hydralic question,?

[BHD]

the question is years ago, they had auto lifts that used air and oil to lift the car,

the air went into a tank that was filled with oil and the air pressure displaced the oil pushing the cylinder up lifting the car,

here is the question, did the surface of the oil act like a piston, thus mupliting the pressure on the oil, or was the oil the same as the air pressure?

in one way say a 6 inch tank, = 28.6 square inches, and say you put 50 pounds of air in the tank, what is the pressure of the oil exiting the tank at the bottom, (say via a 1/2 port)?

one way I would say it is 50 psi and another way it looks like it could be, 1413 psi.

what is the correct answer?

 

[BukitCase]

Your first way is correct - inside a vessel the pressure will equalize, whether liquid or gas. Where you get multiplication is when that pressure is applied to a piston. Then the surface area of the piston multiplied by the PSI, whether air or liquid, gives you the generated force.

- this is why those old lifts had a ram (piston) that was at least a foot in diameter - if you take a 12" piston and use air pressure to force oil out the bottom of a tank and up into the cylinder (because oil is heavier than air), you have a surface area of 6x6xpi, or slightly over 113 square inches - apply 150 psi to that area, and you get 16,964 pounds of force.

Not sure, but I'm thinking it was done that way because every service station had an air compressor, but not necessarily a hydraulic pump (or the need for one)... Steve