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Diffuser heads
#515495 01/05/20 11:57 PM
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I am looking into purchasing a system and have seen systems with two (dual) diffuser heads per line and systems with one diffuser head per line. Any opinions on why one set up would be better than the other? Thanks in advance.

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Re: Diffuser heads
TucknDucks #515502 01/06/20 01:22 AM
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The volume of water moved to the surface is different with the two different air stations.


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Re: Diffuser heads
TucknDucks #515527 01/06/20 10:40 PM
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esshup, thanks for the reply. I just want to clarify. Are you saying if I only have 1 airline coming from the compressor but it has a dual diffuser head (tandem within 1 foot of each other), it will move more water than one airline with a single diffuser head?

And if it does move more water then do I need a more powerful compressor to run the tandem head?

Thanks

Re: Diffuser heads
TucknDucks #515558 01/08/20 07:21 AM
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A diffuser will have a CFM rating range. It will operate most efficiently within that range. Too little air and it will not perform as well and too much might over stretch and damage it.

So the first order of business is see what CFM the pump puts out at the depth you will be operating.

If we assume the pump has the capacity to deliver air that is within the range of either a single OR double diffuser, then the double will likely do a slightly more efficient job of moving water. Probably not a huge amount better, but some better. At least one reason being the bubbles seperated slightly in columns tend to grab more water between them as they go up.

That is what you are doing with aereation. Moving water from the bottom of the pond to the top where is can take on O2 at the air/surface interface. So moving water is the key and the bubbles are what moves the water up.

So if you have a pump that is getting toward the upper limit of what a single diffuser will handle, might want to go double. If you are scraping the bottom of the barrel for CFM barely making it into the range of a double, might be better to stick with a single.

The whole thing is, figure out how much air and turnover you think you need, then size the pump and diffusers to that need. It is as much of an art as it is a science.

No expert here. Just what I have learned from the big boys.

John

Last edited by snrub; 01/08/20 07:23 AM.

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Re: Diffuser heads
TucknDucks #515560 01/08/20 11:37 AM
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Suggestions above are good.

Ideally you want the dual or multiple diffuser heads (membranes or stones) close enough together so the rising columns of water quickly merge together that produce more upwelling than if they were working separately. Manufactured company systems incorporate this philosophy; hopefully all by testing. Merged columns work together(team) to gather more rising water. Thus a combined rising column moves more water than two single rising columns. This assumes that in each scenario all heads receive the same volume of air(cfm).

Also, if you double the cfm(2cfm) to one diffuser instead of splitting 2cfm into two diffusers (1 manifold) the dual manifold will move more water because the single diffuser(2cfm) has the rubber membrane pores stretched further open that creates larger bubbles. With any cfm, smaller bubbles more water than larger bubbles mainly because the smaller bubbles collectively have more surface area that creates more upward moving water. Each type of diffuser has an optimum air flow for optimum efficiency.

RULE: The smaller you make the bubbles (same cfm) and more bubbles you make - the more water you move. Example: A 'large' 20mm bubble has the surf area of 12.5cmsq and a vol of 4.19cubic cm. 296 3mm bubbles can be made from this 'large" bubble. These 296 bubbles have a total surface area 83.6cmsq which is 6.6X more surface area of our 'large' bubble. In theory we move around 6.6 times more water with the 3mm bubbles than 20mm bubbles; all assuming same cfm. IMO the best membrane diffusers are designed to make 1mm bubbles at optimum air flow volume.

Last edited by Bill Cody; 01/08/20 11:47 AM.

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Re: Diffuser heads
TucknDucks #515575 01/08/20 05:43 PM
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Here is an old thread that might be useful.

aeration turnover rate


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Re: Diffuser heads
snrub #515576 01/08/20 05:53 PM
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Another thread. About 5 or 6 posts down the page I have some pictures of DUAL Matala diffusers. I use 2 disks in the main 3 acre pond and a single in each of the 1/20th acre forage pond and 1/10th acre sediment pond .

http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=388406

When I was driving each dual with an individual diaphragm pump on occasion one disk would stick shut and only be putting air out one disk. I was at the low end of CFM specs.

When I switched to a big vane pump I now drive all the diffusers, 3 doubles and 2 singles for a total of 8 disks. I have not had that issue since.

A discussion of some of this in that thread.

Just an FYI.

I think Vertex is the preferred brand of diffuser here on PBF, but the Matalas have seemed to do the job. Don't really know if something else would have been better.

Last edited by snrub; 01/08/20 10:09 PM.

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Re: Diffuser heads
snrub #515577 01/08/20 06:03 PM
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Here is an old thread about depth of water and aeration air pressure.

pressure at depth


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Re: Diffuser heads
TucknDucks #515587 01/08/20 09:16 PM
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Originally Posted By: TucknDucks
esshup, thanks for the reply. I just want to clarify. Are you saying if I only have 1 airline coming from the compressor but it has a dual diffuser head (tandem within 1 foot of each other), it will move more water than one airline with a single diffuser head?

Yes, 2 diffusers will move more water than 1 diffuser. Now without testing the GPM moved to the surface, how far or close they are spaced will make a difference too. Putting them at the correct spacing will move more water to the surface than 2 single heads. How far apart? I can't answer that question, I go by the chart that Vertex published years ago.


And if it does move more water then do I need a more powerful compressor to run the tandem head?

Maybe but most likely yes. I can only go by the Vertex diffuser disks, I have that information memorized. They need between 0.5 CFM (minimum) and 1.25 CFM (maximum) They will handle more CFM, but the slits will become larger due to the increased CFM and they will become more inefficient due to the larger bubble size. Now when you calculate the CFM, you have to use the compressor mfg's CFM/pressure chart - for every 1' water depth that the diffuser disk has above it you will see approximately 0.5 psi backpressure on the compressor

Thanks

Last edited by esshup; 01/08/20 09:18 PM.

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Re: Diffuser heads
TucknDucks #515606 01/09/20 12:12 PM
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If you are seeing 2 separate boils at the surface the disks are definitely too far apart. I like to keep disks on my manifolds almost touching maybe no more than 1" apart or touching so I know the two water columns conjoin ASAP. The deep the diffuser the more water that will end up in the final flow at the surface.


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Re: Diffuser heads
TucknDucks #515618 01/10/20 09:51 AM
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Bill I'm curious. If closer spacing is better, then why does Vertex build their 2 diffuser systems with the disks purposely spaced quite a ways apart? I notice they have a shallow pond 2 diffuser setup where the disks are spaced a little more closely together than their 'standard' setup but even on the shallow water setup they are no way near 'almost touching' like you recommend.

Re: Diffuser heads
TucknDucks #515623 01/10/20 03:13 PM
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Vertex has their way of doing the membrane spacing. They more than any other Aeration company except maybe Aquatic Ecosystems Pentair have done fairly extensive underwater diffuser testing. Vertex after testing probably decided that two separate rising water columns that merge together at a opportune time (depth) results in optimum flow. My concern is how much does water depth variable affect all this standard spacing rationale?

Evidently Vertex concluded the wider separation of disks suits their sales philosophy. I do it the way my knowledge and common sense about the whole aeration concept suggests. The difference between the two concepts may not end up being a mathematically significant difference. I have never heard a good reason from anyone why wider spacing of diffusers is most beneficial to achieve the most efficient upwelling flow. Too little published good underwater testing has been done for the topic. I have yet to figure out an easy way to accurately measure the upwelling flow of a diffuser assembly. Although I have done dye testing with diffusers.

Watch some aeration underwater bubble patterns and plumes of various membrane disk arrangements. Then you decide for yourself.

Last edited by Bill Cody; 01/10/20 07:35 PM.

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Re: Diffuser heads
TucknDucks #515633 01/11/20 06:56 AM
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snrub, like you I have nothing to compare since I started with Kasco Robust air 4 yrs ago. At that time I had a veterinarian that did all my vet stuff for over 20 yrs (now retired). On one visit he told me his son was the rep for Kasco. In doing a little research I saw their charts comparing 7 other companies diffusers. Like most any business advertisements they boasted of moving more than 100gpm over Vertex @ 6.5' depth, @ 1.5cfm. They also measured 2, 2.5 and maybe at 3cfm. And a lower pump pressure. Each diffusers uses two U shaped tubes and looks like two separated but blended bubble areas at the surface. At that time I think they said the were the leader in market share. And so I gave a call to Ken Rust who is located in Baton Rouge La. He came up to the pond and did a depth survey and made recommendations for the six diffuser station system and with two half hp pumps and where to place them. If memory serves me I am moving air around 2200'. And was cheaper cost than the Vertex at that time.

Today, looking back I had to rebuild the pumps in year 3 and I am the worst DIY guy you most likely will run across so it's fairly simple job if I can do it. My only complaint was they disturbed my pond bottom around the diffuser head so I had to move them off the bottom of the pond where they now set on platform that is 18" off bottom. And they are an advertiser here on the Forum. But again, I have no personal comparison with any others.

Last edited by TGW1; 01/11/20 07:12 AM.

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Re: Diffuser heads
TGW1 #515647 01/11/20 04:35 PM
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Tracy it will be interesting to see how your tube diffusers last.

One claim to fame of membrane disk diffusers is self cleaning. But I still have to clean mine. smirk

Last edited by snrub; 01/11/20 04:35 PM.

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Re: Diffuser heads
TucknDucks #515653 01/11/20 09:31 PM
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Here is my commentary about those diffused aeration systems. In theory the diffuser is great. In long term practical application it may not be so great. Here is my main problem of several.

The tubes produce many 'nice' fine bubbles, however the tube surface has a rough and quite porous texture. See the close-up picture on the website. Initially tested the best, but how long is the efficiency maintained??

This extensive rough interstitial surface area compared to smooth rubber or vinyl is a prime place to grow benthic slime, bacteria, and all sorts of attached algae plus collect sediment in all the nooks and carnies of the rough surface. It is amazing what microscopic 'stuff' tightly adheres to all those nooks and crannies. As the stuff increases in density it becomes more visible, dense and thicker. All these things clog deep into the pores toward the outside of the diffuser and reduce its overall efficiency. Then - how does one clean the rough textured porous surface on this type of diffuser?? Cleaning deep into the pores is very difficult, if even possible. Diffuser clogging reduces the water movement of all diffusers and causes increased back pressure to the compressor thus shortening comprssor life span. Compressors are not cheap!

A past aeration expert and associate of mine here Ted Lea (Forever Green) gave me one of this type of diffuser to test. He was disappointed with its relatively short term performance. Years prior to that, I had "been there done that" with the same diffuser plan using that style of rough surfaced texture diffuser material. Great bubble production but high clogging tendency. The diffuser sits in my garage.

Another item is the Kasko tests were conducted using brand new systems working at peak efficiency. How quickly does clogging occur and what are the variable test results when the diffuser gradually and continuously becomes more and more clogged? How efficiently can a diffuser surface be cleaned - a very important factor when choosing a diffuser.

Last edited by Bill Cody; 01/11/20 09:52 PM.

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Re: Diffuser heads
Bill Cody #515664 01/12/20 01:57 PM
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I echo Bills comments. I've seen more "difficulties" with the tube diffusers than with the flat disk type diffusers. As for cleaning them, even the Vertex diffuser disks get growth on them and for optimal efficiency they should be cleaned once a year to keep the bubbles from coalescing. I don't worry about cleaning the diffusers that are for winter use because I want coarser bubbles to create movement on the surface of the pond.

Air stones are the worst for cleaning, about the only way I know is an acid dip to clean them.


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Re: Diffuser heads
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Cleaning the ceramic air stones instead of an acid dip actually requires a soaking in the acid (muratic) because the growth and minerals become deposited down into the pores of the diffuser stone.


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Re: Diffuser heads
Bill Cody #515668 01/12/20 05:50 PM
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Originally Posted By: Bill Cody
Cleaning the ceramic air stones instead of an acid dip actually requires a soaking in the acid (muratic) because the growth and minerals become deposited down into the pores of the diffuser stone.


Bill, that's what I do with the air stones in the holding tanks that use air. My diffusers that are used with straight O2 don't get dirty - they aren't in the water unless they have O2 going thru them.


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Re: Diffuser heads
TucknDucks #515673 01/13/20 06:08 AM
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I laugh at myself when trying to discuss pond tec stuff with Bill Cody and esshup. You both know I don't know much about pond stuff lol. For now I just thought I would throw out my experience for anyone interested. As far as cleaning the tubes, When water warms up, I will pull them up and take a medium stiff bristle brush to them. I only clean what I can see and have no idea on how many pores might be clogged. I don't spend a lot of time cleaning them with the brush. but just enough to clean off anything I see that's hanging on to the tube area. After that I isolate the air from a few of them to increase air amount to each for a good blowing out. I will say for now (based on water temps) it will turn the pond over as needed for now.

I know from the past five yrs of reading here that Ted Lea made a good impression with people and was very knowledgeable when it came to all this stuff. I'm sure he is missed.


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Re: Diffuser heads
Bill Cody #515675 01/13/20 07:36 AM
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Nice thing about it is, whatever type of diffuser a person is using, as long as they have a way of extracting it easily it is not a huge expense to change diffusers or even the type of diffuser.

Once the big expense of the pump and hose is in place, a person can play with different types of diffusers or change them out as needed.

At least a person is not starting out all over again with a complete new system.

I think my diffuser disks have been in about 4 years now. I could pull the bases screw in 8 new disks for probably under a couple hundred bucks.

Might not be a bad idea instead of waiting for them to fail.

Another thought I just had, have a spare set. Instead of pulling and cleaning, just switch sets so the dirty set could be cleaned an stored ready for the next "cleaning". Have to think about that.


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Re: Diffuser heads
snrub #515697 01/13/20 08:46 PM
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When cleaning the smooth diffuser disks, I use a white scotch brite pad, like you see in the stores for cleaning dishes. Non-marring like the green or brown and cheap enough that you can toss it when you're done. I leave the disks in the water when cleaning, and have someone on shore turn the system on to check the bubbles coming out after cleaning.


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Re: Diffuser heads
TucknDucks #515838 01/18/20 07:39 AM
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Thanks for the help everyone.


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