Pond Boss Forums AERATION Systems questions Check valves

This was touched on in another thread and I've been wondering about it for some time myself. There is often a reference made to check valves in membrane type diffusers. I was under the impression that it was more a case of a check valve "action", due to the slits in the membrane going closed when not under pressure.

Is there in fact a mechanical, dedicated type of check valve, or is it simply a type of automatic function of the membrane construction? I can see where having a mechanically actuated valve might be problematic....(cleaning, repairing, etc)

There are actual, mechanical check valves. However I have never checked on them for such low pressure applications. The ones I am familiar with are used in plumbing and are brass. I'm sure there are less expensive plastic ones too. Just don't know the ratings.

They make check valves in every imaginable flavor.

Get one with a low crack pressure. McMaster has some PVC and PolyPro pretty reasonable. Check valves may need cleaning for dirty environments, but usually you can cycle them with flow.

Thanks guys...I'm familiar with check valves, I was just curious whether or not a typical 9" membrane diffuser was equipped with a mechanical, stand alone check valve, or if it relied upon the membrane itself to settle down in the "closed" position after air was shut off.

I took a look at some old diffusers I have here, and I can find no valve. I'm assuming that means this particular brand diffuser utilizes the elasticity in the membrane to prevent water from entering.

Membrane diffusers usually have built in check valves. Rarely are the slits in the membrane adequate to stop water back flow. Checking function or mechanism of he membrane diffuser is caused by water pressure pushing in or down on the built in 'check valve' which stops water back flow. Dirt and detritus can build up inside or underneath the membrane. Membrane slits are usually 0.5-1.0mm and phytoplankton, sticky slime bacteria and detritus are often the sizes of 0.00001 to 0.005mm, thus there are lots of things that can build-up and collect or coalesce under and on the porus membranes and at the site of the check valve which is another reason IMO to periodically clean diffuers. Diatoms are able to grow on glass (periphytometer samplers) and stick tight enough they have to be scraped off with a razor blade. Periphytic algae has no problem sticking to rubber.

Efficiency of operation of the check valve can be verified with the use of a pressure gauge. Watch gauge when compressor starts. Pressure should rise to above normal operating pressure for 1-5 sec then fall back to normal operating pressure. If pressure remains high for longer than a few seconds the pump is pumping water out of the airline due to check valve leaking.

Thanks Bill! Perhaps the intended usage of the diffuser impacts whether or not it contains a check valve?

I decided to do some checking. This is what happens when a diffuser meets a bandsaw......

One old 9" diffuser. I don't remember where I got it, or what brand it is.



The same diffuser after disassembly:



The base, where it threads down into it's air connection. There is simply a hole straight through to the membrane, no valves.



The membrane itself.



I'm curious as to whether or not other brands of diffusers are made the same way. Maybe this is a case where it pays to select components not just on price, but with an eye to features included?

I am almost certain fusers come both ways with and without check valves. So yeah its worth an extra few bucks or the right fuser for the built in CV's. The one you have here may just not have ever had one???

RC

The center of the bladder has no slits and uses the force of the water down pressure on the bladder to act as the check valve along with the rebound memory of the bladder itself.The hole in the center of the disc varies from manufacturer and intended use. Some manufactures will use an orifice size that keeps constant pressure to the underside of the disc so that if the disc isn't perfectly level on the pond bottom it will still have the same flow high side and low side. This is also another reason not to operate a disc above the suggested cfm rating as these bladders can stretch and compromise the check valve effect. Some bladders have I slits some C slits, some have the slits arranged in a delta pattern, some have a proprietary rubber composition that gives better "rebound memory" but to look at them they can all look similar ! Hope this helps.

So Ted, are you saying that there is no mechanical check valve, rather a case of the membrane providing a check valve action? This is what I suspected, and in fact that old diffuser I destroyed was very clean on the inside....proof that it works in my book.

A closeup of the "air" side of the membrane. Just like Ted said, there are no holes/slits in the center. Also notice the distinct "ring" in the center of the material, caused by the membrane settling down over the orifice, pushed against the opening by the water pressure bearing down on it, and effectively sealing it off...preventing water from entering the air supply line.

Did I get that right?

That is correct, I have removed many competitive rubber bladders where someone put an external blue Brady check valve at the in water station base for some reason. I suspect because they saw them on airstones and soaker hose type membranes where the external is needed. The problem is when they aren't needed they are just another restriction. When they are needed they are not maintained as there is an o ring that only lasts 12-24 month (as a rule)I monitor my discs with the system pressure gauge and flex often never going over the max suggested cfm rate, My main pond has one display that has a large system in it with 5 stations, I have changed 3 station discs just to show and have the newest generation but still have 2 originals going from the 2002 installation.

Thanks for your help Ted! Been wondering about this.

Nice I always wondered how that worked. Thanks for that info Ted. U too Spark for the detalied info on what a tore up diffuser looks like!! LOL...

Makes sense Ted!

So it's actually a stopper or back flow prevention device, and not really a check valve that will have spring pressure and a positive seal?, which also makes sense in a pond environment. Mechanical things could be an issue here.