[JFP in PA]

Originally Posted by Mike Billings

I see. Thanks.

At some point above 20psi, the relief on cap pops up.

Does that open the system?

There is a pressure relief on the system which is designed to relieve small pressure excursions above it's preset, but it cannot handle constant high volumes like an air compressor can deliver; people often forget that a decent air compressor can deliver 90 or more cubic feet of air a minuet.