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How do I seal an axle and a piston from water intrusion?

I have a motor with a 1/4 metal axle on it that turns a propeller in water. There is a pvc pipe around the motor. I want to seal the axle so water can‘t get to the motor. What is the best way to do this so the axle can still turn?Secondly, I am trying to make a kind of piston, with water on one side of the piston, and air on the other. How do I seal the piston from water coming in the inside so that the piston can still move?Also, I hope these seals can handle at least around 50 psi.Thanks a lot,Eric


For the piston, a groove cut in the piston and a rubber O ring will work. It can handle 2,000+psi in hydraulics. The shaft needs a rubber lip type seal. The more water pressure there is, the tighter it squeezes the seal lip onto the shaft preventing leaks.
May 28, 2018
For the axle I would recommend soldering a short hub on the water side of the axle and using a spring, loaded against the hub and to a flat washer against a Teflon or nylon bushing that seals the axle to the hole that the axle passes through. This is essentially a cheap mechanical seal where the flat washer will turn against the Teflon bushing. This type of seal often has a tapered soft bushing so that the water pressure will wedge the bushing against the axle making that seal as tight as you can stand. For the second the size and complexity of the system is not really clear so I would suggest that if the displacement of the piston is not extreme, you could use a flexible diaphragm as a seal. This is the cheapest and easiest way to do this. Piston rings will work but water is not friendly with piston rings unless they are designed carefully. Look at the design of oil-less pumps and compressors for how this works. Scuba diving use oil-less compressors so that the air the divers breath isn't contaminated by the oil.
May 28, 2018

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