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UPRE Unistress Piston Ring Expander

The Unistress Piston Ring Expander subject the ring to four forces as indicated and therefore to a uniform moment throughout, except at the ends where it decreases rectilinearly towards zero.


Constant moment means constant stress which again means the lowest stress possible for a desired opening of the ring. Each UPRE is provided with a stop, limiting the deformation of the ring to the minimum required to slip it over the piston diameter.


As a result one may count on a UPRE always being used once it has been procured. The UPRE are delivered adjusted and ready for use for any type of piston ring and diameter upward of 130 mm.

Additional Details

A UPRE has the advantage of making change of the piston rings much easier. Even the biggest rings can easily be changed.

  • Type 1, piston rings 100-250 mm
  • Type 2, piston rings 250-380 mm
  • Type 3, piston rings 380-600 mm
  • Type 4, piston rings 600-980 mm
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