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Air lift circulation in an excavated pond #501346 01/31/19 09:44 AM
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Hi All,

I first posted about this topic a year ago: http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=486287

Bill provided some helpful thoughts, and since then I have been continuing to read and research as much as I can, with many books and back issues from pond boss.

One of my challenges is that I haven’t yet been able to find much information on using air lift pumps to aerate and circulate and excavated pond. To me they make a lot of sense - I can get water flowing while discretely adding oxygen to the water, all with less energy and less maintenance than a traditional pump - but I haven’t been able to find much info on others using airlift.

I’m wondering if anyone has any good links to information on this, or if there are any “gotchas” that I might be missing. Any thoughts are appreciated

Re: Air lift circulation in an excavated pond [Re: ted_1209] #501349 01/31/19 02:20 PM
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What's wrong with regular aeration?

Re: Air lift circulation in an excavated pond [Re: ted_1209] #501353 01/31/19 05:15 PM
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Are you looking to move water from one location / elevation to another, add oxygen, mix, or some combination of those? Air lift pumps are generally used to move water / sludge from one location to another, although they are limited to low head / lift situations. Lots of folks on the forum with more info than I have if they know what you're trying to achieve.


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Re: Air lift circulation in an excavated pond [Re: ted_1209] #501359 02/01/19 12:25 AM
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I would like to excavate the pond to have a twisting river area. I don’t like the idea of having an aerator every hundred feet, but also don’t like the idea of stagnant water. So this is why I am thinking about using an air lift pump to move a high volume/low head amount of water “around the loop”. I also like the idea of having the “bubbles”appear in only one spot that I can hide to maintain a natural look, while still having the aerated water reach all parts of the pond.

What do you think?

Re: Air lift circulation in an excavated pond [Re: ted_1209] #501370 02/01/19 06:30 AM
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Ted, what width and depths are you considering for your "river"? I think you could accomplish your goal with one, possibly two air lift powered circulation pumps.....It would take some decent planning ahead of time in the design phase.

Re: Air lift circulation in an excavated pond [Re: Rainman] #501371 02/01/19 09:17 AM
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Hey Rainman. For the river I was thinking 40 feet wide so I can hit 6 feet deep at 3:1.

Which parts in particular do you think will require the most planning ahead of time?

Also do you have particular good sources on air lift pumps that you have come across?This is the best article I have come across so far: https://wkrec.ca.uky.edu/files/airliftpumps.pdf

Re: Air lift circulation in an excavated pond [Re: ted_1209] #501372 02/01/19 10:39 AM
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I'll try to explain as best I can based on some fluid dynamics education from long ago.

I'd design the "end" of the river to be at about a 3-4 foot depth and the "start" of the river to be at an 8-9 foot depth. The intake of the pump being in the "end" and the output being in the "start".

Depending on your shape and topography, you can use the intake and output in a synergistic way. Using a smooth bore 12 inch PVC pipe with the inlet in the shallow end of the river and the air diffuser pipe TEE in the deepest part, allow the air to have the longest length of rise possible before the bubbles reach a long radius 90 degree elbow pointed in the direction of flow wanted...I would imagine a minimum of 3 pumps would be needed to gain a slow circular flow, and it may require 100 or more feet of pipe in total depending on intake and outflow locations. Put gradual shallowing section of the river in a fairly straight length of river, and then a sharp curve and depth drop into the deep section.....I hope you can visualize my thinking here, as I am terrible at drawing

Re: Air lift circulation in an excavated pond [Re: ted_1209] #501373 02/01/19 10:50 AM
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I think I see what you’re saying. I attached a pic of the shape I am thinking in this post: http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=486287

I was thinking of running twenty 3 inch pvc pipes from one side of the horseshoe to the other, each with a 1 inch airline attached 3 feet below water level. Apparently this is the most efficient way to move the most water (vs bigger diameter pipes, or piping the air further underwater)

What do you think? Do you know of anyone who has done something similar that I can learn from?

Re: Air lift circulation in an excavated pond [Re: ted_1209] #501377 02/01/19 01:32 PM
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If I understand what you are doing correctly, your plan is to install a kind of stationary airlift "dredge." You might want to Google airlift dredging to get some ideas.



You'll never know what ya can catch unless you wet a line!
Re: Air lift circulation in an excavated pond [Re: ted_1209] #501386 02/01/19 02:38 PM
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Ted, are you thinking the airlift pump will be almost horizontal, or is it vertical with an elbow near the water surface to transition to horizontal? I've never seen a nearly horizontal airlift pump, only vertical. Not saying it wouldn't work, but if efficiency is a main driver, you might want most of the "working part" of the pump vertical so the bubble flow interacts with the water column.

Larger airlifts might be less efficient, but you would need far less of them, so I would likely go that route. Just balancing out air flow to 20 separate pumps would be a trick. Maybe 6" pipe size would be good. I would likely run one air line to a point close to the pumps, then have a manifold with individual valves for each pump with some means of observing air flow to each pump to balance the flows out. Or you could use an orifice or other pressure equalizing approach, although that would reduce efficiency as well.

Depth to introduce the air for greatest efficiency involves the compressor as well. 3'feet of water head is very low pressure for most aeration type pumps. I don't think they would be very efficient in that range. Regenerative blowers are very efficient at moving lots of air at low pressure, so that might be an option. If you go that route, make sure you can control the pond depth, as a foot of additional water pressure could exceed the blower's max pressure, reducing flow to zip.

Good luck - hopefully we'll see the river in action!
Dale


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Re: Air lift circulation in an excavated pond [Re: ted_1209] #501405 02/02/19 03:30 AM
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Ted, I would suggest using 3, 12" diameter pipes instead of small diameter. Use 9" membrane diffusers placed in the deepest possible position with a vertical rise and a long radius elbow to direct your flow. You could put a 2" "vent" at the top of the vertical rise to bleed the air off with minimal flow change. The inlets of all lift pumps can extend into your 3 foot diameter connection pipe.

Last edited by Rainman; 02/04/19 06:08 AM. Reason: Wrong name
Re: Air lift circulation in an excavated pond [Re: Rainman] #501463 02/03/19 09:49 PM
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Hi Everyone,

I want to use an airlift pump to "pull" water around a horseshoe shaped pond:



Here is what I am thinking for what a cross section might look like where the two ends of the horseshoe meet:


Where the two ends of the horseshoe meet I would install a horizontal pipe through the "dam" that separates the water on either side of the horseshoe. On one side I would add an elbow which would connect into a vertical section. At the bottom of this vertical section I would pump in air. My hope is that the rising air would "pull" water through the horizontal section and up the vertical section, causing a large of amount of water to circulate around the horseshoe with minimal electricity and lots of aeration along the way.

I think you are right that a few bigger pipes would be easier and cheaper to build and maintain then a lot of smaller pipes, so I will probably go with that.

What do you think of the idea otherwise? Would it be an effective way to circulate the water around the horseshoe? Any gotchas you think I might be missing?

Could I pump the outlet side of the horsehoe into shallower water with plants to filter the water?

How deep should I pull the water from on the inlet side of the horseshoe (this will be the deepest part of the pond, about 20 feet to the bottom if I wanted to go that far down)?

Ted

Last edited by ted_1209; 02/03/19 09:51 PM.
Re: Air lift circulation in an excavated pond [Re: ted_1209] #501496 02/04/19 06:44 AM
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Air lifts are quite common in aquatics for the low cost/high volume water movement.

What diameter pipe are you considering using to connect to the "start" of your river?

To use the lift to get water flow through a planted area, the planted area needs to be longer, narrower, and shallower than the "main" river for the best use of plant filtering.

If I recall, you were considering a 30 inch diameter connection pipe between the main pond body and start of the river....If so, consider using a Tee style setup normally used for a pond overflow system...You'll simply use air to reverse everything.

In a 30" pipe, you could create a cluster of several membrane style diffusers to create an astounding amount of water volume being moved. Remember, it is not as important to have air volume as it is the have air surface area, meaning a million tiny bubbles have a vastly larger surface area than one air bubble occupying the exact same volume in water...Membrane diffusers create bubbles measured in micron size. This setup could potentially create 1000's of gallons per minute with only a 4-5 cfm air supply.

The main keys to consider for High volume, low cost water movement is pipe diameter, the longest possible vertical rise of air, and air bubble size. Other less critical considerations are smooth bore versus corrugated pipes, sharp, versus smooth angles, and pipe distance friction loss.

If budget allows, I would suggest pulling water from the deepest point in the main pond pool area. REGARDLESS of budget, use fool proof safety guards on both the inlet and outlet so no swimmer can swim into the pipe for "fun"! (suction really won't be dangerous in and of itself) Use a 10-20% larger diameter inlet supply pipe than the outflow/vertical riser pipe diameter....Have a pro do a site visit to help avoid costly errors....cheap insurance to build right than to repair potential mistake later.

Re: Air lift circulation in an excavated pond [Re: ted_1209] #502355 02/23/19 01:22 AM
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This is really helpful Rainman, thank you. I’ve been trying to find an expert to take a second look, but I’ve been unable to find someone so far. Do you have any recommended experts or info sources for air lift pumps used in this way?

Last edited by ted_1209; 02/23/19 01:32 AM.
Re: Air lift circulation in an excavated pond [Re: ted_1209] #502356 02/23/19 01:27 AM
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Also why does the planted part of river need to be narrower and longer again? I was thinking of having the air lift “exhaust” into an area almost like a wetland: wide. shallow, and maybe 100 feet long, filled with plants. What do you think of this? What is the right depth so that filtering plants can grow, and yet it doesn’t “fill in” too fast?

Also any particular reason why I should pull from as deep as possible? I figure if I get the intake part way down water should still get sucked in from all around, including the deeper areas. What do you think?

Re: Air lift circulation in an excavated pond [Re: ted_1209] #502357 02/23/19 01:37 AM
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A select few have use the air lift to create a current powered stream flow through a short moving water system that provided habitat for stream spawning fish such as shiners, walleye and fall spawning trout. One example I recall had the flow go into a shore based U shaped stream that put the water back into the pond. Ted's example above would create stream conditions between the two sections of pond. An airlift stream could flow across an island.

Last edited by Bill Cody; 02/23/19 01:39 AM.

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Re: Air lift circulation in an excavated pond [Re: ted_1209] #502359 02/23/19 01:58 AM
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My suggestion for narrowing the stream section was to avoid stagnated areas of "swamp" land. You want to pull your worst water out, saturate it with oxygen and return it....You will get poison water devoid of oxygen in summer in the deepest portions. By pulling that water out, it gets replaced by better oxygenated water and allows fish to be able to use areas that are normally lethal. You COULD widen an area for a larger biofilter, yet given the size of the pond, I personally think it would become a net negative on overall water quality...I could be wrong on that, as it all depends....on design, plants, water dept, flow rates, shape....many things.

As for the optimum plant depths...that depends on each species of plant...will is be a marginal, shallow water, submerged....


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