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Estimating shear loss from a piston ring

  1. Dec 30, 2009 #1
    Hi could someone tell me if it is possible to calculate the shear loss from a metal piston ring against the cylinder in a hydraulic pump when the outlet pressure and speed (in rpm) of shaft are known.



    maybe along the lines of in cylinder pressure x piston speed x friction coefficient

    Any help would be much appreciated.)
    Last edited: Dec 30, 2009
  2. jcsd
  3. Dec 30, 2009 #2

    Ranger Mike

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    a lot a variables here..like are the piston rings moly or cast iron?
    what is the piston to cylinder clearance? what end gap do the rings have? What kind of lubricant is used?
    what kind of heat is generated?
    about the only way to get a good guess is to pull the piston / ring assembly through the cylinder and measure the drag with a scale..like a fish scale to see how many pounds it takes to do this and you may get an estimae of the drag
  4. Dec 30, 2009 #3
    Cheers for the reply,

    Currently the piston ring is EN24T and is flame hardened as it was the easiest and quickest way to do it.

    The piston ring is to be used in a hydraulic radial pump with the in cylinder pressure reaching 400bar. I assumed at this pressure the oil film thickness would be virtually zero due to the squeeze effect. From what I have read it is different to the IC engine rings where the pressure is a lot lower.

    Virtually no heat produced due to the fully flooded conditions.

    So there is no equation I can use that takes into account a minimal film thickness to work out the drag. Could I possibly do a reynolds equation simplification to work out the shear force?

    How come the end gap makes a difference? I would have thought that it only makes a difference to the axial leakage.
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