Pond Boss Forums AERATION Systems questions long distance air lines

I am in the process of planning an aeration system for a 40 acre lake in Ontario, Canada, which is prone to winter kill. The person at the pond supply store is recomending 2-1hp compressors for the lake, one for each of the two deep basins, and 5 or 6 air stones for each compressor. The run from the compressor to the area of the lake where the diffusers are located is over a thousand feet. Here are my questions:

1. what size tubing to use?
2. how to go about braching the tubing to accomodate the 5 airstones? (i.e. can you branch further down the line, or do you have to brach at the compressor?)

Hi James -
There are several points you need to keep in mind when determining which aeration system to use for this 40 acre lake.
Be aware of maximum PSI on the rotary vane compressors. Most can't run over 10 or 15 PSI which can be very limiting when it comes to long tubing runs, deep diffuser placements and higher altitudes. Instead you should look for a system powered by piston compressors. They have a max psi of 20 or if needed 35. Pistons also are easier to maintain than the rotary vanes. With the right type of diffusers you will have no problem running tubing thousands of feet.
Which brings me to the airstones. Please look into membrane type diffusers. These are self cleaning and much more efficient. Airstones will clog over time and require reqular acid baths. Membrane diffusers are self cleaning and do not ever need to be removed from the bottom of the pond.
You should make sure that you are properly aerating this pond. A system that does not have enough 'lift' will only result in mixing the bad bottom water with the good water with out ever pushing the bottom water all the way to the surface where it can expel built up gases and absorb oxygen. This will result in lowered O2 through out the water column and increased CO2 which is a very important nutrient for algae.
Look into Vertex aeration systems. They can assist you with accurately sizing this lake and determining how many diffusers you need and where they should be located to prevent future winter fish kills.
Do a search on this site to read more information on aeration systems and preventing winter fish kill.

James, S-rat is right on the money. I would suggest you try the aerial mapping link on my "Getting Started" section ( see web page) which will get you a free aerial map and system sizing spec sheet for this lake from Vertex Water Features. You may also want to call Sue Cruz with Vertex about any specific concerns you may have for this project. The toll free is 800-432-4302 Good Luck Ted

The deepest air stone will be in 20 feet of water. They are suggesting 1 hp rotary vane compressors and 1 inch line approx. 1000 feet long, then branching into 3/8inch lines to feed 6 air stones. Any thoughts? How many psi will I need to accomplish this?

James, my 2 cents, being an engineer I would suggest you rely on some expert advise from those who design these systems or you can get into trouble fast. Case in point is the pressure required. I agree with a previous reply that you need something with higher pressure capability than a vane pump. The water depth alone will require 9 psi to get the air to the bottom. And your correct that your line needs to be sized correctly or you'll add a bunch more resistance. If you use 1 inch line 1000 feet long and assuming about 10 cfm from pump you would lose another 2 psi (more if higher cfm). That means just to get the air to the diffusers you'll need 11 psi, not accounting for check valves, diffusers, and losses in elbows or bends in pipe. This tells me that if your source is suggesting a vane pump with 1 inch line they are cutting it pretty close. Find a better source. Here's a web site that has data on pressure loss in pipe and fittings for reference. http://www.aquatext.com/tables/frict-air.htm#CFM%20and%20PSI%20%20Table. I'm not sure I agree with the poster who states that the membrane diffusers are more efficient. I haven't seen one that is more efficient than air stones at dissolving air into the water. There is a world of difference read this (http://www.aquaticeco.com/index.cfm/fuseaction/popup.techTalkDetail/ttid/49). But he is correct that they are relatively maintenance free. Just keep in mind that in order to get the same amount of air dissolved into the water you will need more cfm which can tranlate into 3 times more power and higher electic bills. I would argue that for a large lake you really want to maximize efficiency. Over the long run this might far outweigh the occasional replacement of air stones. Air stone life depends on your water chemistry and whether you have a good air filter. Also read this about membrane versus air stones, also give some good advice on cleaning.(http://www.aquaticeco.com/index.cfm/fuseaction/popup.techTalkDetail/ttid/78)

James,

At that length and depth with 3/4" lines, I think your only going to see about 25-28% output volume vs. input volume without considering the loss at each airstone.

Chip