Relationship between HP head loss and GPM?

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yanndoray

0
Oct 24, 2016
13
chapel Hill/NC
Hi,

I am trying to figure out the pump I should choose to replace mine.
I have a above ground 19000 Gallons. I have calculated a 40 GPM.
My sand filter can handle 50 GPM.

My big question mark is about the heal loss of my installation.
I have come up with a number that seems to be outranging : 100 foot head with 80 feet 1 1/2 pipes ten elbow, 1 valve 1 T.
Ten 90 degrees elbow is pretty common and this alone is 70 foot head. Right?
Is there something I am doing wrong? I am following numbers found online.

Which confuse me because specs of pump usually don’t go that high regarding the foot head.

Any recommendation on pump specs would be helpful or thought on foot head calculation.

Thank you
 
yanndoray said:
Hi,

I am trying to figure out the pump I should choose to replace mine.
I have a above ground 19000 Gallons. I have calculated a 40 GPM.
My sand filter can handle 50 GPM.

My big question mark is about the heal loss of my installation.
I have come up with a number that seems to be outranging : 100 foot head with 80 feet 1 1/2 pipes ten elbow, 1 valve 1 T.
Ten 90 degrees elbow is pretty common and this alone is 70 foot head. Right?
Is there something I am doing wrong? I am following numbers found online.

Which confuse me because specs of pump usually don’t go that high regarding the foot head.

Any recommendation on pump specs would be helpful or thought on foot head calculation.ysmfor itself up till

Thank you
Click to expand...

Part of what may be tripping you up, is velocity. with one foot of head, you will get water to flow out of 80' of 1.5" pipe. The how much is where head pressure comes into play.

So take pooldv's advice!

and a few thoughts.

1) bigger pays for itself up to a point. Kind of like a chain. If you have a weak link (e.g, highly restrictive filter) balancing. That with a less restrictive filter will pay off directly. Getting a filter that has even far lower head loss won't help much because now something else in your system will dominate your losses.
2) pumps have a sweet spot where they can move a lot of volume at a low speed, if th system has low enough flow friction.
3) Two- or variable-speed pumps give you good power/suction for when you want to really move some water quickly, and yet can be a small fraction of the cost of operation if they mostly run on low speed
4) Longer pump run times at lower flow rates cost a lot less over time to achieve the same result. The power goes approximately as a 3rd power relationship, so if you run your pump at 100 watts a xGPM, it can be as high as 800 watts at 2xGPM. So a two speed pump can pay for itself quickly, unless you must have short run times.
4) pumping does not sanitize. It is helping you keep everything mixed up, and removing fine particles that are suspended in the water. so lots of pumping of algae infested water, will just mix up the algae.
 
Good points. A 2 speed pump will use less than 1/4 the electricity and move half the water volume on low speed as it does on high. I run my VS pump at 1100 rpm for filtering, skimming and making chlorine with the SWG and it uses 150 watts at 1100 rpm. At 10.25c/kWh I can run my pump at 1100 rpm 24x7 for less than 12 bucks a month. Pool filters are much more efficient at lower flow rates than they are at higher flow rates.
 
yanndoray said:
Any recommendation on pump specs would be helpful or thought on foot head calculation.
Click to expand...
Don't bother trying to calculate head. it is very difficult to do accurately. Head loss is dependent of flow rate and flow rate is dependent on head loss so you need to determine the plumbing curve for your system and where it crosses the pump's head curve. However, if you have an operating pump, you can just use the filter pressure to estimate flow rate. I have a spreadsheet in my sig that helps with that.

But in reality, you don't need head loss to choose a pump. If you are trying to match the sand filter's flow rate, I think you would be safe with a 1 HP two speed Dynamo or Optiflo pump. Pentair pairs larger pumps with smaller filters for their AG systems. On typical AG plumbing, both pumps will deliver less than 50 GPM.
 
Interesting point. 2 speed pump might be the way to go.
Is that correct to say, I would have the lower speed for regular filtering process and higher speed if I need to use a cleaner of mix my chemical faster.

My concern is the following : Is that okay to process the flux at a higher rate than the filter (for me 50GPM max) even if it is only momentarily?
I have read it might damage it.

Thank you for your inputs. Very helpful.
 
Sand filters are probably the most robust of all filters. As long as the flow rate is not really high (e.g. 2x), the worst that can probably happen is that dirt might get pushed all the way through the filter. BTW, what pump model do you have now?
 
At the moment : Hayward SP1600 with a 3/4HP A.O. Smith Corp.
But the motor is dead and the pump housing is in a bad shape.
I am about to purchase a new one.

I have been expanding the plumbing and the pump and filter will be now 20 feet (and four 90 dares elbow) farther.

I am considering this model : Hayward SP1775 Power-Flo II 3/4-Horsepower Above-Ground Pool Pump.
It is not a 2 speed but it might do it. It is pretty cheap.

I would like to be able to check the flow. So I guess some sort of flow meter would help me to monitor the flow and make sure my installation is proper.
I have found a Flow meter but not sure this is what I need for my 1.5” plumbing.Flowvis Flow Meter, Retrofit Kit For Jandy Check Valve 1.5", FVJ-R-15, GPM


any advice would be appreciated.
 
Where did you get that pump number. It sounds like a part# for a SuperPump which has much higher flow rates than the pumps we have been talking about. Does your pump look like this:

Super-Pump.jpg
 

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The motor on that pump is a 3/4 HP A.O. Smith. It just might be a different color. Hayward doesn't make motors but usually uses A.O.Smith.

The number on the basket is a part number for the basket not the pump number.

On the label of your pump should be something called "Service Factor" or "SF" what is the number or is it missing?
 
So the 3/4 HP PowerFlo LX or Matrix would have about the same flow rate as your current pump. But the 3/4 HPs only come in single speed.
 
Unfortunately, I have never seen the pool running and I don’t know it history. I have bough a pool with black water, a broken pump and zero knowledge.
Based on what you have found out and the few I know, it sounds the previous owner had a super pump but then replace the motor with a 3/4 HP SF 1.0 that now is dead.
The housing being pretty old I am about to change the whole set up.

[FONT=Arial, sans-serif]Pentair 347990 OptiFlo Vertical Discharge Aboveground Pool Pump with 2 Speed Motor and Standard Plug, 1 HP[/FONT]

[FONT=Arial, sans-serif]Might be a good option as well.

Thank you Mark.
Now I have to figure out a way to monitor the flow of my system. I have opened another thread for that.

Cheers[/FONT]
 
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