Myth on increasing pipe diameter?

[mr.maroonsalty]

Let's say it's some number with a 1000 zeros... Or if you want a literal interpretation it's some number multiplied by 10000...doesn't matter. If head height isn't an increase in water weight then what is it? Obviously, any sort of propulsion equation must figure in the weight of the object being moved.

 

[jerpa]

A propulsion equation would take the mass of the object into account. "Weight" would be one of the forces taken into account and would be derived from mass and gravity.

The height from the measured point to the water line is what is important. The total weight of the water will increase in a larger pipe but it is irrelevant.

 

[mr.maroonsalty]

I see it's all about psi. Pressure is what stops the lift not weight, the only way to make H2O more dense is to add something like salt to it. Still doesnt make perfect sense that weight of all the liquid that a pump is pushing has nothing to do with how well it performs but, I'll make the leap if it is simply about 1 inch3 weight.

I may have added an extra 100th of a pound per inch3 or so by adding salt at the time of swap from 1.5" to 2" but I'm not certain. Regardless I shortened my total run a couple inches, changed 2 1.5" nozzles with 2", and switch two standard 45 el for a long radius sanitary 2" 90 el and needed to cut my drain valve a very tiny bit.

 

[Aqualund]

I see it's all about psi. Pressure is what stops the lift not weight, the only way to make H2O more dense is to add something like salt to it. Still doesnt make perfect sense that weight of all the liquid that a pump is pushing has nothing to do with how well it performs but, I'll make the leap if it is simply about 1 inch3 weight.

I may have added an extra 100th of a pound per inch3 or so by adding salt at the time of swap from 1.5" to 2" but I'm not certain. Regardless I shortened my total run a couple inches, changed 2 1.5" nozzles with 2", and switch two standard 45 el for a long radius sanitary 2" 90 el and needed to cut my drain valve a very tiny bit.

It's hard to figure out exactly what you're talking about...so it's hard to tell you if you are on the right track or not. But just simplify it: bigger pipe is better. You're going to get better performance with bigger pipes and fewer 90 degree elbows.

 

[das75]

always wondered why see on calculators and tables 2-45° (long sweep) have more loss than a single 90°?

 

[BeanAnimal]

Still doesnt make perfect sense that weight of all the liquid that a pump is pushing has nothing to do with how well it performs but

You stand on the beach and are able to breathe, with the weight of all of the air on the planet around you, pressing in your lungs (a pump). You get into a spaceship and fly to mars. The spaceship has air inside that is pressurized to 1 atmosphere. Space has no atmosphere. You breathe with the same effort in your tiny artificial atmosphere as you did on earth because your air pump (lungs) see the same fluid pressure they did in earth.


As for the pump and "weight": Lets say the pump is capable of 100GPH. Seawater weighs around 8.5 pounds per gallon. So the pump is capable of moving about 850 pounds of water per hour.

As the pipe size increases, the volume of water stays the same (lets ignore the resistance of the pipe walls and turbulence). Lets say in a 2" pipe the water moves 10 feet per second. If we increase the pipe diameter to 3" and we are still only moving 850 pounds of water per hour, what happens? Well, the same amount of water is moving, but the rate of travel is much lower. How much lower? The original pipe has an cross-section of about 3.14" and the 3" pipe has a cross-section of 7.1". That means at a flow rate of 850 pounds per hour (100GPH) the water moves about half as fast in the 3" pipe as it does in the 2" pipe.

No leap here... just simple physics.

 

[BeanAnimal]

always wondered why see on calculators and tables 2-45° (long sweep) have more loss than a single 90°?

A lot depends on the flow rate and resulting turbulence in the bends. For our purposes, either will do.

The short 90 creates turbulence, but does so in a short space with only (2) transitions (in and out). The long 90's add pipe as well as fluid transitions (4). The numbers you see in the calculators are partly based on the fact that the plumbing parts present "rough" transitions and are not smooth tubing through each transition, etc.

The take away: don't pay much attention to the decimal places, as any "plumbing" calculator is going to be an extremely rough estimator of the real world parts we are using.

 

[Humu Humu]

mr. maroonsalty,

You stated it correctly, it is all about pressure. It's called head loss in fluid dynamics. There is friction head, velocity head, and pressure head. The three add up to your total head loss. When considering the diameter and volume of the pipe, it's pressure, measured in distance above the pump that counts. A one inch diameter pipe at 10 feet above a pump has the same pressure (head loss) on the pump as a 6 inch diameter (or any diameter) pipe would at the same 10 feet distance.

Think of it this way, the pump isn't trying to lift all of the water up and out of the pipe, it's only trying to overcome the pressure at the pump outlet.

As far as friction loss in the pipe goes, I think that, unless the pipes are replaced every so often, that the tubular worms and calcium deposits that grow along the inside of them (observed) contribute significantly to friction head loss for small diameter pipe. I would advise to use larger diameter pipe (exa, 1" instead of 3/4") whenever possible to mitigate this effect. Using a larger pipe reduces the velocity in the pipe. The friction loss due to velocity is V^2/2g. So reducing the velocity dramatically reduces the friction loss (square of the velocity).

So after all that - fatter pipes help.

Hope this helped somewhat.

 

[SGT_York]

Hopefully some of the smarter fluid engineers can make a comment, I understand that PSI and weight are identical regardless of the volume of fluid (pipe dimension) as stated above, I however have personnaly seen a MAG 7 on a straight vertical lift outperform with 1.5" pipe maybe 2" at 4' of head then produce less flow at 12' of head in terms of GPH than with 3/4" pipe. Same pump just increased the pipe diameter after the female thread at the pump?

 

[wolfblue]

I'd also like to point out that two 45's do not equal a 90.

Granted...mostly. Don't get me wrong, I have a decades long irrational hatred of 90's. But I know that if you design it right, 90's don't hurt much.

I have had a good friend who is an aquatics systems designer visit me a few times here. I was complaining to him about one system that I am responsible for, I call it elbow city. It's a 40,000 gallon amazon basin tank with 65 90's and 7 45's. He told me "two 45's is about the same as a 90 anyway."

This guy is not just somebody that calls himself a system designer. He designed two here, 123,000 gallons total. On top of that he is (probably) the one guy on this planet responsible for the most gallons. This company is billions beyond huge. I forget his title, but its same as me, head of life support. Except for him its life sciences something, and he has a stack of PhD's working for him.

Another point is that friction loss per foot is dependent on the pressure or velocity in the pipe.

At one time, no 90's on anything I designed. Now for home/office size tanks, keep your velocity down and use what looks cool. If a couple 90's make the plumbing look more orderly, just do it. If sweeps look cool, and won't get in your way later, do it. Because if you have the right size pipe, it doesn't much matter.
--John

 

[madweazl]

I've never understood how increasing pipe diameter over the pumps outlet size would provide any positive results.

 

[Aqualund]

I've never understood how increasing pipe diameter over the pumps outlet size would provide any positive results.

Niether did I until I did it. At that point I realized just how completely wrong I was.

 

[madweazl]

And there were measuble results from only the diameter change?

 

[SGT_York]

There are within constraints and diminishing returns. Less friction loss caused by slower velocity. But the success rate is very pump system dependent.

 

[mr.maroonsalty]

Look at equivalent length charts for fittings; they tell how many feet of pipe a fitting equals as far as friction loss is concerned. Then comes the problems: I find 90 els that are true corners...they don't have the sweep in the back; which is a 90 el on a chart and which is a sweep? Next, once you get to 2" one can shop the sanitary section where you can find even longer radius 90 el. One can really beat their head up comparing total loses, but even the engineers don't have loss evaluations for every plumbing configuration, so they do what every engineer does; they over estimate and simply apply more preasure whenever they can to avoid any problems.

I have another idea why I saw a slight loss of flow when I upgraded to 2"; my dart wheel is unable to fill both 2" nozzles that run directly from a tee, the 1.5" configuration did seem to fill the nozzles. Might the loss of velocity in the horizontal run to the tee and out the two descending nozzles reduce total flow ever so slightly when compared to the small pipe that is able to maintain its velocity through the entirety of the run? I may not be using the correct jargon, but what I'm basically getting at is, could the 1.5" nozzle act syphon like, whereas, the 2" nozzles can't carry a full pipe of water and in essence the syphon break causes an equal pressure, thus not gaing acceleration?

 

[Aqualund]

And there were measuble results from only the diameter change?

Yes. definitely specific to the pumps I was using and it verified what was on the charts.

Originally I had my coral farm running on 5 reeflo hammerhead pumps all piped in with 1.5" pipe. one of the pumps was for the skimmer, another for the UV and the rest for all the tanks...because It naively made sense at the time.

When I decided to forgo this system, and install a larger pump that could push 12k gph with 2inch inputs and outputs I was very dissapointed to see that the max I could get out of the system was about 6k total...which was way under what I needed...and this was with 2" pipe!

I was confounded and frustrated until I learned from these forums how if you read the fine print of most of these pumps...they get their max gph readings from larger diameter pipes. of course with diminishing returns...there's only so large you can go before it becomes useless.

So I took the leap and spent the money on 3" fittings and pipes and I now push 11,700 gph with my 12,000gph pump. that is double the efficiency it had before...even with a 1.5" restricted input on the pump since the bulkhead was plumbed for the previous pumps.

so now im only running one pump at a fraction of the electricity I was before and I have all of the required movement I need for the beckett skimmer and the UV to do its job...because of bigger pipe.

 

[mr.maroonsalty]

Yes. definitely specific to the pumps I was using and it verified what was on the charts.

Originally I had my coral farm running on 5 reeflo hammerhead pumps all piped in with 1.5" pipe. one of the pumps was for the skimmer, another for the UV and the rest for all the tanks...because It naively made sense at the time.

When I decided to forgo this system, and install a larger pump that could push 12k gph with 2inch inputs and outputs I was very dissapointed to see that the max I could get out of the system was about 6k total...which was way under what I needed...and this was with 2" pipe!

I was confounded and frustrated until I learned from these forums how if you read the fine print of most of these pumps...they get their max gph readings from larger diameter pipes. of course with diminishing returns...there's only so large you can go before it becomes useless.

So I took the leap and spent the money on 3" fittings and pipes and I now push 11,700 gph with my 12,000gph pump. that is double the efficiency it had before...even with a 1.5" restricted input on the pump since the bulkhead was plumbed for the previous pumps.

so now im only running one pump at a fraction of the electricity I was before and I have all of the required movement I need for the beckett skimmer and the UV to do its job...because of bigger pipe.

You nearly doubled the area going from 2" to 3" pipe.

 

[wolfblue]

so now im only running one pump at a fraction of the electricity

Thats why. Less or smaller pumps also could mean less noise.

--John

 

[ATLL765]

Good advice.



This is helpful as well. Do you have a rule of thumb for cleaning out your pipe? Any special brush or tool?

They make this brush for cleaning the coils on your fridge. It's about 2' long brush that is on a coiled wire, so it's bendable. That would work, I'd think.

 

[Lavoisier]

They make this brush for cleaning the coils on your fridge. It's about 2' long brush that is on a coiled wire, so it's bendable. That would work, I'd think.

Something like this?



Thank you.