Compressing air under water?
by Steven DeAngeles
If I had a air compressor under water (in a sealed container), approximately 150 feet, with a tube extending above the water surface for air intake would the compressor require less energy since the air would be compressed by being 150 down? Bill answers... Hello Steven... Boy, I get some interesting questions on this site, and some, like yours, really tax the old gray matter. Not being a SCUBA diver, I have no idea how many atmospheres of pressure the water would exert at that depth. Let's guess that it's 20 atmospheres at that depth, just for sake of example. In order for free air to reach your compressor then, the snorkel tube would have to be able to withstand the water pressure exerting about 300 pounds of force on every square inch of the tube itself (20 x 14.7 PSI) as it neared the compressor. Assuming it did, then you would have free air at 14.7 PSI (one atmosphere) entering your intake port of the compressor as the snorkel tube would prevent the water pressure from exerting itself on the air inside the tube. If the compressor is in a sealed container, and you have a way to keep the water out, then wouldn't the ambient air pressure in the compressor area be at 14.7 PSI? If the tube supplying the air and the capsule in which you have the compressor are strong enough that they don't react to the water pressure outside of them (crush under pressure), then the air inside the tube and compressor capsule would not have reacted to the water pressure. That being the case, that the supply air is at 14.7 PSI and the compressor is in an environment of 14.7 PSI, then I would surmise that there would be no mechanical or electrical advantage to the compressor's operation and the air compressor would require no less energy than if it were operating on the surface. Not being an engineer, these are just my thoughts on the matter. Other opinions are certainly welcome and may even be more accurate! :-) Cheers, Bill
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