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#463076 02/01/17 05:37 PM
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I would like to use a standard oil less compressor to charge LP tanks for aeration of my pond. I have a 2/3 acre with 22 degree banks to 15 ft. deep. How much air do I need to turn this over? I would like to use two membrane diffusers. Which would be a better choice the flat style or round, and how large should they be. How far apart? I was using a GAST pump which ran 24/7 and it don't like the stone diffuser getting clogged. I am trying to get better efficiency by charging the tanks and regulating flow with valves. I am totally ignorant on this subject and am not sure if it even makes sense. Lot of calculating to do here to make this determination. Any insight would be greatly appreciated.

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If the diffuser is clogged the air pressure gauge will register more than 1/2 the depth of the deepest diffuser. If the unit does not have a low persure air gauge the above problem is one more good reason to get one installed.


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As I said, I am ignorant. I have installed the gage to figure out the problem. Now I am looking to build a system. It seems to be to complicated, I have had no luck getting anyone to respond on any forum. I guess I will just have to go to the professionals at the NRCS office. I was hoping to get recommendations and buy my requirements where the recommendations came from.

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Here is a current thread that has some information.

75 year old pond

If it is just the equipment you want a google search will bring up lots and lots of places selling aeration equipment. Pumps, air line, diffusers and complete systems. If you want advice specific to your application look around the Pond Boss web site at some of their advertisers. There are experts available who will design and sell you a system that works right from the get go. If you want to experiment do a google search for aeration with the words pond boss forum in the search. A bunch of old threads with information will come up.

If you are looking for a single paragraph solution to what is a complex problem........ well good luck with that.

Welcome to the forum.

Last edited by snrub; 02/02/17 09:41 AM.

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Also good luck with good knowledgeable aeration detailed answers from the NRCS. The most you can expect them to know is aeration is beneficial for ponds.

Your are correct, air stones are prone to clogging, but so are ALL diffusers to some degree, clogging rate depends on each pond conditions and style of diffuser. Some diffusers are much easier to clean than others.

IMO your first basic error is to use the GAST compressor to charge two LP tanks. Not necessary for various reasons. Two styles of standard compressors from Gast & Thomas for aeration are the rotary vane and rocking piston (aka wobble piston). See piston style pump info below. The rotary & rocking compressors are designed and are apply used for aeration because they are built to run continuously. Although if you can circulate your pond in less than 24hrs, then 24/7 operation is "normally" not necessary - this depends on many chemical, biological and pond morphology factors. Most aeration suppliers say, operate 24/7 to best cover all aspects or variables - plus IMO it results in more pump maintenance a benefit to the company.

For these two style of rotary/rocking pumps you want to use all the CFM of air they produce; send it all to the diffusers, make as many water lifting bubbles as possible - do not store it. The philosophy of storing air in tanks is for piston and/or some diaphragm compressors that are built to pump-up and rest between cycling episodes. Continuous duty compressors are built to 'handle' continuous operation, but it is not a requirement.

Depending on the output CFM of your compressor you might be more efficient in air use if you increase the number of diffusers. Each diffuser is capable of moving a general amount of water gallons/minute or hour. Gang the diffusers together to a point and you move more water per hour and turn your pond over faster. "Generally" for average ponds one compete turnover per day is adequate. But what is an "average" pond. If you don't circulate it enough a fish kill becomes more likely. This is why aeration places say run 24/7. Less operation than that becomes more risky for fish kills especially when the pond owner does not know the pond's BOD (biochemical oxygen demand) or they do not have an oxygen meter to monitor DO at the bottom.

Snrub is correct ""If you are looking for a single paragraph solution to what is a complex problem........ well good luck with that."" Pond aeration is a steep complicated learning curve and few if any are anywhere near the top of the curve.

Last edited by Bill Cody; 02/02/17 11:25 AM.

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I am not using the Gast pump thru the LP cylinders. I was using it with a stone diffuser which became clogged and over heated my pump. I would like to minimize this occurrence and possibly be more efficient by using more diffusers, and by using an oil less compressor to charge pressure vessels of a size large enough to allow for a once a day running of the compressor.

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I think what folks are wondering about is the complication of pressure vessels and trying to predict ahead of time how that would work. If the concern is that the compressor should not run very much or will 'wear out' I think most of us have found that using the proper compressor designed for the task will give you years of hassle free and maintenance free service.

The compressor I have, designed by Vertex and professionally sized for my specific need (by a very helpful PB member) has an expected life in 'years' when run 24x7 as long as I take reasonable steps to protect it from the elements and keep the air filter clean. I run mine usually only 12 hours out of any aeration day and only during certain seasons of the year.

I think if you get a compressor designed for the task you will be happy with how simple your set up will be. Get the good diffuser disks, weighted tubing, proper size compressor and you will be good. Of course anyone can have diffusers get gummed up (they claim 'self-cleaning' but still need a periodic soft glove or soft brush treatment) and they can need cleaning and I imagine an air line can freeze up but most people do not report headaches with this.

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osvrat - What do you mean by overheating the compressor??? How did you determine it was overheating????. If it was truly overheating engineers at Gast told me their GAST rotary units have a auto-thermal shutdown set at a temperature of around 256F. These compressors standardly run at 205F. Remember - water boils at 212F. Thus the rotary compressors are designed to operate normally at a "hot" temperature. If your compressor is just operating 'hot' and not thermally automatically shutting down, then your assumption of overheating is incorrect. Since this style of air compressor operates normally at a hot temperature, this is why it is VERY important to provide good ventilation and air circulation where the pump runs to minimize issues of overheating especially during the mid-summer hot days when it is in a small cabinet.

Last edited by Bill Cody; 02/02/17 02:16 PM.

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Let me explain better. The system with the Gast pump and stone diffuser worked great. In less than 90 days the diffuser plugged causing the inline pressure to rise to 30psi. overworking the pump and the thermal override kicked the pump off. The melting temp indicator had activated verifying this. I am not blaming the pump or system other than how fast the diffuser plugged. I live in Iowa and the pond freezes, so now I have a 30 ft diameter hole in the ice and cannot get a boat out to clean or replace the diffuser. I do not want this situation to happen again, I have to wait now to get my system running again. If I change to a compressed air system with diffusers I can control how much air is let out by volume. Not a set flow like with the Gast pump. When the diffusers plug I will be able to slow the amount of air to not over pressurize the system. My efficiency of moving water will suffer until I can get to them but it will still work in a diminished capacity. I can monitor this with a low pressure gage. I am hoping to build a system that I can control better. With a fixed flow system I do not have this option.

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Originally Posted By: OSVRAT
......the Gast pump and stone diffuser worked great. In less than 90 days the diffuser plugged causing the inline pressure to rise to 30psi. overworking the pump and the thermal override kicked the pump off. ....


FWIW my first attempt at fixing the problem would be getting rid of the air stones, switch to membrane diffusers and leave everything else in your original system alone. I base this recommendation on the fact that the vast majority of the folks that post here on the forum that aerate have membrane diffusers and do not report your short 90 days to clog problem. Hey, if it doesn't work you can always pursue your LP tank idea. Since you were already planning to buy membrane diffusers, it won't cost you anything to try the proven method first before going to the LP tanks.

Just my 1 cent....

Have you calculated how big the LP tanks will need to be to supply the required quantity of air and how long it will take to fill them?

Last edited by Bill D.; 02/02/17 07:24 PM.

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I have heard others using those type pumps recomend an over pressure relief valve to protect the pump. The places that sell the pumps usually offer them.

I would get rid of the stone and go to a 9" disk membrane diffuser.

The way to control pressure is install a "y" with a valve and bleed off any extra air you do not need at the time.

I have thought of using air tanks, but not for the purpose you state. If a person had a fairly large tank you could run the air through the tank first. This would allow the air to cool and condensation drop out into the tank (drain valve on bottom to get rid of moisture) before entering the lines to the diffusers. This MIGHT help prevent winter air line freeze up. I've not done this so it is just a theory.

Last edited by snrub; 02/02/17 07:47 PM.

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I am a not an expert here but this seems like an overly complex solution. Why not use the membrane diffusers like suggested and just clean 2-3x per year. IMO, would probably be problem solved. I have membrane diffusers running in an extremely remote environment. I just make sure to clean them really well as late as I can in the fall. Then clean again in the spring. It's a very simple process.


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Osvrat I am not that familiar with the stones but believe the disk type membrane diffusers will handle a lot wider range of flow rates and still be within operating parameters. Thus if you choose the right diffuser there likely would be no need to bleed off air, unless for some reason you just want to turn less water volume some times.

I think a single diffuser disk is around 30 bucks or there abouts. More if you want a factory base to go with it. You can see both the factory bases and a concrete one I made in the links I gave you above.

Last edited by snrub; 02/03/17 09:02 AM.

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osvrat - okay more information helps, just like going to the doctor. Adding to my post above, your second biggest error was not having an adjustable pressure relief valve on your compressor manifold. An adjustable relief valve allows you to determine the pop off pressure based on the needs of your unique situation.

Certain pond conditions and water quality causes diffusers to clog at different rates. Evidently your pond has a high clogging tendency for diffusers. Choose the diffuser with a los clogging rate (usually rubber or vinyl membrane) and BUY an adjustable pressure relief valve and use it. I normally set the valve for full pop off at 15psi for rotary vane pumps. This small item protects the most expensive part of the aeration system - the compressor.

Last edited by Bill Cody; 02/03/17 07:44 PM.

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Thanks for the advise on the over pressure pop off I like that. I still have my initial question, how much air do I need to turn over this little pond. The system I am trying to design is multi purpose and will allow for a lot of operator control might be complicated in theory but has some tangible benefits. I spoke with a fella who rebuilds the Gast pumps and he said two years is the average life span, and two hundred dollars gets you back on the road. I am hoping to do better than that. Thank you for your advise I will get some better diffusers and use my existing pump. When it all fails again I will have the information to experiment with my design.

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To tell you how much air you need to turnover this pond you are not providing enough basic info for me to do the estimates. Needed: A. air flow of pump in cfm which has some to do with the hp.
we will assume diffusers are at 15ft deep (~7.5psi). You say you want to use two membrane diffusers. How big (dia) are they? Are they disk, tube, or homemade? What are the pore sizes of the holes / slits? Some brands are better than others. They are all factors.

I can tell you that for 4cfm, 4 diffusers ganged together with 1cfm going to each or all 3.5-4cfm to the 'gang' will turn over the 0.66 ac pond two times faster than 2 diffusers. Some diffusers will operate well with 0.5 cfm which means if your pump produces 4cfm at 15ft deep you could operate 6-8 diffusers, not just two. Putting too much air volume into a diffuser expands the slits / holes larger and this lowers the efficiency of the diffuser.

If you are really interested in efficiency use 4 diffusers instead of 2. A gang of 5 vertex 9" dia disk diffusers using 4 cfm will turnover your pond once every 2 hrs. Thus 4 hrs of pump run time a day should be all the aeration your pond should need daily Apr-Nov. Your GAST compressor if in new condition and well maintained should then last a minimum of 15-18yrs on the first set of carbon vanes. However you 'smoked' your compressor once by not having a pressure relief valve, so my estimates don't mean much.

I also rebuild GAST pumps. If the pump is maintained properly and the diffuser is sized properly for the pond size and volume where it does not have to run 24/7 your GAST pump should last 20 years not 2! My rotary is 18 yrs old on the 1st set of vanes. The vanes have a typical life span of 10000 hrs at 10 psi; comparatively longer if pump runs less than 10psi. Motor bearing standard life is 30000 hrs and longer when not running at 10psi. Normally you should go through 3 sets of vanes before the bearings go bad assuming GOOD maintenance. Believe who you want.

Last edited by Bill Cody; 02/04/17 02:41 PM.

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I have 2 Vertex XL/2 diffusers approx. 175 ft apart in my rectangular 7/8 acre pond at a depth of 8-10 ft. Air supplied by Gast 0523 pump. Once a month I close the ball valve on one XL/2 diffuser, sending all air through the other, then reverse the process. My thinking is the extra air flushes pores that may have become blocked during normal use. I seem to have a better boil afterwards. I haven't felt the need to do more yet.

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Pulsing air to the diffusers does help "clean" the pores especially if the diffusers are each receiving low volumes of air that cause only slight opening of the slits. However make no mistake, lifting and scrubbing the diffusers results in a much better cleaning and better later operation with a longer time of good bubbling of the diffuser compared to an air pulsing of the diffuser.

Last edited by Bill Cody; 02/04/17 02:43 PM.

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Thank you all who chimed in. That is exactly what I needed. I had the GAST pump checked and it is still good to go, so I will use your advise to the letter and hope for the best. I will use the multiple diffuser set up. My concern for non 24/7 operation is winter freeze when the water comes back into the line during non operation times. How do I insure against that? Just an fyi it took an act of God and the engineers at Iowa State to get me a formula on the capacity of compressed air in a fixed size container. A 100 gallon tank at 70 degrees with 120 psi will hold almost 68,000 cubic feet of free air.

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Curious - what pump are you planning to use to fill the LP tanks with compressed air?

Winter freeze - Okay. Most, but not all membrane diffusers, have built-in check valves. When your membrane check valves are working properly and not coated with bacterial slime they will keep water out of the airline. This is where a low pressure gauge becomes very IMPORTANT. When the pump starts the air gauge should climb to operating pressure or 1 psi higher and then quickly drop back to normal run psi. IF the gauge climbs to 3+psi for any period of time or the pressure relief valve pops-off before dropping back to regular run PSI, this means the system is pumping water out of the airline; check valves are leaking and need 'attention". If you run the aerator 24/7 then there is less chance of a frozen water plug in the airline. HOWEVER - this can happen. Humid air heated by the compressor will cool and condense water into the airline. This water can collect in low spots of the airline until it is deep enough to freeze an airline plug.

If there is a frozen airline water plug you can pour about 1 cup of isopropyl (rubbing) alcohol into the airline. Wait 20-30 minutes and try running the pump while watching the air gauge.

HOWEVER - in ponds that get ice cover, it is wise to clean and dry out the diffusers every fall so they are at optimum going into winter. The other option is to install a second check valve between the airline and diffuser base.

Last edited by Bill Cody; 02/05/17 02:50 PM.

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California Air Tools has a pretty good line up of Oil Less compressors. Their 2 hp models are adequate, but I am looking into the 4 hp unit and running 220v. A large unit like this will require a lot less cycle time to recharge the pressure vessels. It is without a doubt overkill for the aeration of a pond, but I use a lot of air tools that require significant reserve capacity. If a fellas got to run a compressor I think that multi tasking may have some merit. The use of low pressure gages, and pressure relief valves along with a high quality metering valve I am hoping to accomplish my goals. Your advise has put this on hold and I am excited to see if I can make this all work for me. I have already purchased a pump that still functions per spec, and I am going to buy 2 9" diffusers anyway, so with a few gages and valves which I will need anyway I got nothing to lose and one less project. Thanks for all of the advise.

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With increasing energy costs, a larger compressor might be very costly to operate, considering the number of cfm you need per day.

Here is why Bill is saying that aeration is complicated. You need to turn over the water in the pond "X" per day. Personally, I like to use 1 to 1.5 times per day as a target rate. You need to calculate the number of gallons of water in your pond. Then if using Vertex membrane diffusers consult this chart:


Each diffuser disc needs approximately 1 cfm of air at 1/2 the psi of the depth that the diffuser is placed at. i.e. 12' deep, 6 psi.

If it was my pond, I'd go with a 1/3 to 1/4 hp compressor and a couple of diffuser stations, 1-2 in the deepest part during the summer and one set at 1/4 total pond depth near shore during the winter.


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