Pond Boss Forums AERATION Systems questions Compressor/Diffuser Pressure Question

Last September I installed two 9" disc EPDM diffusers in my little BG pond (~300,000 gal). The diffusers are rated for 0.5-5 scfm. Each diffuser has its own airline (about 50' in length), one being 1/2" tubing (11' depth), the other is standard garden hose (8' depth). The compressor I started out with was rated for 1.5 cfm @ 10 psi. The compressor would only handle one diffuser at a time. During operation, the pressure gauge was registering 4-5 psi.

Recently, I found a compressor rated for 2.6 cfm @10 psi and decided to give it a try. This compressor produces enough cfm so that I can run both diffusers simultaneously and produces a nice rolling boil on each. During initial startup which was about 2-3 weeks ago, the pressure gauge was reading 5 psi. Today I happened to look at the gauge and noticed it is now reading about 8 psi.

Excluding the pressure gauge, any ideas what could have caused the rise in pressure?

I would think is reason is the temperatures are changing on the compressor,airline and outside temperature.As these change i would think it would rise 10-20% from your starting point.

As the diffusers get dirty and start to clog, the back pressure should be higher. I've no idea if it could make that big a difference this fast.

Theo and Steve have good points. Both will register a little bit difference in pressure. More so with Theo's Hypothosis.

I would dare to say with a 3 psi change, you may have dropped your diffuser down to a deeper depth. If you are achieving a larger and "nice rolling boil" this would increase the amount of bottom debris that is being entrained into the water column. Your 9" diffusers have dug themselves a hole and the increased pressure is the result.

I would agree that there has got to be something that has changed but I can't imagine that it's clogging that quickly. I have a 9 inch diaphram diffuser in my pond and the pressure required to get air through it hasn't changed measureably in 4 years. I do not run my air 24/7 however and that could tend to keep mine clean by excercising the diagram every time it goes on and off. I also don't think it could have dug itself deep enough to add 3 psi, it would have to dig itself over 6 feet deeper. I'd check to see if perhaps an air line got kinked or something like that. My diffuser came with instructions on how to blow it out. You give it a blast of air at a higher PSI that will stretch the diaphram and open the pores so they clean out. You might try this to see if it causes the pressure to drop back down. Don't us too high a pressure or you'll blow the diaphram right out of the unit. Check with the manufacture for maximum psi rating.

Thank you for the replies.

Theo, the diffusers were new last fall. I did not run them through the winter but when I started aeration in April,with the old compressor, the pressure gauge read about 5 psi.

Cary, this pond was expanded in size and depth last August so there was no bottom muck when the diffusers were installed. I've only had the new compressor(2.6cfm) hooked up for 2-3 weeks. The unit is set to run for 2 3hr times periods at night. Do you think in this short amount of time the diffusers could be excavating a hole enough to result in a psi increase?

Bz, Before installing the diffusers, I put them in a tank and blew air through them using my shop compressor. You are right, you can blow them right out of the housing if you are not careful.

Steve, like a good portion of the US, temps have risen about 15-20 degrees since the new compressor was hooked up. I wonder if anyone else has noticed an increase in psi.

One thing I would like to do is find a nice liquid filled gauge that only goes to 15 psi. The one I'm using now is not liquid filled, the needle flutters a bit and psi increments are open to argument(what I'm guessing is 8 psi, may only be 6 or 7 to someone else.)

Russ I sent you a private email.

Heating of the air in the gauge should make the psi be less not more. If you truly are operating at more psi then something is causing greater back pressure. Possibly an air restriction maybe a kinked airline? Remove the diffuser from pond, uncouple it from hose and run compressor, gauge should read zero if there is no air restriction in airline. IN many "normal" cases with the clean pore diffuser out of the water while operating the compressor the gauge should read zero. Clogged diffuser pores will cause some backpressure with diffuser out of water. Real long airlines or small diameter airlines will cause slight backpressure with diffuser out of water.

Russ, if you have a cheap gauge I would definitely replace that first. I had this same problem when I thought my pressures were climbing one time. Turned out to be a worn out, sticking gauge. I'd replace the gauge with a new good one. Of course this won't tell you squat about whether you had a pressure increase occur since you don't know if the old gauge was reading correctly. But if the new gauge reads something you can live with just sit tight and see if it changes over time. In the mean time do all the checks Bill mentions just to make sure you don't have something restricted. I didn't comment on this before but Bill is right that warmer air will not cause higher pressure when you are pumping it through a hose and diffuser. Warm air does increase pressure in an enclosed container but that's because it is enclosed and the air is expanding. In your aeration system warm air will also expand but will travel out of the system under the same pressure it would normally take to pump air through the pipes and out the diffuser. The pressure required to push xx gpm through your system is mostly a function of how much restistence there is to flow. It is true that a small un-measurable drop in pressure might occur since escaping air is slightly less dense and thus may slip through the diffuser a little easier. But this is very negligeable when talking the small temp changes you are experiencing from the weather.

After installing a new gauge (thanks again Bill)the pressure reading is back to 5-5.5 psi.

The "new" compressor seems to be working fine with a good boil from both diffusers. I've cut the runtime from 6 hours with the old compressor to 4 hours with the new compressor. Maybe I'll even say a few bucks.

Thanks to everyone that replied.