RPM vs GPM

Jump to latest Follow Reply
jmcmd1980

jmcmd1980

Well-known member
Jul 2, 2023
110
Lake Worth/FL
Pool Size
14500
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Jandy Aquapure 1400
Is there a way to estimate gallons per minute based on the RPMs of the pump? My plumbing is 2 1/2 inch plastic tubing, there are three returns in the pool that are 3/4 of an inch openings.

I am interested in this, because I have a manual bypass before the heater and the check valve after. I am trying to get a sense of where I should set my heater bypass so I don’t have to always be adjusting it.

I believe the maximum recommended flow to my heater is 100 gallons per minute. Could I run the priming speed slower, so it does not exceed 100 gallons per minute to the heater, and run the spa at less than 3450 RPM, so it’s also not to exceed maximum GPM the heater sees? Then I could leave the bypass to the heater totally closed at all times and not worry about the heater getting too much gallons per minute pressure when priming, or in spa mode.

Thanks so much

Jim.
 
The pool builder, on installation, told me to crack the heater bypass about 30% open, so the “heater did not get too much flow“ when in spa mode which they set to 3450 RPM. That’s why I was asking if I could run the prime and spa mode/heater speeds at less than 3450 RPM to avoid the maximum gallons per minute limit for the heater.
 
Does your pump lose prime? If not, reduce the priming speed to 2500 rpm and see what it does.

As far as the spa, do you have an air blower?
 
The pump never loses prime, though there is a small air bubble at the top of the pump basket at times. I run the pump at 1750 RPMs most of the time with three champagne spa spill overs at 2750 RPM during the day to help with pH rise issues. I do have a blower. As we move into cooler months in southern Florida, I will be using the spa more than the pool, so I’m interested in how to set the bypass valve to have to fuss with it less.


Thanks so much for the help.
 
Like Jim, I doubt are even close to 100 gpm.

Try the spa at 2750rpm. With the blower, I doubt you will notice the difference.
 
Jimrahbe said:
Jim,

Why do you think you are getting even close to 100 GPM at full speed???

Let's see what our "Chart Master" says ..... Calling @JamesW

Thanks,

Jim R.
Click to expand...
I wish I had a flow meter to solve this question. The pool build is only four months old, and I’m trying not to change much in the installation due to warranty issues.
 
jmcmd1980 said:
The pool builder, on installation, told me to crack the heater bypass about 30% open
Click to expand...

Jim,

What happens if you just leave the heater by-pass set to 30%???

Seems to me the by-pass should by-pass the heater completely when you don't use the heater, and that when you do use the heater, it would send all the water through the heater.

Thanks,

Jim R.
 
mknauss said:
Like Jim, I doubt are even close to 100 gpm.

Try the spa at 2750rpm. With the blower, I doubt you will notice the difference.
Click to expand...
Jimrahbe said:
Jim,

What happens if you just leave the heater by-pass set to 30%???

Seems to me the by-pass should by-pass the heater completely when you don't use the heater, and that when you do use the heater, it would send all the water through the heater.

Thanks,

Jim R.
Click to expand...
Jimrahbe said:
Jim,

What happens if you just leave the heater by-pass set to 30%???

Seems to me the by-pass should by-pass the heater completely when you don't use the heater, and that when you do use the heater, it would send all the water through the heater.

Thanks,

Jim R.
Click to expand...
I have a manual bypass before the heater, and a check valve after the heater. If I open the bypass too much and try to use the heater in spa heat mode or even pool heat mode, the heater will go on and then go right off or occasionally I’ll get that horrible, knocking noise. I’m confused, cause I’ve also read that it’s better for the heater not to always get full water flow, thus the development of the versa flow for my heater, which I don’t have.
 

Enjoying this content?

Support TFP with a donation.

Give Support
You can do a spring bypass, which will open at a specific pressure.

For example at 2 psi, the spring opens at 40 gpm.

At 3 psi, the spring opens at 46 GPM.

At 5 psi, the spring opens at 60 GPM.

I would do a 3.5 lb or 5 lb spring bypass.

You can install a flow switch on the heater to verify good flow.

Flo Control Valve, Check, 2 In, 5 Lb Spring (1095-20) - INYOPools.com

1095-20 - VALVE, CHECK, 2 IN, 5 LB SPRING (1095-20)
www.inyopools.com www.inyopools.com

1698012078993.png




Gas Pool Heater: JXi Pool Heater | Jandy

Looking for a Gas Pool Heater? Find the JXi Pool Heater for the Perfect Pool Experience. Buy Now w/ a Pool Pro Near You!
www.jandy.com www.jandy.com


1698012403442.png

I got lucky...now I need help adding a flow switch

Evening, TFP World! We have an autocover that stays closed except when the pool is in use or needs to be left open to breath. Today, it was a beautiful day, so I left it open most of the day. I did not appreciate how much Crud was coming off the trees, and allowed both skimmer baskets to get...
www.troublefreepool.com www.troublefreepool.com
 
JamesW said:
You can do a spring bypass, which will open at a specific pressure.

For example at 2 psi, the spring opens at 40 gpm.

At 3 psi, the spring opens at 46 GPM.

At 5 psi, the spring opens at 60 GPM.

I would do a 3.5 lb or 5 lb spring bypass.

You can install a flow switch on the heater to verify good flow.

Flo Control Valve, Check, 2 In, 5 Lb Spring (1095-20) - INYOPools.com

1095-20 - VALVE, CHECK, 2 IN, 5 LB SPRING (1095-20)
www.inyopools.com www.inyopools.com

View attachment 537028




Gas Pool Heater: JXi Pool Heater | Jandy

Looking for a Gas Pool Heater? Find the JXi Pool Heater for the Perfect Pool Experience. Buy Now w/ a Pool Pro Near You!
www.jandy.com www.jandy.com


View attachment 537029

I got lucky...now I need help adding a flow switch

Evening, TFP World! We have an autocover that stays closed except when the pool is in use or needs to be left open to breath. Today, it was a beautiful day, so I left it open most of the day. I did not appreciate how much Crud was coming off the trees, and allowed both skimmer baskets to get...
www.troublefreepool.com www.troublefreepool.com
Click to expand...
That sounds great. I assume I’m still under warranty so I’ll run it by the pool builder and see if they would install some thing like that before looking elsewhere.
 
  • Like
Reactions: JamesW
Check the heater inlet temperature and compare it to the outlet temperature to see what the temperature rise is.

The SWG temperature is the heater outlet temperature.

The Temperature rise is Outlet - Inlet = Temp. Rise, which should be 16.8 degrees or less.
JamesW said:
You can use this formula to estimate the flow based on the temperature rise.

Y = temperature rise.

X = flow in gpm.

Y = 672/X

X = 672/Y.

For example a flow of 40 gpm should be a temperature rise of 16.8 degrees.

A temperature rise of 11.2 degrees should be about 60 GPM.

As you can see, flow below 40 gpm results in a big temperature rise.

If the water temperature is 86 degrees and water boils at 212°F, then a temp rise of 126 degrees will result in boiling of the water and the heater will probably explode or be seriously permanently damaged.

A flow of 5.3 GPM or less will likely cause the water to boil and seriously damage the heater.


plot Y = 672/X, y from 6 to 60 - Wolfram|Alpha

Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.
www.wolframalpha.com www.wolframalpha.com


plot Y = 672/X, y from 6 to 150 - Wolfram|Alpha

Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.
www.wolframalpha.com www.wolframalpha.com
Click to expand...

You can use this formula to estimate the flow based on the temperature rise.

Y = temperature rise.

X = flow in gpm.

Y = 672/X

X = 672/Y.

For example a flow of 40 gpm should be a temperature rise of 16.8 degrees.

A temperature rise of 11.2 degrees should be about 60 GPM.

As you can see, flow below 40 gpm results in a big temperature rise.

If the water temperature is 86 degrees and water boils at 212°F, then a temp rise of 126 degrees will result in boiling of the water and the heater will probably explode or be seriously permanently damaged.

A flow of 5.3 GPM or less will likely cause the water to boil and seriously damage the heater.


1691862652669-png.521732

plot Y = 672/X, y from 6 to 60 - Wolfram|Alpha

Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.
www.wolframalpha.com www.wolframalpha.com


plot Y = 672/X, y from 6 to 150 - Wolfram|Alpha

Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.
www.wolframalpha.com www.wolframalpha.com


1691863404397-png.521742
 
Haven't we already covered a lot of this?

Setting heater bypass valve

My pool is about 5 weeks from fill. The pool installer gave very little information and training and I have been using TFP for expert assistance. Could someone advise me on setting my heater bypass valve? Should I open it completely to the heater during seasons I use the heater for the pool...
www.troublefreepool.com www.troublefreepool.com

Gas heater needs 2750 RPM to fire

The pool builder set my Jandy filter pump to run at 2250 in pool heater mode and 3450 in spa mode/spa heater mode. They set the system to run at 2750 RPM from 9 AM to 6 PM and gave no further instruction. I have been experimenting with variable pump speeds to save electricity. I have been...
www.troublefreepool.com www.troublefreepool.com
 
JamesW said:
Your flow is likely to be where the system curves intersect the pump performance curves.

For example, if the speed is 3,450 RPM, then the flow is probably between about 86 and 94 GPM.

If you can get the filter pressure at the speeds listed on the graph, I can give you a better idea.

View attachment 537014

Click to expand...
These are my filter pressures at various RPM's:

Heater bypass is fully closed
Spa Spillover Makeup valve is open 50:50 pool:spa

RPM PSI
600 RPM <2
1200 <2
1730 4
2065 10
2400 13
2600 15
2800 18
3000 21
3450 27

Jim
 

Enjoying this content?

Support TFP with a donation.

Give Support
You must log in or register to reply here.
Thread Status
Hello , This thread has been inactive for over 60 days. New postings here are unlikely to be seen or responded to by other members. For better visibility, consider Starting A New Thread.
Top Bottom
Back
Jump to latest Follow Reply