Windmill Head Pressure?

Question

We have purchased an American Eagle 28FT. windmill and installed it to spec The wind mill seems to work perfectly. from the blades down to the base of the pond. The wind blows, the blades turn, and air is pumped out of the 1/2inch hose at the edge of the pond.  The problem is when we hook up the two hundred ft hoses with two stones,at a depth of 12ft. the wind mill will not turn ? We have a small refrigerator compressor hook up that puts out enough air to operate the stones. This seems to work at  between 4and 5 psi.

My question is , the head pressure a problem with stopping the windmill from turning ?  
Thanks! FD
 

Answer 1

Hello,

 

Yes it could be the issue. Any compressor, electric or wind powered, puts out a certain amount of airflow at a certain pressure. The CFM output of a windmill compressor will typically increase as wind velocity increases. The more CFM you are pumping into an airline the more friction is built up within the pipe and pressure loss can result. This can cause a back pressure as the compressor cannot overcome the resistance of the air that is literally plugging up the airline.

If you are running say 5 CFM through 100 feet of airline at an initial pressure of 6 PSI the pressure loss in the line will be 6.31 PSI so basically the compressor will be unable to get the air through the line to the diffuser. If your diffuser is in 12 feet of water you need 5.2 PSI to get air to that depth and that doesn't include the pressure loss in the airlines.

 

So if you are running 200' of airline to a diffuser at 12 feet deep you'd want a system that can provide at least 12 PSI to get the air to the diffuser. If the CFM of your compressor is less it will take less pressure to reach the diffusers so it is possible that your refrigerator compressor has a lower CFM output thus the air will reach the diffusers.

I am not sure what the pressure capacity of the American Eagle bellows compressor system is, they seem to mention the high CFM output but not the pressure rating, although they say it can pump down to 14 or 16 feet which would mean their bellows pump can provide about 7 PSI output. Trying to push 4 CFM with 7 PSI through 200' of airline and then down to a 12 foot depth seems quite a demand that may not be possible. If there was only 1 or 2 CFM with 7 PSI behind it you might have results.

A diaphragm compressor can put out 30 PSI which would be recommended for long tubing runs or deep diffuser placement. The OWS Bal-Cam system has 30 PSI output and while it may not have the same high CFM output as American Eagle it has a higher pressure. You will be better off having 30 PSI to push 3 CFM instead of only 6 PSI to push 6 CFM. The pressure drop from a high CFM/low pressure combination could render operation at the poor end of the scale.

More on Pressure Drop in Airlines: http://www.engineeringtoolbox.com/pressure-drop-compressed-air-pipes-d_852.html
Diaphragm Windmill with 30 PSI compressor: http://www.thepondreport.com/store/aeration-system/windmill-pond-aerator

Discussing with your local American Eagle dealer would probably be the first step in getting your windmill operating as it should.