Just a note on 9" round Matala membrane diffusers.

I have three, double 9" stations. This year I had two of the stations have one of the diffusers stick shut. Air was only coming out one side of the dual diffuser. I discovered this while cleaning them. I was diving down with a dive mask and fins, breath holding, and rubbing the diffusers with a golved hand to clean them. Did not make sense why the diffusers were collapsed and no air coming out one of the two disks.

Rather than pulling them at the time and finding out the problem, it was late summer and I just figured would let them run with the single disk till fall when I would pull them up to see the problem. They were still moving a lot of water with the single disk and the heat of summer was over anyway.

Got around to pulling them up today.

What I found when I unscrewed the disk was that the built in check valve had stuck in the air opening. The way these membrane disks are designed, when air pressure stops the disk center has a slight protrusion that covers the air opening and acts as a check valve so water will not enter the air line. It works. I have never had a problem with this check valve sticking in the past. But upon inspection the center protrusion had been forced down into the air opening enough so the modest air pressure would not re-open the valve. So all the air was directed to the other disk.

In retrospect I think I created the problem. I remember pulling the air lines off at the compressor a couple times and putting it back on to "shock" the membrane and potentially clean some of any build up off. I think in doing so the membrane slammed down hard enough to stick the check valve protrusion into the air opening. After I unscrewed the disk off the housing it only took a tiny bit of pressure of a blunt instrument into the air opening to un-stick the membrane. Almost no pressure. So it was not stuck very bad at all. But with the compressor only running about 4.5 psi it was not enough air pressure to open it. Knowing what I know now I will: 1. not remove air lines from the compressor and let the water pressure slam the membrane shut against this built in check valve and 2. if it does happen again will use an air compressor source with enough volume and a temporary "burst" and the stuck membrane should open easily.

I think with the CFM I am supplying, the dual disks are only marginally better than running the air through a single disk anyway. Same CFM, just divided between the two disks and bubbles supplied over a broader area. Probably more efficient at moving water but only marginally considering no extra air flow. So I am not too worried if one sticks shut again anyway.

Just an FYI should anyone run into this situation with Matala dual diffusers.

John

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