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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?

    http://img235.imageshack.us/img235/4540/piston1lh2.th.jpg [Broken]

    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.
    Last edited by a moderator: May 2, 2017
  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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    Gold Member

    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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