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Simple Hydraulics & Pressure trouble

  1. Aug 13, 2006 #1
    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?


    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 thats smaller than the bore of the chamber its harder.
  2. jcsd
  3. Aug 13, 2006 #2


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    And that, essentially, is why engines have piston rings to seal that gap.
  4. Aug 13, 2006 #3
    Yep, and even with piston rings you still get blow back.
  5. Aug 13, 2006 #4


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    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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