Pond Boss Forums AERATION Systems questions Diffuser area of influence

I'd like to hear some thoughts on this pic

Generally - the deeper we place the diffuser the more time it takes for the bubbles to reach the surface. As the bubbles rise their influecnce of spread becomes wider, greater and stronger. The big variable with this comes in the design of the DIFFUSER. There are numerous designs for diffusers. Few have actually been tested for efficiency, i.e. amount of water movement per cfm of air. One can say anything about how well their design works (highly subjective), but has it been really been tested and proven how it performs?

Another concern is how rapidly will the diffuser pores become clogged and how east is it to clean a clogged diffuser. Diffuser clogging is a whole separate topic and is influenced mostly by water quality and the organisms and silt load in the pond/lake.

Thanks Bill! What do you think about the depths/vs the influenced area in that pic? If we continued that on up, do you think a diffuser at 20' deep could influence 2 acres?

""What do you think about the depths/vs the influenced area in that pic? If we continued that on up, do you think a diffuser at 20' deep could influence 2 acres?" Answer - yes to an extent. The currents may dissipate by the time it reaches the 2 ac area. Amount of influence will be highly dependent on amount of air (cfm) going to the diffuser and size of the diffuser. If the bubble plume is weak when it reaches the surface the distance the currents will extend becomes proportionally less. However this weak bubble plume will be stronger with the diffuser at 20 ft compared to if the same systems and diffuser was located 10 - 14ft deep. How much resistance there is to the spread of the bubble plume is highly dependent on water temperature. Less resistance to mixing as the water temperature drops toward 39F at the temp water mixes easiest. Thus the influence area becomes greater at 39F and less as the water increases in temp. Wind direction and speed amount have some influence.

I am not a big 'fan' of the diffuser design picture above. Any proof data how well it mixes water? The design makes ganged or connected or multiple head diffusers rather difficult. Many diffusers are built unique but do not perform better than others especially if there are no supporting tested, measured, or comparative data. In most cases a poorly designed diffuser is usually better than no diffuser.

Thanks again Bill. I should say that I am currently using Vertex diffusers and have no plans on changing. Just doing some reading and came across that pic. When I asked the question, I meant for diffusers in general. I did not realize there would be quite that many variables. I should have known, it depends. Lol

Vertex is one company that has methodically tested and documented the water lifting rates of their diffusers. This is to be commended and sets a standard for all to follow.

Something that many people may not think about or know (but SCUBA divers have to be well aware of) is how air released at depth expands.

A little background first. The distance from outter space to sea level is our atmosphere. At sea level the "weight" of this air is just under 15# per square inch. When we measure tire pressures or any other air pressure we do not count this pressure. Instead we start the pressure scale at zero, but if it was measured in outter space the pressure we measure at sea level would be almost 15 psi more at sea level than outter space (when measured at ground level we measure negative pressure on a scale as vacuum). So at sea level we are breathing air and the surrounding air is at slightly less than 15 PSI.

Water is denser than air. It weighs more than air. So as we decend in water the pressure rises more rapidly than as we decend in air. In fact decending about 33 feet in water has the same effect as decending from outter space to sea level in air. So one atmosphere of air pressure is the equivelant to a depth of 33 feet in water, or one atmosphere of water for every 33' of depth. This is why it takes a compressor that will develop about 15 psi to overcome the head pressure of water if a hose or diffuser is submerged to a depth of 33 feet. If your compressor will only develop 10 psi, it will stop flowing air as the hose decends down to about 22 feet.

Ok, that was long winded. Why does it matter concerning diffusers? The bubbles themselves do not infuse that much O2 into the water. The bubbles push the water to the surface so the air/water interface at the surface can do the majority of the work of putting O2 into the water.

Here is where all the long winded part explained above comes into play. If you were to fill a toy balloon fully with air at a depth of 33 feet, tie it off and release it, it would burst before it reached the surface. The one atmosphere of water pressure (almost 15 psi) it took to fill the balloon at 33 feet (two atmospheres of pressure) would expand to two atmospheres in size and burst the balloon as it rises to meet the surface pressure of one atmosphere.

So bubbles released at depth expand as the water head pressure decreases as the bubble rises. The bubbles get bigger. Put a tiny it of air in a balloon at 100 feet depth and it will be fully inflated when it reaches the surface. This is why divers never hold their breath when accending. The compressed air we are breathing at depth expands in the tiny air passages in our lungs and bursts. With a full breath and rising holding ones breath it can happen in as little as a four feet and is called air embolism. It is a bad and often leathal thing.

So how does this apply to pond aeration? Well first off it tells us we need a compressor that will operate at adequate pressure for the depth we place the diffusers. But it also tells us that the deeper the diffuser, the greater the expansion of the bubbles as they rise to the surface, so with greater surface area the bubbles will push more water. That is why a diffuser placed at a deeper depth (assuming the same cfm of air delivery) will move more gallons per hour than a shallower placement. The bubbles are released under greater pressure therefore have a greater expansive capability therefore a greater water movement capability.

WHEW! Anyone still awake.

I'm no expert on this, but I am a scuba diver so have to understand what happens when breathing air at depth. Same applies to air being released from a diffuser at depth.

Snrub - That was a very good lesson for releasing air underwater. Also keep in mind the bubbles not only expand as they rise they spread out into a larger ascending mass or plume of bubbles. I will find a place to put this air lesson into the aeration section of the archives.

Thanks Snrub! Very interesting stuff.

so a followup question would be, if your pond was being built and you were shooting for a depth of 10' or so. Would it be wise to dig a crater in the middle of the deep part maybe 15' wide and another 6'-8' deep? Then put the diffuser down at 16-17' deep? That way you don't have a pond that is that deep all over (added costs), but the diffuser takes advantage of extra depth to produce bigger bubbles by the time they hit the surface and you get a bigger plume as the bubbles have more height to ascend?

You could incorporate this diffuser crater into ponds best at time of new construction.

I think that unless the pond bottom is made of a material that will not slough off and/or slide around, the crater will fill up rapidly from inorganic sediment. I've seen this in ponds with a sandy bottom. Within one year after being dug, a pond that had a wide deep trench down the center was less than a foot deeper than the rest of the pond in that area.

Plus, how would you compact that area to ensure that the pond didn't leak in that area?

Great explanation snrub!!

Thank you snrub... great read!

Great information as I continue to learn and work toward aeration in my pond.

I agree with esshup. A steep sided trench even built in clay bottom quickly gathers sediment into the bottom of the "funnel". The steep uncompacted sides of the trench does tend to slough. If a bottom center trench is built the sides should be sloped at least 2:1 and compacted to minimize sloughing.

Sometimes a deep hole like that will lead to a seep due to increased pressure.

Keep in mind Canyoncreek, you cant get something for nothing. A deeper hole means increased pressure to pump air down. This could mean several different things depending on the pump selection. It could cause reduced cfm output of the pump. So although you are making larger rising bubbles, you may be making less of them. Or it could relate to a higher electricity cost to operate.

Linear motor pumps are very sensative to back pressure (depth) and performance drops off quickly as the pressure rises. Vane pumps are less sensative but still loose efficiency as back pressure increases. But they efficiently put out large volumes of air when used for the depths they are designed for. Rocking piston compressors see the least reduction in performance with depth so are more suited for deeper BOW's but they are not the most efficient from an electrical usage standpoint when used for shallower depths.

All of the above simply means you need to pick the pump style best suited for the depth you plan to operate it at. It is a matter of choosing the right tool for the job.

Which points out the need to use the advice of some of the pro's and long time users of aeration systems to see which systems perform best in different applications. And I am definitely not that person. I understand the theory behind the designs pretty well, but am very short on actual experience using different systems.

Thanks Bill and snrub, I had an expert size my diffuser and setup (Sue Cruz, I hope she is still in business and helping pond boss members as she has been quiet on the forums for a while).

I think for me the first priority for better 'plume' is to keep the pond at full pool. There is a noticeable difference in plume performance if the pond is down even a foot. The other thing is to get in there and clean the diffuser head more than once in the spring. The suspended clay and whatever else forms a tight skin on that diffuser gets pretty thick pretty fast. I find it easier to pull the diffuser up while it is on (easier to find it in the middle of the pond too When I gently rub with my finger pads (not nails) while the diffuser is flexed and domed up with air it tends to dislodge eaiser and the air bubbles and repeated dunking and rubbing cleans it up in a hurry.

I have cleaned them both in the water (both breath holding and SCUBA) and out. When in the water I either use my hand or preferably my hand with a glove on. I also clean them with the air applied. You can instantly see the improved air flow under water if you have a mask on and if enough light penetrates down to depth to see. The white bubbles show up pretty well even if it seems pitch dark when I go down.

Which reminds me, I never got around to cleaning mine last fall when the water was still warm so it looks like donning a wetsuit is in order this spring. Brrrrr. Cold and dark water is not all that inviting. I may just pull them up to the boat instead.

Hey guys!! I'm still here! I'm sorry I haven't posted in a while ~ I just missed Ted so much after he passed that I had a hard time getting back into the forum. Thank you for the shout outs! This is a great thread! I'm with Cody ~ I am not a fan either of the old depth/diffuser chart ~ it's basically there sell a system with out the personal, scientific or customized recommendation. There are so many factors involved in sizing an aeration system that you just can't put it into such a simple diagram. Real science, real people and their goals, and real ponds... anyway, I think you guys all know your stuff and are doing great on the aeration front! I'm always an email away! I'll try to make some time to snoop around and pipe in on some of these topics that I've missed!! I hope to see a lot of you at the conference in October!!

Sue - Very good to hear from you. Don't continue to be a stranger.

Great to see you posting !!!