Think about it....
Water is so much easier to make HP because it can't compress.
Is not flammable, and can leak on the ground. Only disadvantage is you need a ram thats SS or brass.
The same thing can be done with hydraulics, (but dont use it for oxygen, unless it has 2 different rams.)
My main HP compressor at home.
Is a 6inch diameter hydraulic cylinder with a floating piston. 1cuft displacement, (at 150 psi shop air pumps approximately 10 cuft per stroke,)
Shop air is dryed, and pushes the piston, down. Hydraulic pump runs on a timer and cycles, that's how I pump 95% of all my air,
then I have my portable buaur compressor.