Air Lift for Under Gravel Filter System

The place to discuss the regular pressure chamber Airlift.
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JohnGJ
Posts: 2
Joined: 01 Dec 2020, 20:30

Air Lift for Under Gravel Filter System

Post by JohnGJ »

I am designing an under gravel filter and want to use a pressure chamber airlift to move the water. It will work just like an aquarium with bubblers on an under gravel filter - just much larger. I understand the basic concept but I have a many questions. I think you as a group are way ahead of us in the US on how to best use this technology on a larger scale.
1- If I use a 6” (152 mm) lift pipe and reduce to a 3” (76 MM) PVC under the gravel (these will have 3/8” (10 mm) holes drilled every 175 mm in it to pull water down through the 6” (150 mm) of 3/4” - 1” (20-25 MM) gravel layer).
1a- Will reducing from a 150 mm lift pipe to a smaller under gravel pipe create a higher velocity of flow in the smaller pipe like a smaller hose opening does on a garden hose - but in reverse?
2- Does using a larger lift pipe - say 150 mm instead of 100 mm create a great deal more lift in total volume of water moved? Does it take a lot more air to power a 150 mm over a 100 mm pipe - is it worth it? How much more?
3- Pressure chamber question. On the videos it looks like the pressure chamber is very “thin” - 6-7 mm. Is it important that the chamber is that small or could I use a 100 mm lift tube and a 150 mm chamber?
4- do yo have a formula for how many holes and size of holes for the pressure chamber to tube holes?
5- how many holes/liter of air flow? Is there a formula?
6- Air Lines: how far can I effectively run an air line? The pond plan is quite large - around 45,000 liters. There is a small building that I want to put my air pumps in and it is about 10 M from the lower end of the pond. I think some of the air lines might be as long as 30-40 meters. Will I lose air pressure over that distance? The lift tubes will be almost 2 M deep.
6a- I am trying to produce about 40,000 liter/hr total flow through the under gravel system and would like to do it through two lift tubes.
7- There are a few people here doing under gravel filters in ponds and they seem quite effective. This pond will also have a large bog/wetland filter - about 3 M x 5 M and 1.5 M deep. I know on gentleman outside of Chicago that has a 27 year old under gravel filter set up that has run trouble free for that entire time. They are all running on traditional pumps that are 400-600 Watt motors. The idea of running the same type of flow (it might take 2-4 20 Watt air pumps) for a small fraction of the cost is very attractive. I plan on putting a diverted valve in at ground level for winter aeration at a shallow depth that will turn off the lift for the winter.
I will be grateful for any help and advice you can offer. I appreciate your ideas. I would love more videos in English :).
Thank you for your help
John
*** One last question. In the videos it looks like everyone builds these with an two air release pipes/vents prior to the outflow of the water. What is the reason for this? Just bubble reduction in the pond? Or is there a flow change?
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Pssymon
Posts: 200
Joined: 11 Dec 2015, 00:12
Location: The Netherlands

Re: Air Lift for Under Gravel Filter System

Post by Pssymon »

Hi,

I'll answer the best I can in the quote below.
For me to better understand the design, a drawing would be helpful.
JohnGJ wrote: 13 Dec 2020, 16:50 I am designing an under gravel filter and want to use a pressure chamber airlift to move the water. It will work just like an aquarium with bubblers on an under gravel filter - just much larger. I understand the basic concept but I have a many questions. I think you as a group are way ahead of us in the US on how to best use this technology on a larger scale.

1- If I use a 6” (152 mm) lift pipe and reduce to a 3” (76 MM) PVC under the gravel (these will have 3/8” (10 mm) holes drilled every 175 mm in it to pull water down through the 6” (150 mm) of 3/4” - 1” (20-25 MM) gravel layer).
I think I understand what you are trying to do, but it's very far from what we have experience with. Technically this can work but I don't know what the effect will be on your flow. Since you connect a 76mm pipe underneath your 150mm pressure chamber, your inlet is effectively only 76mm. No matter how many holes are in that 76mm pipe.

1a- Will reducing from a 150 mm lift pipe to a smaller under gravel pipe create a higher velocity of flow in the smaller pipe like a smaller hose opening does on a garden hose - but in reverse?
It probably will, and it will, as I said, make your inlet 76mm which will probably limit your flow (if I'm understanding your idea correctly).

2- Does using a larger lift pipe - say 150 mm instead of 100 mm create a great deal more lift in total volume of water moved? Does it take a lot more air to power a 150 mm over a 100 mm pipe - is it worth it? How much more?
150mm requires significantly more power to run. Even in the optimised builds they have a worse efficiency. I would only advise to build bigger airlifts when there is limited room and really high flow rates are needed.

3- Pressure chamber question. On the videos it looks like the pressure chamber is very “thin” - 6-7 mm. Is it important that the chamber is that small or could I use a 100 mm lift tube and a 150 mm chamber?
As far as I know this does not matter, as it only takes a small amount of time for the chamber pressure to build up to its constant value. The number and size of holes is the deciding factor here (and the air-tightness of the chamber).

4- do yo have a formula for how many holes and size of holes for the pressure chamber to tube holes?
We do not. For this info please refer to our build guide on Youtube:


Someone did post a link to a calculator on the forum. I just checked and that link is not working anymore...


5- how many holes/liter of air flow? Is there a formula?
We still have to test this ourselves. We do not have a formula. The best advice I can give is to stick to what we have tested and built and carefully add holes as you try bigger pumps. For test results please have a look at this topic:
viewtopic.php?f=118&t=15803


6- Air Lines: how far can I effectively run an air line? The pond plan is quite large - around 45,000 liters. There is a small building that I want to put my air pumps in and it is about 10 M from the lower end of the pond. I think some of the air lines might be as long as 30-40 meters. Will I lose air pressure over that distance? The lift tubes will be almost 2 M deep.
I can't tell you with absolute certainty, but I would be surprised if that would be a problem.

6a- I am trying to produce about 40,000 liter/hr total flow through the under gravel system and would like to do it through two lift tubes.
20.000 liters per hour could be achievable depending on the drag in your system and what pumps you use. Don't expect to hit the numbers we have in our tests as these are measured without drag. I would get bigger pumps than we used to make up the difference. If you really want to be energy efficient I would advise you to simply use our designs and pump combo (now you would probably need Secoh JDK(30) pumps) and use 3 airlifts instead of two. If you have to use two, use JDK 50's for example.

7- There are a few people here doing under gravel filters in ponds and they seem quite effective. This pond will also have a large bog/wetland filter - about 3 M x 5 M and 1.5 M deep. I know on gentleman outside of Chicago that has a 27 year old under gravel filter set up that has run trouble free for that entire time. They are all running on traditional pumps that are 400-600 Watt motors. The idea of running the same type of flow (it might take 2-4 20 Watt air pumps) for a small fraction of the cost is very attractive. I plan on putting a diverted valve in at ground level for winter aeration at a shallow depth that will turn off the lift for the winter.
I will be grateful for any help and advice you can offer. I appreciate your ideas. I would love more videos in English :).

More videos are definitely planned but things have not worked out as I expected, causing massive delays. I'm hopeful we will have more to share this year.

Thank you for your help
John
*** One last question. In the videos it looks like everyone builds these with an two air release pipes/vents prior to the outflow of the water. What is the reason for this? Just bubble reduction in the pond? Or is there a flow change?

Those T-pieces are needed to let the air that carries the water upwards escape. The first opening is absolutely necessary as the generated air needs to escape, if it doesn't it will cause a lot of drag. The second opening can be used for protein skimming. This is not easily achieved though and requires fine tuning. It's considered to be more of a bonus feature.
JohnGJ
Posts: 2
Joined: 01 Dec 2020, 20:30

Re: Air Lift for Under Gravel Filter System

Post by JohnGJ »

Thank you so much for your time n replying! I love what you guys are doing. Airlifts for pond have not really caught on much in the US - we are just behind :D
** More in English please - I fee like I a missing so much!
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