Estimating shear loss from a piston ring

AI Thread Summary
Calculating shear loss from a metal piston ring in a hydraulic pump requires consideration of several variables, including piston ring material, clearance, end gap, lubricant type, and generated heat. The piston ring in question is EN24T and flame-hardened, operating under high pressure of 400 bar, which may lead to minimal oil film thickness. Users suggest measuring drag directly by pulling the piston/ring assembly through the cylinder for an accurate estimate. There is uncertainty about using Reynolds equation simplifications for shear force calculations given the conditions. The end gap impacts not only axial leakage but also overall performance, which is crucial in high-pressure applications.
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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.)
 
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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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