends on the user and the location. If you get a lot of debris in your pool, then you might have to run the pump longer than someone who gets few debris.

I personally run my pump 24/7 at about 1200 RPM most of the time. I do this because I have a SWCG and like making a little chlorine all the time and I like skimming all the time. I have no idea what my turnover rate is because I run my pump for a reason, and not to meet some mythical number.

Thanks,

Jim R.
 

CaliViking

New member
May 3, 2022
2
Orange County, CA
Moved from old thread HERE

Please help me understand why there is no need to know the flow rate.
If I have a 20,000 gallon pool and can run the pump 20 hours a day (when electricity is cheaper and solar is on). If I assume one turn per day (it is residential with a pool cover and no debris from trees), wouldn't I need 20,000/(20 hours*60 minutes/hour) = 16.7 GPM?
I would have thought that the flow rate is the most important factor, as it determines how much water is filtered per unit time.
I also thought that flow rate would be directly proportional to pump speed (it is a volumetric movement of water).https://www.engineersedge.com/fluid_flow/pump_laws.htm#:~:text=These%20laws%20state%20that%20the,cube%20of%20the%20pump%20speed.
This post was incorrectly moved from "Jandy ePump 2.0 flow rate" to no-flow. The post is not about not having flow, it is about setting the correct flow rate. It looks like the flow rate of the Jandy ePump is the speed of the pump divided by 20 to get gallons per minute. See https://www.jandy.com/-/media/zodia...6228.pdf?rev=3c1a030c0e1049d8970121e08ca6036c - a speed of 600 rpm gives a flow rate of 30 gpm. The relationship between the flow rate and the speed should be linear.
As a side note: I do not believe that it makes any sense to talk about "Feet of Head" for variable speed pumps. If the pump manages to achieve it's speed, then it will manage to create the flow rate. The pump will just consume more current (therefore power) if the resistance in the tubes and the lift is high. "Feet of Head" was probably a good rule of thumb for fixed speed pumps, but not for variable speed pumps.
 

1poolman1

In The Industry
Jul 14, 2014
2,349
Sacramento
Completely block flow with a valve, a "dead head" condition. Pump will continue to spin and move zero water. Allow a filter to get very dirty, increasing the head on the system, the pump will continue to spin and move less water for the same rpm. Real-world experience. Regardless the speed of the impeller, "head" will always affect flow.
 
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