Airlift Discharge 50cm below water line?

In depth subjects relating to Airlift.
Post Reply
martins
Posts: 3
Joined: 31 Jan 2017, 04:25
Location: Shanghai

Airlift Discharge 50cm below water line?

Post by martins »

Hi
I am currently in the planning stage for a 5000 L fish pond (would like to try small scale fish farming for the 1st time) + growing beds, and then from a Collection Tank I was thinking about whether I could use an Airlift Pump and discharge the water back into the main fish tank with no Discharge Head. The catch would be, that I would like to discharge back into the main fish tank at a depth of 50cm +/-. The water pressure in the main tank at this level would be 0.7 psi, would the airlift discharge flow be enough to overcome this?

I am a complete newbie, but I'd like to try and get this right from the very start and it would be good to use an airlift.

Thanks in advance for any advice you might have!

Martin

54992

User avatar
Pssymon
Posts: 175
Joined: 11 Dec 2015, 00:12
Location: The Netherlands

Re: Airlift Discharge 50cm below water line?

Post by Pssymon »

Hello,

I'm pretty sure returning far below water level is no problem. The only problem should be returning above water level.
I will check to make sure.
The water pressure in the main pond or tank should not matter, as long as your transits can handle the flow the Airlift provides. If not, your setup will be inefficient.
I think I understand your design, but why do you want to return 50cm lower? And where will your filters be situated?

martins
Posts: 3
Joined: 31 Jan 2017, 04:25
Location: Shanghai

Re: Airlift Discharge 50cm below water line?

Post by martins »

Thanks so much! Would be great if this is confirmed, I would then change my design

1. Filters placement? : I'm going to put them in between the Pond and the Growing Beds (I didn't put them in this diagram), should have a mechanical filter and a biofilter filled with K1, and then gravity feeding the Growing Beds.

2. Why do you want to return 50cm lower? : I want to use Gravity (and absolutely no electric pumps at all) and the water flow will be (1) Pond --> (2) Mechanical Filtration --> (3) Biofilter --> (4) Last Chamber (i) AirLift back to Fish Pond (ii) Gravity drain to Growing Beds --> (5) Growing Beds Drainage --> (6) Collection Tank/Sump tank.

Hence, in steps 4 to 6, I will drop at least 50cm. I'd like to get that water back into the Main Pond. Ideally without lifting it up 50cm of Head (this was my original plan to use a small pump), so I was thinking could I just return directly into the Pond below water level.

I won't have enough Grow Beds to support the entire Pond hence why I will still do Filtration and only have some of the water diverted to grow Vegetables. If I can return far below the water line, then I might also just remove step (4)(i) the Airlift, and just have part of the water go to growing beds, and the rest go directly to the Collection tank and then just have the 1 airlift to return the water to the tank (maybe it will end up 60-80cm below the water line)

User avatar
Pssymon
Posts: 175
Joined: 11 Dec 2015, 00:12
Location: The Netherlands

Re: Airlift Discharge 50cm below water line?

Post by Pssymon »

Good day,

Apologies for replying quite late, I was ill last week and after that I was busy working.
I did discuss this with Marc before though.

In your current drawing this will not work. If taken literally, your setup would look something like this:

Image

Which is impossible as all water containing containers must have an equal level for this to work.
If we adjust for this we get a drawing that will be possible, but then the Airlift outlet is near the water level.
I thought you could just place the entire Airlift lower without problems. But Marc mentioned to me that the pressure will rise to a level that most airpumps will not be able to overcome.
And looking back, that makes sense, as you're actually doing the same thing as when you extend the rising pipe, which has a huge effect on your yield.

If returning lower in the pond is really important for some reason, this is how you can achieve it:

Image

It is quite simple, after the outlet you place a T-piece (as you would in most cases anyway, to let excess air escape).
At this point the Air will be able to escape from the Airlift.
Then you have to add a 90 degree bend downwards, and a length of pipe depending on how deep you need to go.
Lastly, add another 90 degree bend and connect it to the pond.

The simple drawing above shows how this works, the Airlift pumps heavily oxygenated water upwards, then most of the air that would otherwise be trapped will be able to escape.
Next, the water that contains much less air will be able to flow towards the pond.

I hope this helps you, I would suggest doing it as I've drawn in the last image if you want to have your Airlift outlet low in the pond, if not, you can just connect to your pond at the normal height.

Please note that the way the filter and Airlift are placed is optimised to have a better understanding from a side view. In a real life application you would build all of this next to the longest side of the pond so your Airlift outlet will be as short as possible.

Frank
Posts: 52
Joined: 24 Apr 2016, 22:04
Location: Ceylon

Re: Airlift Discharge 50cm below water line?

Post by Frank »

The "90 degree bend downwards" will reduce performcance compared to usual airlifts, right?

User avatar
Pssymon
Posts: 175
Joined: 11 Dec 2015, 00:12
Location: The Netherlands

Re: Airlift Discharge 50cm below water line?

Post by Pssymon »

Yes, you are correct Frank.
Any additional bend or extra length of pipe will lower efficiency. By how much, I don't know exactly.

Frank
Posts: 52
Joined: 24 Apr 2016, 22:04
Location: Ceylon

Re: Airlift Discharge 50cm below water line?

Post by Frank »

Thanks :good:

martins
Posts: 3
Joined: 31 Jan 2017, 04:25
Location: Shanghai

Re: Airlift Discharge 50cm below water line?

Post by martins »

Thanks so much for the help. And also apologies for the late response. I will use the airlift but probably in the more convential way

User avatar
Pssymon
Posts: 175
Joined: 11 Dec 2015, 00:12
Location: The Netherlands

Re: Airlift Discharge 50cm below water line?

Post by Pssymon »

Good luck with it! If you want you can always share your progress here so others may benefit.
I will soon update Gino's build topic (Airlift with drumfilter pond build). If you keep an eye on that topic it will show many professional techniques and some simple tips for an Airlift driven pond build as well.
I'm also working on another build topic, so that will be online very shortly as well.

Rich Palmisano
Posts: 35
Joined: 22 Aug 2018, 18:38
Location: Jacksonville, Florida

Re: Airlift Discharge 50cm below water line?

Post by Rich Palmisano »

My understanding is (correct me if I'm wrong) that this pump relies on equalization of the water level to be most effective.

User avatar
Pssymon
Posts: 175
Joined: 11 Dec 2015, 00:12
Location: The Netherlands

Re: Airlift Discharge 50cm below water line?

Post by Pssymon »

That is correct. The base rules for this concept to work at maximum performance and efficiency are:

- No discharge head at any point in the entire system
- Large transits which will allow for enough flow
- A filter that has the least amount of restriction in terms of filter media
- A proper air pump that can provide pressure at 170-180cm deep
- Build the Airlift to the correct length for the pump you will use

Rich Palmisano
Posts: 35
Joined: 22 Aug 2018, 18:38
Location: Jacksonville, Florida

Re: Airlift Discharge 50cm below water line?

Post by Rich Palmisano »

The main issue I see with putting the pump below water level is service. You won't be able to access the pump without losing water above the pump. This would work in practice but if you had an issue with air connection you'd be draining the system to access it. I am assuming the pump well is sealed, as it would have to be, or that "water seeking it's own level" thing would have water gushing from the pump well.

Upon further thought, you could have ball valves at either end of the pump well to close flow from the return and to the inlet of the pond. That would stop flow to the pump well, through a the top seal, allowing access without water flowing out of the system.

Hmmm, this could work, but again as stated, you would need to be sure that the air pump is robust enough. Total head would be the well depth to the top of the pond. A quick calculation for a 2.9 PSI/40 liter pump says you can go 6.7 feet deep (1 atm = 14.69 psi = 33.9 ft of water). Not sure how much air is going to move at that depth though. Also, I'd venture to guess that the connection pipes would need to be large to allow flow.
Last edited by Rich Palmisano on 05 Sep 2018, 14:33, edited 5 times in total.

Rich Palmisano
Posts: 35
Joined: 22 Aug 2018, 18:38
Location: Jacksonville, Florida

Re: Airlift Discharge 50cm below water line?

Post by Rich Palmisano »

https://photos.app.goo.gl/pqXsgR9hum49R1BN7" onclick="window.open(this.href);return false;


Here's a diagram of my thoughts... in hindsight, the grow bed should be at the same level as the pond, otherwise the pond would continue to flow to the grow bed at least until the water level was below the pond outlet.

Post Reply