Simple Hydraulics & Pressure trouble

AI Thread Summary
The discussion focuses on the challenges of calculating the pressure required to lift a piston in a tube where the piston diameter is smaller than the tube's diameter. The lack of a seal around the piston complicates the calculations, as it introduces factors like air pressure and potential blow-by. The conversation highlights the importance of piston rings in sealing gaps to improve efficiency, even noting that some high-performance engines still experience significant blow-by despite tight ring gaps. The issue reflects broader concerns in hydraulic systems and engine performance related to pressure management. Understanding these dynamics is crucial for optimizing hydraulic applications and engine efficiency.
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Im having a spot of trouble with some pretty elementary problem.

A mass sits inside a tube which is pointed vertically, the mass is the same shape as the pipe ( i.e. it behaves like a piston ), but the piston diameter is less than that of the pipe.

In order to lift the piston, what pressure must be applied to the fluid?

http://img235.imageshack.us/img235/4540/piston1lh2.th.jpg

The top of the chamber is eventually open to the atmosphere, and is filled with air at STP.

My problem seems to be the lack of a seal about the piston, i can see that it would be simple to calculate if it was simplified to a sealed piston, but with a piston that's smaller than the bore of the chamber its harder.
 
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And that, essentially, is why engines have piston rings to seal that gap.
 
Yep, and even with piston rings you still get blow back.
 
Yeah. How irritating. That 650 hp 440 in my Roadrunner has a .008 ring gap (race-only TRW pistons), and it still wastes tons of potential through that.
 

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