Thread: Airlifts - pumping water around a gravity system using only air

Hi

I wanted to share with people about this system of pumping water, because once you understand how it works you'll wonder (well I do) why people still insist on using conventional water pumps on a gravity system.

Following my research (I did a lot, as I was skeptical that it would work), I have successfully built one for my pond.

I only use an airlift to circulate all the water from my filters back into my pond - which is around 13,000 litres in size.

What is an airlift?

For those who've not heard of it, an airlift is essentially a long pipe that is submerged vertically in water (or water can be fed up through the pipe from the bottom of the pipe) and by pumping air up through the water in the pipe, the rising bubbles causes water to flow upwards.

This upwards water flow is essentially caused by the bubbles expanding as they rise to the surface, which causes the water to then fill the void caused by the bubbles as they go up.

Once the air bubbles/water flow reaches the top of the pipe, all you need to do is give the air a chance to escape and the water somewhere to go.

In our case, the water flowing into the bottom of the airlift will be water coming from your filters and the water flowing out the top will be flowing back to your pond.

To see one in action, check out this video, which uses coloured balls and clear perspex pipes showing how an airlift works:

So what are the pros and cons?

Pros:
Most importantly - it is much more energy efficient than a standard water pump. A 30watt air pump can realistically pump over 20,000 LPH - based on an airlift built out of 110mm pipe, that is 1.70m long and providing there is a good supply of water to the air lift.

It adds air to your pond water.

It can't run dry or burn out like a conventional pump

There are no moving parts to get jammed or broken. At most you'll have to get new diaphragms for your air pump every few years.

It won't get blocked by solids - well within reason.

Its cheap and easy to build.

It can act as a foam fractionator - so if you suffer from foam on your pond surface due to DOCs, this is a good way to remove it.

Its easily scalable - if you need more flow than one can provide, just build more. Two airlifts in an optimal configuration supplied by one 58watt pump can potentially deliver between 40,000-48,000lph!

In the long run, energy prices will go up as we change our energy mix to renewable energy - an air lift will save you £££'s in energy bills, plus having to keep forking out for conventional water pumps.
If the airlift is installed in a tank you can put extra filtration in that tank - anoxic baskets spring to mind!

Cons
Due to how it works, an airlift can't pump water to any height above the pond water level. So can only really be used in a gravity system whereby the water is returned at, or just below water level in the pond.
To ensure sufficient flow, the airlift needs to be around 1.5m - 1.7m tall, so ideally needs to be located in water that is around 1.7m - 2m deep, which unless block built, can be hard to find.

As flow is controlled by air supply, I use an air manifold with valves on to control how much air is delivered to the air lift. This requires very small turns of the valve - but it still works fine. It's just not as good as a digital controller on a variable pump.
It really needs a pond return that is 110mm/4" so can't be easily retrofitted on smaller existing return pipework.
The water needs to be delivered at or just below water level so not ideal for mid water or deep returns.

As draw backs go that's not bad!

So for everyone building or thinking of building a pond using a gravity system - I'd strongly recommend you check out Trace's thread, the youtube video above and airlift.eu - Portal and you'll see that it should really be the go-to way to pump water around a gravity system.

And no I'm not on commission for anyone - I just want to spread the word as so few seem to have heard of them before.

Try it out and see!

And if you are still not convinced after all that, it's really easy to see it work for yourself. Just get a long piece of pipe (ideally 110m pipe that is 1.5m long, but anything that will fit an airstone down it) - hold it vertically in your pond so the top is just above the waters surface and the bottom of the pipe is off the bottom of the pond to allow water to flow in.

Now drop an airstone (on an airline of course) in there and lower it down so its near the bottom.

Now turn your air pump on and providing it's powerful enough - a 40lpm pump should do it - water will start cascading over the top of the pipe at a rate that, if slightly submerged, will be 1,000's of litres an hour.

As you can see from the video on youtube, its great advice on how it works and how to build one. But I found some of the materials are really hard to source in the UK and I don't think my DIY skills are necessarily up to scratch for creating the collector. But I found a way around that. So I'll put up a post about how I built mine shortly.

How I built mine

To power my airlift and a bio unit, I use a Hi Blow 80XP air pump. I got this pump second hand for about £100. I chose this pump as it seems to get good reviews and can handle pumping air to around 2m depth. So the air for my bio and to return water to the pond uses just 58watts on my set up. But any air pump will do providing it can handle pumping to a depth of around 2m. and can provide around 40lpm to each airlift.

In the Youtube video there is a lot of talk of using a collector for the airlift to sit in. I found this too much hardwork. So instead, I installed the airlift into a tall black water storage tank I got from here: https://www.tanks-direct.co.uk/water...n-potable.html.

On the airlift tank, I installed two 110mm radial tank connectors on one side of the tank for the supply from my filters and another one on the other side of the tank for the outlet. Note the outlet has to be either at, or just below the pond water level. The top of my outlet pipe/pond return is about 20cm below the water level but still works fine. Also note the pipe on the pond return should ideally be level.

The airlift itself is 1.5m length of black 110mm waste pipe. With a push fit elbow at the top. I then used 2 x 110mm swept T's connected together to act as vents to allow all bubbles to escape. The open end of the second T is then connected up to the tank connector for the pond returns. Simples!

The two swept T fittings are only there to allow the air to escape. I tried using just one, but had a lot of air bubble up from the pond return in the pond. Having two T's/air vents will almost completely eliminate this. I got all the pipework and fittings from Toolstation - so easily accessible and relatively cheap.

To deliver air to the bottom of the airlift you have two main options.

You either drop an air stone down the air lift and have the air line come up the inside of the airlift and out of the first T/air vent at the top and to your air pump. This is the option Trace took in her thread.


Alternatively you can create a chamber around the bottom of the airlift pipe and within that chamber drill loads of 1/2mm holes to allow the air to enter the airlift as small bubbles.. This is the route I took.

To create the air chamber I struggled to find the larger pipework that the Aquatechnobel used in the video. So to get around this, I used 2 x flexible clay to plastic rubber boots from Toolstation: https://www.toolstation.com/flexible...-to-pvc/p54240

And for the main wall of the air chamber I used a 125mm pressure pipe straight socket from here: https://www.gasandwaterpipelines.co....7/G105125.html

It is quite a tight fit to get the rubber boots over the straight socket. So to help I took the jubilee clips off the fatter end of the rubber boots and then put them in a saucepan of hot water to soften them up, and then with a bit of effort the rubber boots slipped on over each end of the straight socket. Once on, they are firmly on, so won't need the jubilee clips and shouldn't leak any air either. And with this you have an air chamber that just slides on over the air lift pipe.

To create the bubbles in the airlift. You'll need a 1-2mm drill bit and to drill loads of holes into the bottom of the airlift pipe, under where the air chamber will fit.

As you can see from the photos, in the final version, I used a large holesaws to cut out four big holes. This was so the airlift pipe can rest on the bottom of the tank, but still allow water to enter the airlift.

Once you've built this, you then need to cut out (with a hole saw) a hole just big enough for your airline pipe work to enter into the air chamber. I used 1" pressure pipe for this and solvent cemented a 1" elbow into the hole in the air chamber. I recommend testing the size of the holesaw needed for the elbow fitting on a bit of excess pipe, as once you drill into the straight socket, if its not a tight fit then you'll have air leak out.

You then just run the airline pipe (1" pressure) up the outside of the air lift tube (I used pipe clips to keep it in place) and glue a hosetail on the end for your airline from your pump to fit onto.

Having re-read the above, I appreciate it can be hard to follow so see the pics below.

And there you have it, an airlift pump that pumps water for very little upfront and ongoing cost which should help reduce your energy bills. If you managed to get this far well done.

I'd be interested to see what people's thoughts are on this.

Here's the template I used to drill out the air holes to produce the bubbles. I now think that there is no harm in drilling more holes, providing they are covered by the air chamber, more holes should result in less back pressure on the air pump.

And here's the air chamber that I built. This works surprisingly well, the rubber boots are tight on so no jubilee clips or glue needed. And if they break due to wear and tear and cheap and easy to replace. Plus if the holes on the airlift get blocked, the air chamber is removable so an added benefit.

And here it is in use. You can see it produces plenty of foam - outside of the pond. I have none in the pond. I've installed a ball valve between the airlift and pond return so it can be isolated if needs be. But as the return is near the surface (the top is about 20cm under the water's surface) its not the end of the world if one is not installed, as you'll only need to drop the water level in the pond to the bottom of the inlet pipe and jobs a good un.

As you can see to ensure good flow from the air lift, I supply the air lift tank with two 110mm pipes. These come from a bio tank and before that a drum which is fed by a 4" BD pipe and 3" skimmer pipe. So the main restriction on flow on my set up is the drum, which I have no qualms about.

Thanks BCC. I'm glad someone read it lol. Took me long enough to write.

I've seen in your previous posts that you'd considered using airlifts as well. So at least the links are here to source the bits to make an air chamber if you go for it in the future.

Well the info is here now. So at least people can read it if they are interested... and have a few hours spare lol.

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I've seen it work going higher than the level of the pond too, by 4 inches or so. This also has a very good build guide for a very simple and cheap way of doing it. Seems to work very well and the pipes do not look as long as 1.5m either (maybe they are?). Skip to 4:34, the guy likes to ramble on a bit.
https://youtu.be/jsJRc-n0abU

Originally Posted by Alburglar

I've seen it work going higher than the level of the pond too. This also has a very good build guide for a very simple and cheap way of doing it. Seems to work very well and the pipes do not look as long as 1.5m either.

I've seen that too, but the post was so long I didn't want to go into any more detail lol

Not sure if you've seen it, but there's a guy from Hawaii on YouTube who creates airlifts that go to crazy heights, but they seem to deliver sod all water and are a bit, er.. splurty.

When I tested my one out in the pond, I found once it was over around a foot above the pond water level, the flow dropped off very quickly to nothing. But as i undestand it, going for a narrower pipe it can help it work even higher above water level than the 110mm version.

So it's worth experimenting to see what you can achieve.

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I really want to go airlift but haven't got 1.7m to play with. Hopefully I can figure out something with shorter pipes.

Originally Posted by colinley1979

I'm in the planning/building stage of my pond. And I've read good things about air lifts. So I thinkni might as well include them while I'm building the pond. And same some money on the running costs.

I've got a couple of questions that you might be able to answer.

1st can can an airlift be used on a skimmer instead of having an electric pump

2nd is there a maximum length for the horizontal pipe that returns to the pond.

My filters ect will be in my shed that is situated behind my pond. I'll have one return going straight into the pond from the shed. But I want another return on the other side of the pond that is 3 meters away. Is this possible or is it too far for the water to travel

Thanks Colin

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Hi Colin

A gravity fed skimmer can be pumped using an airlift. I have a bottom drain and skimmer (floating weir type) being pumped by 1 airlift (both go into a drum and then bio filter, then to the airlift all via 2 x 110mm pipes).

Im presuming you'll be putting a gravity fed filter of some sort onto the skimmer line. So all you would then need to do is run the pipe from that filter into an airlift tank and then from the airlift back into the pond. To ensure good flow you probably want to have 3" or 4" pipework on this.

There are probably other ways of doing it so you could do away with the airlift tank completely. But I've never tried that so can't comment.

Are thinking of having a dedicated airlift for your skimmer line? If so, then i'm guessing you wont need the bigger flow that is needed for your main filtration. So as BCC has said above, you could probably get away with a slightly shorter airlift (e.g. 1.5m instead of 1.7m) which would mean the tank the airlift sits in won't need to be quite as deep as the one I used. Or you could build it out of smaller pipes.

In terms of the length of the return from air lift to pond - that's a good question and I don't really have an answer for you. But it goes without saying that the longer it is and the more bends and valves there are, the bigger the impact will be on flow.

On my air lift return pipe, it's 4" pressure and about 2m long - which includes 3 x 45° elbows and a double union ball valve - yet I still get decent flow. But the less restrictions you can have the better.

I don't know the size of your pond or intended turn over, but if you need the airlift for your main filters to be operating at peak flow, then I'd suggest if possible having the airlift tank closer to the pond return then it is to the filters. Would you be able to conceal it if you had it behind the back wall of the pond rather than in the shed?

As my airlift tank sits along the backwall of my pond, I dug the hole for the tank at the same time I dug the pond. And I laid a 4" concrete base as the tank i used weighs over 700kgs with water in. So something worth considering for the build.

The other thing I'd say to get peak flow, is make sure you do not undersupply the airlift tank. For example, I have 2 x 110mm pipes from my filters supplying a 720 litre airlift tank which has one 110mm air lift in it.

Hope this makes sense and is helpful. Any more questions fire away.

And good luck with the build.

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Thank you for the for the detailed reply.
My pond will be 3 meters x 3 meters x 1.5 meters so around 13500 litres. I'll have one aerated bottom drain. And a surface skimmer built into the block wall.
I've said before on other threads I'm on a fairly tight budget so trying to build the pond as cheap as possible but also build it correctly. And try and keep running cost as low as possible. Because I'm in the building trade I can get most items at trade price if not free.

Anyway back to how my pond will be built. The. Bottom drain will run to a settlement tank with an evolution aqua answer in it. This will do the vast majority of my mechanical filtration. I'm not sure what I should have after this to catch any fines. Because the answer only filters out up to 150 microns. But I'm planning on having an anoxic filter for my biological filtration. There will be 4" pipes connecting the mechanical and biological filters. My plan then was to put a 90 degree bend and send a 4" pipe down to about 1.8 meters below water level and connect that to an air lift like trace has built. Simple but effective. I've got jebao 100lpm air pump that's 65w and another pump thats 50lpm and that's 40w. I was thinking I could run my bottom drain and 2 airlift with the 100lpm or would it be better to run 3 separate smaller pumps?

My problem start with how I'm going to power the the surface skimmer. And also where I place the inline heater and uv.

I'll try and draw a quick drawing of what I was thinking of and if you could give me any pointers on what would work and what wouldn't. That would be great

Thanks again

Colin

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Originally Posted by Stuffyrat

That's what she said

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Originally Posted by colinley1979

Thank you for the for the detailed reply.
My pond will be 3 meters x 3 meters x 1.5 meters so around 13500 litres. I'll have one aerated bottom drain. And a surface skimmer built into the block wall.
I've said before on other threads I'm on a fairly tight budget so trying to build the pond as cheap as possible but also build it correctly. And try and keep running cost as low as possible. Because I'm in the building trade I can get most items at trade price if not free.

Anyway back to how my pond will be built. The. Bottom drain will run to a settlement tank with an evolution aqua answer in it. This will do the vast majority of my mechanical filtration. I'm not sure what I should have after this to catch any fines. Because the answer only filters out up to 150 microns. But I'm planning on having an anoxic filter for my biological filtration. There will be 4" pipes connecting the mechanical and biological filters. My plan then was to put a 90 degree bend and send a 4" pipe down to about 1.8 meters below water level and connect that to an air lift like trace has built. Simple but effective. I've got jebao 100lpm air pump that's 65w and another pump thats 50lpm and that's 40w. I was thinking I could run my bottom drain and 2 airlift with the 100lpm or would it be better to run 3 separate smaller pumps?

My problem start with how I'm going to power the the surface skimmer. And also where I place the inline heater and uv.

I'll try and draw a quick drawing of what I was thinking of and if you could give me any pointers on what would work and what wouldn't. That would be great

Thanks again

Colin

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That sounds like a good sized pond.

In terms of air pumps, I'd have your bd on a separate pump to the airlifts. You can have your airlifts on one pump and use a manifold with valves on to control the flow to each one. If you want to use your existing ones, I'd say the 60w jobby for the 2 airlifts and the 40w on your bd (hopefully its powerful enough for the depth).

In terms of anoxic filters, maybe consider having them in the air lift tank itself. That would be a very compact solution! In the tank I use I could probably have two stacked up from the bottom. The only issue is how can to lower them in and take them out as it's so deep.

If using heaters and UV these will have to go on before the airlift as neither of these will want any air in them.

For the UV rather than have an inline one I'd suggest an amalgam. They dont restrict flow. And although they're pricey to buy, they are apparently more efficient per wattage than inline uv units. I have a 40w one in my drum (could you drop your one into the answer) and it currently only comes on for 5 hours overnight and was turned off over winter. Plus the bulb lasts (apparently) lasts for 16,000 hours so should last a while especially if not on all the time.

Ive not tried taking traces' approach. But if you did maybe have that setup on your skimmer line and an air lift tank with anoxic baskets in, on your main filtration line.

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