DIY air lift pump through gravel suction grid to return jet design.

[combatwombat]

I have two needs that are currently unmet in my new pond design.

1. Some way to keep the bottom clean.
2. A return jet in an anticipated dead spot.

There are lots of ways to achieve both of these independently. For #1, I have seen a gravel suction grid used successfully in a number of fish ponds. #2 is also easy using PVC to create a return jet from your pump or using a low voltage pond powerhead or something similar.

But what if you could achieve both with a single, extremely efficient air lift pump? Air lift pumps can move a lot of water with very little energy, but they can't achieve any head height at all, so they're really only good for circulation or to push to a gravity filter.

Here's a drawing I made that would explain how this idea would work:

The intake for the air lift pump would be a gravel suction grid at the bottom of the pond, covered in pond gravel, which would colonize bacteria that would break down waste as water is pulled through the grid.

The output would be plumbed just below water level in the dead zone to create surface agitation and push any debris there back into the path of the natural current to the skimmer.

I can't find a lot of into on designing air lift pumps, but they seem relatively simple. I have no idea if this will actually work or not, but it seems like it ought to.

Can anyone provide guidance on this design?

 

[gello22]

I have seen similar designs with high volume air stones that were used as foam fractionators. I'm not sure what design detail converts it from generating protein rich foam to a pump. I think it would be more likely to end up with a foam pump vs a water pump. of course I only have experience trying to make the foam. I have a 40cfm air pump and I tried it with a 3" pvc pipe and I would say it didn't work as either a pump or foam fractionator. I did have plastic mesh inside to try and break up the bubbles more since foam was my goal. I could imagine losing the stone making large violent air bubbles in a pipe might do the trick. I would plan on adjusting the pipe diameter to try to find the sweet spot.

 

[combatwombat]

Thanks @gello22. I don't know a thing about foam fractioners, but while doing some furious reading about the subject, I actually found two articles on Pond Trade Mag penned by a guy named Mike White describing almost exactly what I drew above. I think you would have to be really dialed in with your calcs to make it work right with an air lift pump since they're a bit finicky, but it's good to know someone who knows what they're doing endorses the plan.

Thanks for the tip on the bubbles. I didn't even know what an air lift pump was when I started building my pond and am now realizing that I may not have an ideal place to locate one anyway as I have shelves all the way around my pond, so would need 2 elbows to get to the full depth of the pond unless I was okay having a pipe sticking up somewhere in the middle.

 

[Solar guy]

I'd say it's possible. Your proposal looks exactly like an enlarged version of an aquarium bottom filter.

As a foundry engineer I once made a fluidizing sand fountain. We lifted sand up 20 feet in a 6" pipe using nothing but air. Dry sand, and many other granular solids, can be fluidized and behave just like water. We did it to separate metallic particles from the sand due to the different density.

Anyway, back to your question. In my calculations I determined I could lift 100 gallons water per hour about 4 feet with a 45 watt air pump. Hope that helps. the process should be scalable to what ever volume and height you need.

 

[combatwombat]

Thanks @Solar guy. I don't need any head height at all, actually, as the plan would be to return the water to the pond below the surface. I think I would want to get 1000 gph with a 40L air pump, otherwise it's probably not worth doing

The main "problem" I have is that I don't have much depth for pipe. Just 30" or so. I think that will greatly limit what I can flow, but I've not found much design criteria (at least that I can read) that would tell me what I could expect to flow at different pipe lengths/diameters/volumes of air. Most of the projects like these I've seen are dealing w/ 6' or more of water in a koi pond or natural swimming pool.

If you have any thoughts about that, would love to hear 'em.

 

[islandboy]

Your idea is how aquarium under gravel filters work. Most of them are less than 30"
aquarium under gravel filter - Bing images

 

[combatwombat]

Your idea is how aquarium under gravel filters work. Most of them are less than 30"
aquarium under gravel filter - Bing images

That's true, but most aquariums are pretty tiny compared to a pond, so the flow you get at <30" might be sufficient in an aquarium and totally useless in a pond. I don't know, though, because I have no idea how to determine flow rate at different depths besides just building it and seeing if it works!

 

[Jhn]

Also most of the use of undergravel filters in aquaria at least in the saltwater side is a dated( for like over 30 years) and no longer used practice because it just ends up becoming a big nitrate factory degrading your water quality, in a well planted pond with a bog though it could probably be counteracted. Either way as I said before it looks like something that would require maintenance on your part to keep it functioning properly, for me I try to make my ponds as close to no maintenance as I can get them

 

[combatwombat]

@Jhn: That was my thought, too. I think they're nitrate factories in an aquarium because they don't work with plants, which would consume those nitrates. Lots of places to fix that nitrate issue in a pond. Especially, like you said, when you have a bog. And better to have too many nitrates than too much ammonia, no?

Either way as I said before it looks like something that would require maintenance on your part to keep it functioning properly, for me I try to make my ponds as close to no maintenance as I can get them

Same concern. I'm only considering it because the proponents of it swear up and down that they're practically maintenance free. I believe them. But like all things pond, there are so many variables. Who knows if the pond would have been just as maintenance free without them. I don't think anyone is doing any real controlled studies of this stuff for water gardeners so all we have to go on are anecdotes.

 

[gello22]

maybe you already stumbled on this guy in your research he does some experiments where he gives his air pump specs 3 pipe diameters and a few head heights and some rough flows. Perfect for some ratio engineering math. seems it is also sensitive to the pipe length in the water, ie you need enough length.

davidpaganbutler

 

[combatwombat]

maybe you already stumbled on this guy in your research he does some experiments where he gives his air pump specs 3 pipe diameters and a few head heights and some rough flows. Perfect for some ratio engineering math. seems it is also sensitive to the pipe length in the water, ie you need enough length.

davidpaganbutler

I think I saw that video some time ago, but it got lost in the sea of tabs. Thanks for resurfacing that for me. There are tons of videos about air lift pumps on Youtube, but 99% of them are awful. That one is pretty good. Depth of submergence is the issue for me. I think you either need to design your pond with air lift in mind or be lucky enough to have a spot that will work well.

 

[GBBUDD]

for me I try to make my ponds as close to no maintenance as I can get them

Maintenance free, and if it costs me a bit in electricity soooooooooooooooooo beeeeeeeee it . if i can walk away from my pond for a month at a time come home to what i do and have no issues im all about it