Pond Boss Forums AERATION Systems questions Presure volume?

Hey folks, what is the most CFM one should put to one vertex disk?

Cheers Don.

EDIT: is there a pressure reading one should shoot for?

Other 9 inch disks I've worked with (EDI) have an operational range of 0.5-4.0 CFM with a max of 6.0 CFM

The pressure should be related to the depth of the diffuser (pressure to overcome the head pressure of the water column) and not the flow rate.......UNLESS.......... there is an internal restriction built into the diffuser AND flow rates are sufficient for the restriction to cause a pressure rise.

The Matala's I use have no internal restriction but I have heard some others do. The internal restrictor could be to protect from over expanding the membrane by limiting excessive flow rates or as a mechanism to help divide flow between multiple diffusers.

So if you are operating within the design limitations of the diffuser, you should be looking at head pressure of the water or in other words about one half psi for each foot of water depth.

FWIW I would ask Vertex the CFM question. IMO I agree with Snrub with respect to your pressure reading. There is a minimum pressure required to get to the depth of the diffuser which is just at zero flow. Increase the flow to get bubbles and the pressure will rise above that required to get to depth. The pressure rise to get the desired amount of bubbles will be quite small compared to that required to get to the depth.

Keep in mind that Vertex diffusers have special built-in valves for balancing air flow among multiple diffusers, thus they require slightly more psi to make the diffusers work properly compared to most all the standard or commonly available membrane diffusers. Optimum air flow to most single diffusers is 0.5 to 1 cfm, although membrane diffusers are designed to operate at higher air flows of 1 to 4 or even 6 cfm. As the airflow exceeds the optimum cfm the membrane slits open wider and bubbles are bigger then reducing the efficiency of the air flow to the diffuser. Remember - smaller bubbles mover more water compared to the same air flow using larger bubbles. When in doubt check with each manufacturer for specific flow ratings.

See I guess this is a funny one because as the PSI gos up the CFM should and as the PSI gos down so should the CFM.

So my thoughts are that if the PSI needed is at say 10 feet your looking at .44 X 10 feet plus 14.7 for the atmosphere I get 19.9 psi at one CFM is required for one disk to work optimum correct?

Cheers Don.

Donno:

Shouldn't the volume stay the same? Air is compressible. If a diffuser needs say 1 cfm to work at optimum, wouldn't it need that same cfm at all depths? As the diffuser disc goes deeper into the pond, it needs more psi to operate. But, at depth, since air is compressible, wouldn't the cfm stay the same even though pressure increases? Pressure increases at the compressor to overcome the psi needed at depth.

The diffuser would "see" the same opening psi as it would on the surface.

Take a diffuser disc at 20' depth, just to easily round off numbers. .5 psi for every foot of depth needed, correct? So, at 20' depth, you would be seeing 11 psi on the compressor, but the diffuser would still only be seeing 1 psi in the airline vs. the psi on the outside of the diffuser.

Since air is compressible, what would be the volume of air at 11 psi vs. at 1 psi? Would it stay the same? (I don't know)

From a theoretical point I believe it depends on where you measure it. From a practical point, if 1 cfm is supplied at the surface compressor it will again be 1 cfm when the bubbles reach the surface.

But back to the theoretical, as the air is compressed it reduces the area it is contained in. So if there were a flow meter at depth, it would read a lower cfm reading, because the air is more dense.

Eons ago we used to use a balloon for demonstration purposes scuba diving in the swimming pool or lake. The instructor would take the balloon to depth, partially fill it from an attachment hose coming out of the first stage of his regulator, then release the balloon. If filled just right or if at great enough depth, the partially filled balloon would burst before reaching the surface. The object lesson for divers was that if you breathe compressed air at depth, then hold your breath while assending, your lungs would do the same thing. Not a good thing.

So as the air becomes denser with depth, the pressure has to increase to keep it moving deeper and the volume it displaces becomes less, thus a lower flow at that depth measured in cfm. But once the air is released from its pressure it expands back out to original.

So from a practical standpoint, 1 cfm at the surface that the pump puts out is still 1 cfm when the air reaches the surface in the form of bubbles. But at it compresses the volume decreases as the density increases and the velocity slows. That is why it is more important to have a big line near the compressor and a smaller one is ok nearer the diffuser on very long hose runs to deep water.

On my diving regulator the hoses from the first stage (on the tank) to the second stage (at my mouth) is very small. Probably a quarter inch in diameter. If I were to try and breathe atmospheric pressure air (as in using a snorkel) through this quarter inch diameter 2-3' long hose the breathing would be difficult at best. Like breathing through a small diameter straw. Yet at 125 psi the first stage delivers to the second stage, there is plenty of air because the dense air in the hose expands as it drops in pressure to my breathing pressure (atmospheric pressure at the surface, not quite 15 psi at one atmosphere or 33 feet depth, not quite 30 psi at 66 ft depth and so on). It is hard to imagine but when I'm at 135' depth if I were breathing from a hose supplying air from the surface, the air pressure I am breathing and the compressor would need to supply is just under 60 psi. But since the surrounding water column pressure is the same, my lungs see it no different than breathing atmospheric pressure at the surface. But I dare not hold my breath as ascending - because as I go towards the surface my lungs are trying to hold in 60 psi air. Not good.

More than anyone wanted to know.

Way cool read. Thanks for that.

I do remember when my brother was taking scuba diving he was told to not come to the surface any faster then the smallest bubbles are and every ten feet or so decompress his ears.

Cheers Don.

A well supported brand of air pump will have a PSI to CFM chart (see attached) so you can estimate the CFM given the current resistance/load (PSI) your air pump is currently under. It is important to remember that PSI is inversely related to CFM. The more PSI the less CFM because your air pump is working harder.

Fascinating! I recently became SCUBA "certified", and we went over all of these pressure-factors in class - but your concept-explanations achieved what took my instructor a half day to convey. Great job!

Congrats on your new certification! I bet you will find observing fish in their own element very interesting.