Estimating shear loss from a piston ring

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SUMMARY

The discussion focuses on estimating shear loss from an EN24T metal piston ring in a hydraulic radial pump operating at an in-cylinder pressure of 400 bar. Key variables affecting shear loss include piston speed, friction coefficient, piston-to-cylinder clearance, and lubricant type. The user suggests measuring drag directly using a scale for accurate estimation, as conventional equations may not apply due to minimal oil film thickness under high pressure. The conversation also touches on the impact of end gap on axial leakage.

PREREQUISITES
  • Understanding of hydraulic pump mechanics
  • Knowledge of material properties, specifically EN24T steel
  • Familiarity with friction coefficients in mechanical systems
  • Basic principles of fluid dynamics, particularly Reynolds equation
NEXT STEPS
  • Research methods for measuring drag in hydraulic systems
  • Study the application of Reynolds equation in low film thickness scenarios
  • Explore the effects of piston ring materials on performance
  • Investigate the relationship between end gap and axial leakage in hydraulic pumps
USEFUL FOR

Mechanical engineers, hydraulic system designers, and anyone involved in optimizing piston ring performance in high-pressure applications.

g0ggs123
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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.

Cheers

(Updated:

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

Any help would be much appreciated.)
 
Last edited:
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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
 
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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