Piston Rings Keep Blowing Out.

It sounds like you've done a thorough job of troubleshooting the problem, and it's possible that the piston ring is not the only issue. Here are a few other things that could be causing the compressor to blow the piston ring:

A blown head gasket. This would allow combustion gases to enter the compressor cylinder, which could cause the piston ring to blow.

A cracked cylinder sleeve. This would also allow combustion gases to enter the cylinder, and could also cause the piston ring to blow.

A defective connecting rod. This could cause the piston to wobble or vibrate, which could put extra stress on the piston ring and cause it to blow.

If you've replaced the piston ring twice and the compressor is still blowing the ring, it's likely that one of these other issues is the cause. You may need to take the compressor to a qualified technician to have it diagnosed and repaired.

Here are some additional steps you can take to troubleshoot the problem:

Check the compression in the compressor cylinder. If the compression is low, it could be a sign of a blown head gasket, cracked cylinder sleeve, or defective connecting rod.

Inspect the piston ring for damage. If the ring is damaged, it will need to be replaced.

Inspect the cylinder sleeve for damage. If the sleeve is damaged, it will need to be replaced.

Inspect the connecting rod for damage. If the connecting rod is damaged, it will need to be replaced.

Once you've identified the source of the problem, you can take the necessary steps to repair the compressor.