Pipe Size for Vertical Head

[jda]

Does the pipe size matter for flow rate?

I am asking because the RC head calculator says that bigger is better, but I found the opposite. I ran 10 feet of 1.5" then, cut it down to a pair of 3/4" into the returns drilled through the bottom of the tank - the flow was about 1000 GPH. If I put the pair of 3/4" outlets at 2 feet and ran the 3/4" tube up the other 8, then the output doubled and is too much for my overflow. So... 10 feet of 1.5 flowed less than 2 feet of 1.5 and 8 feet of dual .75s. The only thing that i can figure is that there is less weight in water in the pipes, but I also remember from calculus in college that volume does not matter... but is this in a gravity situation vs a pumping situation?

Does the weight of the water in the larger pipe slow down impellers? Am I imagining this? Is gravity vs pumping up indeed a different equation. Is there an equation to figure this out?

 

[SGT_York]

Yes,

There are volume pumps and pressure pumps, in a volume pump headloss affects flowrates faster than pressure impellers relative to the weight in the water column. With a pressure pump the difference would be minimal. There are some in-depth math calculations I used in a water tower construction design a while back. What kind of pump do you have? The math for a closed system and open system are different formulas. Water towers and aquarium returns are different then an industrial application for a chemical plant the fluidized mechanics are different which leads to a lot of confusion on this subject.

Utah Reefs ran an experiment years ago using a Mag 7 and 9 at 4 feet of head the 1.5" pipe was a clear winner but at 12 the 3/4 pipe produced more flow while the 1.5" stopped.

 

[dppitone]

Yes, to below, it depends on the type of pump you have. Yet generally for best efficiency bigger is not better, because you could get so big that it wouldn't make sense. Rather a good rule is to double the area of the pump output. So if the output of the pump is 3/4", you should step it up to 1" or 1.25". 1 1/8" would probably be right on but that tube is hard to find. I generally use 1.25" tubes for 3/4" outflow pumps.

Yes,

There are volume pumps and pressure pumps, in a volume pump headloss affects flowrates faster than pressure impellers relative to the weight in the water column. With a pressure pump the difference would be minimal. There are some in-depth math calculations I used in a water tower construction design a while back. What kind of pump do you have? The math for a closed system and open system are different formulas. Water towers and aquarium returns are different then an industrial application for a chemical plant the fluidized mechanics are different which leads to a lot of confusion on this subject.

Utah Reefs ran an experiment years ago using a Mag 7 and 9 at 4 feet of head the 1.5" pipe was a clear winner but at 12 the 3/4 pipe produced more flow while the 1.5" stopped.

 

[jda]

I rigged this up. I used a Diablo DC 10500 pump with a 1.25 output. With the 1.5" spa flex, it would pump up about 15 feet, which is what it is rated at. I rigged up a 5/8" garden hose and it would pump up 3 stories from my basement to my 2nd floor balcony as high as I could hold the hose with very good velocity.

I ended up running a 1.5" manifold with 6 outlets. I took dual 3/4 lines up 10 feet to the tank upstairs and used 3 of the others to run tanks in the basement. With the 3/4" lines going upstairs, the pump needs to be turned down for the overflows to drain well enough... with the 1.5" spa flex, it would barely pump up the 10 feet with the other manifold outlets running.

At least in my experiment, smaller pipe will get more head and more flow, at least for this pump.

 

[dppitone]

You're initial post was about flow rate. Yes, if you step down the tube diameter it will result in providing more pressure. So there will be more power, which can be translated to greater head.

But if it's a flow rated pump your also getting less flow relative to power used so it's operating very in-efficiently.It's ok to do that with a pressure rated pump.

The most efficiency is stepping up the cross section area of the tube to around 2x for purposes of flow rate relative to energy used.

Dave

I rigged this up. I used a Diablo DC 10500 pump with a 1.25 output. With the 1.5" spa flex, it would pump up about 15 feet, which is what it is rated at. I rigged up a 5/8" garden hose and it would pump up 3 stories from my basement to my 2nd floor balcony as high as I could hold the hose with very good velocity.

I ended up running a 1.5" manifold with 6 outlets. I took dual 3/4 lines up 10 feet to the tank upstairs and used 3 of the others to run tanks in the basement. With the 3/4" lines going upstairs, the pump needs to be turned down for the overflows to drain well enough... with the 1.5" spa flex, it would barely pump up the 10 feet with the other manifold outlets running.

At least in my experiment, smaller pipe will get more head and more flow, at least for this pump.

 

[jda]

Is there an equation for this that I can check out. I am totally sure that you are 100% right, but I am confused... I am getting more flow by stepping it down because I cannot get any by going that high with the wider pipe... so 1200 GPH with dual 3/4 is better than none with 1.5". Is what you are saying that if I was below the head limit of the larger pipe, that the larger would be better?

 

[dppitone]

Yes there is a forumula and it depends on the head and if it's a flow or pressure pump, but I don't know the details cause I'm not the smart. I just read stuff LOL. If you tried different specs and it works for you than that's good enough.