Air Lift Pump Help/Questions

[wld1783]

I'll be moving next year and plan on upgrading my 330 gal to a 500-600 gal. I will have a separate equipment room and plan on using the 330 gal tank as a refugium.

What I'm concerned with is the high electricity costs and heat. The equipment room will be directly ventilated outside so humidity will not be a factor.

I recently pulled a 2 amp pump off my MyReef Skimmer and plumbed the skimmer directly to the overflow. Bubbles are provided by a 1/2 amp 4.2 CFM Whitewater air pump and five airstones. Wow what a difference. More foam/air and 1 1/2 amp savings not to mention less heat and plankton friendly.

The Whitewater air pump kicks a!@. I tried it plumbed directly to 2" pvc with 24" of water column. It moved a lot of water.

- Does any one know how to determine how much water flow?

- Will smaller or larger bubbles make a difference?

- What is the maximum practical height I can raise the water? I was thinking 3"

- I would like to move 2000-3000 gph as this will provide most of the circulation in the main tank. If the refrigium is 3" above the main tank and has a footprint of 72" X 36", will I have enough return pressure through 4 2"PVC return lines to accommodate 2000-3000 gph?

My goal is to use only a single ampmaster on two sea swirls and airlift pumps for circulation between the main tank and refrigium.
Any comments or suggestions will help.

Bill

...Its times like this I wish I took that fluid dynamics class...

[crystalball]

I have (3) 1 1/2 thirtyfive foot pool hoses from my skimmer to my sump, im pumping 5000-7000 gph but im at my top limit, I pull any mor and my tank wont drain fast enough....so going (3) 2" will surly do it without question, do watch the air your pulling into your tank by the air pump, use hepa filters if you can, I too will try this aproach, so I will tag along onto this thread...

[SAT]

The best reference for airlifts that I've seen is in Spotte's Seawater Aquariums, 1979. His table shows a 80% submerged 2"x24" airlift should deliver about 1200GPH. Other people using these tables have found them to be very conservative.

Note that 24" is quite short for a 2" airlift. You'll get higher efficiency (more water lifted per unit of air) by using multiple narrower tubes. For best efficiency, shoot for about a 40:1 length:diameter ratio or more. At optimal efficiency you can get about as much water moved as air injected. At a 10:1 length ratio and 80% submergence, you probably won't do better than 1:3 water:air.

A way to lengthen the tube is to run it from the floor of the room instead of the bottom of the tank (requires more plumbing). Note I don't mean from the sump -- you need full pressure from the tank water level to make this work.

Bubble size isn't relevant to the equation -- you just want them to be even. A diffuser may be necessary to get an even size.

Efficiency drops off rapidly as you raise the output level. The important thing is the ratio: distance above the water level to total airlift height. You'll get some water delivered even at 50%. This is another reason to use a longer tube.

I have 5 1.5"x60" airlifts returning water to my 300G. I find each lift delivers 500-1000GPH depending on how hard I drive it. It makes a lot more noise (gurgle & pop) when I drive it at the higher capacity. I don't use a diffuser and that may be part of the noise problem.

[wld1783]

Thanks crystalball & SAT.

I was thinking more along the lines of a carbon filter but a Hepa filter sounds great.

As far as running the lift to the floor to improve efficiency... outstanding. Do you think it matters much where the inlet is located? If I'm going to run PVC to the floor, using an existing overflow might simplify plumbing and reduce the need to drill the back of the tank.

Any more good Ideas?

Bill

[SAT]

You can use an existing overflow hole, but you don't want to use a fancy standpipe. Basically you want the overflow chamber (if you have one) to be pretty much flooded (maximum water height yields maximum efficiency) and the downward water flow to be unimpeded.

You'll want to use decent size plumbing to keep the head loss down. Airlifts can move a lot of water, but not against any significant head.

[crystalball]

hay sat can yoou e-mail me a pic of your stand pipes/system, I want to run 3000-5000 gph 4' above my sump... are you stating that the water is rising 5' above your sump to flow back into your tank?

[crystalball]

would help to post my e-mail...lol...

njob408@mindspring.com

[SAT]

Originally posted by crystalball
hay sat can yoou e-mail me a pic of your stand pipes/system, I want to run 3000-5000 gph 4' above my sump... are you stating that the water is rising 5' above your sump to flow back into your tank?
Sorry, pictures aren't handy at the moment. No, I'm not using an airlift to return from a sump. For all practical purposes that's impossible. What I do is take water from the tank, drop it to the floor, then airlift it back in a closed loop. Generally speaking, you shouldn't plan to lift more than a few inches above the water level in the source vessel.

BTW, I understand that lifts taller than about 4' can be dangerous because you can get supersaturation of nitrogen from the air injected under pressure. In other words, you can give your fish the bends. My lifts are slightly longer than that so I'm taking a chance.

[crystalball]

well I dont know about the bends, my pumps are sucking a little air due to the high volume, then run through 35' worth of hose, the air comes out supper fine, and the fish have no problem with this...I was tring to use this in my sump to pump water up to my filter boxes, if I could do it by air it would free up a few large pumps and be cheaper to operate.

[piercho]

In testing a 1.5" X 4' lift, I got a little more lift from injection of small bubbles than larger bubbles. To get an even dispersion of bubbles with no intrusion into the lift column, I inject the bubbles in thru holes in a cross-section of the pipe. I call this "ring" injection, for lack of a better word. Here is a link to my DIY ring injector: http://archive.reefcentral.com/forums/showthread.php?s=&threadid=136607

I've been using a 20GPM lift as the main circulation for a 65G tank for the last 2 months. Overall, I'm happy with the results. I took some pics of the final installation (it's a lift + RCSD) and should get them back Saturday. If any are worthwhile I'll post them on a thread in the DIY forum shortly thereafter.

Read thru this thread and you'll find where I posted estimated flow for 2' and 4' lifts (this is raw, un-empeded flow for in-tank lifts): http://archive.reefcentral.com/forums/showthread.php?s=&threadid=144863 These flows are higher than the values computed using the Spotte formula, and are for 8-point ring injection.

One more thing to add to your why air-lifts are good list: I'm pretty sure mine will cure my summer tank overheating problem. Have to wait for summer to see, though...:)

[wld1783]

Thanks again for the replies. Everything has been helpful.

It still seems that height is an issue. Would it be possible to achieve a flow of 1200gph 6" over the main tank using 6' of 2" PVC and about 2 CFM of air?

Also are there any ideas on reducing the bubbles returning to the main tank? I know microbubbles are a pain. I am hoping that as long as the return is around 24" lower than the outlet of the airlift, most of the bubbles will remain in the refugium. I dont want to design a refugium with baffles.

As far as the bends, I believe that deals with partial pressure. As long as the tank pressure remains constant I dont think the nitrogen bubbles in the fish blood would come out of solution.

Bill

[piercho]

"It still seems that height is an issue. Would it be possible to achieve a flow of 1200gph 6" over the main tank using 6' of 2" PVC and about 2 CFM of air?"

If you have a total lift heigth of 6', and are only lifting the water 6": easily. I'll see if I can't get an estimate from my copy of Spotte, tomorrow.

[piercho]

Well, the numbers for flow vs injection volume don't bounce out to what I find to be reasonable. This may be because Spotte is using a single-point of injection rather than perimeter injection for his figures and tables. I don't know.

For your lift dimensions, % submergence, and injection volume; a 2" pipe diameter looks like a good choice.

I didn't try a single-point injection when I tested my lift. I tried 8-point, and then maybe 100 points as shown in my DIY thread. I did get slightly more flow with more and finer bubbles, but I also get more micro-bubbles in the return. IMO a 8-point ring injector is probably an optimum compromise, using a 1/16" or 1/32" bit to drill the holes for injection volumes around 2 CFM. If you use my DIY design, you can easily build a couple of lifts for not too much money and play with them to see what you get.....

As a point of reference, I get >1200 GPH using <1.5 CFM injected into a 4' X 1.5" lift. That includes a lot of plumbing resistance that is cutting my potential flow way down. For your application, you can get a LOT more flow.

"- Does any one know how to determine how much water flow?"
From Spotte: "There still is no widely accepted equation for the airlift pump design"
2 models for optimum flow:
Q=[0.504 * S^(3/2) * L^(1/3) - 0.0752] * D^(5/2)
Q=[0.758 * S^(3/2) * L^(1/3) + 0.01196] * D^(5/2)
where
Q=flow/minute (L/min)
S=length of pipe submerged (cm)
L=Total pipe length (cm)
D=pipe diameter (cm)
Both of these equations are too conservative, IME.
For the injection rate at optimum flow, for the lift dimensions you give: V(water)/V(air)=0.75. This is where I don't believe the results that I get.

"Will smaller or larger bubbles make a difference?"
Getting an even dispersion of bubbles at the area of injection is what makes the big difference, IMO. This is where a ring injector with multi-point injection is good because you get even dispersion without any intrusion (drag) in the lift pipe.

"- What is the maximum practical height I can raise the water? I was thinking 3"
40% submergence is the limit. Actually, flow goes to crap with less than 75% submergence, so I'd try to have >75% submergence.

"If the refrigium is 3" above the main tank and has a footprint of 72" X 36", will I have enough return pressure through 4 2"PVC return lines to accommodate 2000-3000 gph?"
IMO, yes. If you have a copy of "Dynamic Aquaria" Adey/Loveland, there is a diagram (from a Spotte book!) of almost EXACTLY this application.

Everything that SAT stated in his posts looks right on the mark, IMO/IME.

Good luck.

[wld1783]

Thanks Piercho

All this helps. I give your DYI design a try.

Bill