Water is an incompressible medium, air is very compressible. Replace compressible by “elastic” and you get an image of what that means.
Any change in cylinder pressure (negative or positive) in water is immediately transmitted to the penis. Air pumping has a bit a “slower” and “elastic” way of transmitting pressure. At the end of the day, pressure/vacuum remains pressure / vacuum in mmHg, but the way the pressure change is made is quite different.
Another point is that water can be warm, therefore transmitting heat while you pump. This is an advantage in my eyes.
So these two points may explain the difference between air and water pumping and the effectiveness of results for the individual users. Water pumping developed quite a hype when Bathmate started the marketing, but I must say that water pumping should be more effective for the reason of hydraulics working better than oneumatics - strictly speaking in terms if physics. I guess that is the bottomline idea behind the messages especially the Bathmate company marketing tries to tell us.
Unfortunately, most water pumps come without a manometer so it’s hard to compare results because of the missing vacuum measurements. Plus the risks of overpumping is higher when you can’t measure the vacuum.
And the really big disadvatage of Bathmate and similar commercial water pumps is tube size. Tubes have to be individual - after all every penis is different. This (and the high costs) has kept me from buying a Bathmate until now. Maybe the right strategy should be to PE until you have the right dimensions for a commercial water pump and THEN ONLY switch to it.
But I have read about folks using regular air pumps or home-made pumps filled with water - and having an individual cylinder, of course. Sounds like a solution to me.
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