Piston Rings in Reciprocating Compressor

You forget that he can copy a BAD design. Copying is an ART not everybody can copy. There is a very good example, France and UK developed the first (and till now single) supersonic commercial plane(the Concorde). Russians obtained by "black" activity the plans and build exactly the same but it crashed after one or 2 test flights.

Now for the rings. The function is double and there are complex constrains to respect.

As function one can mention sealing and lubrication. As constrains there is the tribology of the contacts ring-piston and ring-cylinder which are different. the ring-piston is loaded by the pressure and generates a surface fatigue and the ring-cylinder has as well sealing as wear resistance. Laws of tribology indicate how to choose the hardness of ring with respect to cylinder.

A lot of informations are available and only those who do not have the knowledge of tribology can recommend to start all research from the scrap. The problem can be solved on paper far enough to obtain an almost final result if the different parameters as pressure, velocity, roughness, oil viscosity, hardness (material) aso are considered from the very start. of course experimental work has to be done since theory is always a simplification of reality and cannot take all details into consideration but it helps to reduce the amount of tests which are always the most expensive part of development.

In pistons where pressure changes sides (as in the picture) the problem is more complex due to the pumping effect at every stroke end but basically the theory and practice is the same.

The number of rings depends on the pressure and other functional parameters. Their position depends on the basic design single acting or double acting. Not all rings are identical.