As I understand air movement, pressure, and water depth, I think rewording some of what RC51 has mentioned above is necessary. No offense RC, just trying here to clear some 'muddy water'. Someone expert please correct me if I am wrong in my message.
RC51 says: ""I have a pump that will produce a max CFM of 7. And a max air pressure of 5.1. Well if I remember right you will lose about 1psi for about every 2.5 feet or so of water downforce and my system is in 8 feet. So at 8 feet my system is producing about 2 to 2.2 psi."" I think there is a 'little muddy water' here.
I will reword or re-explain this. As water depth increases it takes more air pressure to exhaust (push out) air at that new increased depth. As a simplistic generalized rule I use 0.5 psi per ft of water depth. Example: to blow air at 5 ft it requires about 2.5 psi, exhaust air at 10 ft then it requires 5 psi, etc. As one goes deeper you really don't 'lose' psi, you usually lose cfm (air volume). But it does require MORE psi to get air out at increasing depth. A specific psi has a depth limit to which it can 'blow air" and expell it. If you don't have enough psi (pressure) you don't or can't 'blow out' any air at a specific depth. Try blowing air out a tube with your mouth when it is 5 ft deep. Just tried it, can't do it, cause my lungs could not create enough pressure (psi) when the tube wass at that depth. 2ft yes, 3ft yes, 4ft difficult, 5 ft no way. You can try this at home.
Now, as you blow out a measured rate/amount or volume (cubic ft/minute - cfm) of air (not same as pressure), AND you increase the depth, the amount you can blow out becomes less unless you increase the pressure - psi. This becomes critical when the compressor has an upper normal working pressure - say 10 psi (most rotary vane pumps). Generally as one increases depth, the amount or volume rate, (cfm) that is released becomes less due to increased pressure from water depth. Standard air flow rates are available for each type of compressor.
At 8ft deep, RC51's pump is not producing 2 to 2.2 psi as he states. A low pressure air gauge will verify this. If RC's pump was only producing only 2.2 psi, it would not be blowing air out at 8 ft deep but only to a max of 4-4.5ft deep; deeper than that no air is released, unless one increases the air pressure (psi). At 8 ft deep, psi or air pressure has to be 4 psi or no air will come out the hose. An air pressure gauge verifies this fact.
I think RC has psi and cfm confused. Since RC's pump produces 5.1 psi and 7cfm rating (I assume open flow no back pressure/resistance), then at 8 ft deep he probably only gets 2-2.2 cfm of air out his hose at 8 ft deep, because of the max pump pressure of only 5.1 psi that his pump can produce. If his pump had more psi, it would be able to gererate more air flow (volume,cfm) than 2-2.2 cfm at 8 ft deep.
Is all this clear as muddy water? Is so just add some alum, gypsum or lime, and give it time for things to settle, then it might clear up?
Last edited by Bill Cody; 03/26/11 11:28 AM.
