Maximum GPM on mixed sized piping

AviatorBimmer

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Just curious... My pool's piping from the pool to the pad and from the pad to the pool is 1 1/2". Everything above ground at the pad is 2", which includes pump's intake, through the filter, past the SWG and up to the 3-way valve that goes to the pool's returns.

I know 1 1/2" piping has a max flow rate of ~45 GPM while 2" max flow rate is ~75 GPM.

Should I not exceed 45 GPM on my system or am I safe to go up to 75 GPM?
 
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ajw22

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Why do you think your pool needs to run at more then 45 gpm?

Nothing is going to blow up if you run your pump up to 75 gpm. It will be ineffecient and your pump will self limit by the suction intake limits.
 

AviatorBimmer

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Why do you think your pool needs to run at more then 45 gpm?

Nothing is going to blow up if you run your pump up to 75 gpm. It will be ineffecient and your pump will self limit by the suction intake limits.

I'm just trying to figure out what's the fastest and safest flow rate I can run my pump at so I can turnover the entire pool capacity once a day in the shortest amount of time as it's HIGHLY recommended here at TFP.

I'm currently running my pump 24 hours a day at 1000 RPM which gives me 27 GPM and about 2.7 turnover rate.

So you are saying running it at anything over 45 GPM will start to be inefficient because of the limitation imposed by the 1 1/2" piping?

If that's the case, that's exactly what I needed to confirm.

In my case, I can run it at 45 GPM and have it turnover the entire pool volume once in a little over 5 hours.
 

mknauss

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so I can turnover the entire pool capacity once a day
Turnover is a myth. Run your pump to perform a process. Be it generate chlorine with a SWCG, Skim, etc.

Chemistry keeps your water clean and sanitary. The filter captures stuff that falls into the pool.
 

JamesW

TFP Expert
Mar 2, 2011
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I'm just trying to figure out what's the fastest and safest flow rate I can run my pump at so I can turnover the entire pool capacity once a day in the shortest amount of time as it's HIGHLY recommended here at TFP.
What recommendations are you talking about?

The best way to run the pump is as slowly as possible while still achieving the purpose of creating flow.

Purposes include skimming or making chlorine.

Filtering matters, but there's no reason to turn over the pool in a day.
 

AviatorBimmer

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Turnover is a myth. Run your pump to perform a process. Be it generate chlorine with a SWCG, Skim, etc.

Chemistry keeps your water clean and sanitary. The filter captures stuff that falls into the pool.

I see what you are saying but if we want our filter to capture stuff that falls into the pool, doesn't it have to filter all the water to get it out? I don't see how the filter can get stuff out if it doesn't get to it in the first place.

If I can run my pump for 5 hours a day at 45 GPM and fine tune the SWG to be able to generate as much chlorine as needed while filtering the entire volume once, I'm one happy camper. With this setup, I'll use just about 870 watts PER DAY (5 hours total usage). That's about $3.5 a month.
 

AviatorBimmer

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Mar 29, 2021
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Florida
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What recommendations are you talking about?

The best way to run the pump is as slowly as possible while still achieving the purpose of creating flow.

Purposes include skimming or making chlorine.

Filtering matters, but there's no reason to turn over the pool in a day.

So you are saying that I can filter my pool and have the filter capture whatever needs to be captured without having to run the entire pool water through the filter?

This is what I just can't comprehend. That's like saying I'm going to vacuum my bedroom but only vacuum half of the room and call it a day.
 

ajw22

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I see what you are saying but if we want our filter to capture stuff that falls into the pool, doesn't it have to filter all the water to get it out? I don't see how the filter can get stuff out if it doesn't get to it in the first place.

Get what out?

Most debris that falls into the pool either floats on the surface and should be captured by your skimmer(s) or falls to the bottom to be collected by you pool cleaner.

Finer stuff in the water gets filtered out over time, is not a health hazard, and there is no complelling reason to turn over the water 1 time or 10 times daily.
 
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ajw22

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This is what I just can't comprehend. That's like saying I'm going to vacuum my bedroom but only vacuum half of the room and call it a day.

Vacuuming your bedroom is what the skimmer and pool cleaner does.

Do you look to turnover all the air in your room X times to filter out all dust in the air?

In fact as you vacuum your bedroom you kick dust back into the air. Some of it settles back for the next days vacuuming and other may eventually get captured by any air filters you have in your house.
 

JamesW

TFP Expert
Mar 2, 2011
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So you are saying that I can filter my pool and have the filter capture whatever needs to be captured without having to run the entire pool water through the filter?
If you want a full turnover, why does it have to be a day?

Why not a week or an hour or 42 minutes?

How did you determine that 24 hours is the magic number?
 

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AviatorBimmer

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Vacuuming your bedroom is what the skimmer and pool cleaner does.

Do you look to turnover all the air in your room X times to filter out all dust in the air?

In fact as you vacuum your bedroom you kick dust back into the air. Some of it settles back for the next days vacuuming and other may eventually get captured by any air filters you have in your house.

Exactly, and unless you run your fan on all day, the air inside your home will be full of contaminants, dust, etc. lol
 

JamesW

TFP Expert
Mar 2, 2011
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In any case, you should do whatever number of turnovers that you want based on what works for you.

The most efficient way to achieve one turnover per day is to run the pump 24 hours a day at the flow rate that will achieve your full turnover.

The faster that you run the pump, the more inefficient it is even when you account for running longer.

Also, note that just because you put the entire volume of the pool through the filter, not all of the water actually goes through the filter.

Since the water is constantly mixing, some water will go through the filter many times while some water won't go through at all.

Even if you had 2, 3 or 4 turnovers, there would still be some water that won't go through the filter.
 
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AviatorBimmer

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After reading some of the replies, I get a feeling I could have worded it better.

I'm not insisting on running my pump for 24 hours. I just want to know whats the fastest flow I can run efficiently, which seems to be at 40-45 GPM due to me having 1 1/2" piping.

Thanks for everyone's input.
 
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JamesW

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Mar 2, 2011
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For suction, you want to keep the water velocity below 6 ft/sec. For returns, you want to keep the water velocity below 8 ft/sec.

Size.......6 ft/sec......8 ft/sec.

1.5"...........38...............51 gpm
2"..............63...............84 gpm
2.5............90.............119 gpm
3.0".........138.............184 gpm
4”...........234.............313 gpm

These are the general recommendations for efficient flow.

The amount of power used increases exponentially by a cube factor as the flow increases.

For example, if you double the flow rate, the power increases by 8 times (actually about 6 to 8 times).

So, even though you are running longer, it is always more efficient to run as slowly as possible.

Going at half of the flow rate for twice as long will use 1/3 to 1/4 of the total amount of energy (kilowatt hours).
 
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AviatorBimmer

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For suction, you want to keep the water velocity below 6 ft/sec. For returns, you want to keep the water velocity below 8 ft/sec.

Size.......6 ft/sec......8 ft/sec.

1.5"...........38...............51 gpm
2"..............63...............84 gpm
2.5............90.............119 gpm
3.0".........138.............184 gpm
4”...........234.............313 gpm

These are the general recommendations for efficient flow.

The amount of power used increases exponentially by a cube factor as the flow increases.

For example, if you double the flow rate, the power increases by 8 times (actually about 6 to 8 times).

So, even though you are running longer, it is always more efficient to run as slowly as possible.

Going at half of the flow rate for twice as long will use 1/3 to 1/4 of the total amount of energy (kilowatt hours).

Exactly what I needed! And since I have 1 1/2" plumbing to and from my pad, I have to go by the 1 1/2" numbers on the chart, correct?

The fact all my plumbing on the pad is 2", I have to go by the smallest diameter piping on the system?
 

mas985

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I'm not insisting on running my pump for 24 hours. I just want to know whats the fastest flow I can run efficiently, which seems to be at 40-45 GPM due to me having 1 1/2" piping.
It depends on how you define efficiency. If you measure efficiency by GPM/Watt*60 (i.e. energy factor), 40-45 GPM is not going to be the most efficient flow rate for 1 1/2" pipe. The velocities that James posted are for the maximum recommended flow rates for a given velocity in the pipe but higher flow rates usually result in lower efficiency. So for a given VS pump, there is a specific RPM for a given plumbing system that will have the highest EF.

Your signature says that you have a Hayward SP3202VSF pump and for that pump, the best energy factor of 1.5" typical plumbing occurs around 600 RPM with a flow rate of 11.1 GPM and an energy use of 22 watts (30.3 EF). That would be the most energy efficient flow rate & RPM. Running the pump at 51 GPM would require an RPM of 2749 and energy use of 720 watts resulting in an EF of 4.3. Far worse efficiency. However, running at 11.1 GPM may not be the best choice either as most skimmers require at least 15 GPM to operate properly.

So the answer to your question is that it depends on what you are trying to accomplish. Generally, we recommend setting the minimum RPM such that the skimmers are still working (i.e. water travels over the top of the weir door). This is likely to be the most efficient speed while still accomplishing something. Other factors that can dictate RPM are SWGs, Heaters, Solar, etc. Again, it depends on what you are trying to accomplish.
 

AviatorBimmer

Well-known member
Mar 29, 2021
76
Florida
Pool Size
14300
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Plaster
Chlorine
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SWG Type
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It depends on how you define efficiency. If you measure efficiency by GPM/Watt*60 (i.e. energy factor), 40-45 GPM is not going to be the most efficient flow rate for 1 1/2" pipe. The velocities that James posted are for the maximum recommended flow rates for a given velocity in the pipe but higher flow rates usually result in lower efficiency. So for a given VS pump, there is a specific RPM for a given plumbing system that will have the highest EF.

Your signature says that you have a Hayward SP3202VSF pump and for that pump, the best energy factor of 1.5" typical plumbing occurs around 600 RPM with a flow rate of 11.1 GPM and an energy use of 22 watts (30.3 EF). That would be the most energy efficient flow rate & RPM. Running the pump at 51 GPM would require an RPM of 2749 and energy use of 720 watts resulting in an EF of 4.3. Far worse efficiency. However, running at 11.1 GPM may not be the best choice either as most skimmers require at least 15 GPM to operate properly.

So the answer to your question is that it depends on what you are trying to accomplish. Generally, we recommend setting the minimum RPM such that the skimmers are still working (i.e. water travels over the top of the weir door). This is likely to be the most efficient speed while still accomplishing something. Other factors that can dictate RPM are SWGs, Heaters, Solar, etc. Again, it depends on what you are trying to accomplish.

Outstanding post! This opened my eyes to better understanding the bigger picture.

My SWG calls for a minimum of 20 GPM for proper function. At 20 GPM, I can almost guarantee my weir door will also function correctly.

So with that being said, I should find the rpm that would give me say 25 GPM (little bit over SWG minimim) and go with that as my starting point?
 
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AviatorBimmer

Well-known member
Mar 29, 2021
76
Florida
Pool Size
14300
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Plaster
Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-30 Plus

Excellent! Now I know I might be knitpicking here and just overthinking this, but I have my flow meter connected on the 2" piping before the SWG.

If I set the rpm so it gives me 25 GPM, will it be actually faster in the 1 1/2" section of piping? If so, then I should maybe run it a bit lower so it actually is 25 GPM in the 1 1/2" section?

I really love making things complicated lol
 

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