Plumbing air pressure test?

Great point brought forward JandL differentiating between hydraulic and air pressure.  I have just finished blowing out irrigation lines on 3 golf courses over the last 3 days and while we maintain 120 - 125 lbs of water pressure in the lines during the summer using the 375 CFM air compressor we may get up to 36 - 38 lbs air pressure in those same lines while blowing out/purging water out of the lines.  When water is purged and air comes out of the sprinkler heads, the sound is something like a jet ready for take-off.  This is especially true at the end when we open a 2" line to let the air out quickly so we can disconnect the hose, this takes about 12-15 minutes.  When the air comes out you better have on some really good ear protection otherwise you will end of going deaf or ruining your hearing, the sound of the air escaping is deafening.

Most use a regulator.  They are inexpensive and easily put in line to the water inlet.  I don't know that they are needed in most campgrounds but they don't hurt.

I have an adjustable water regulator, think most are preset 45-50, which is ok. Those not adjustable are at 45 I think. I maintain my pancake air compressor as close to 30 when doing winterization. That works. I have never air pressurized with all closed. Currently have no water leaks.

"I think my pressure regulator I use is rated for 50 psi."

Are you talking about your water pressure regulator? My water pressure regulator is also set to 50 PSI. The safety issue is when you use air to pressure something

Be careful when doing an air pressure test

From Charlotte Pipe, Air Testing of Plumbing Piping Systems, Technical Bulletin #15811
“Air testing – of any piping system – is not a system capability issue; it is
a life-safety issue. A pipe segment withstands air pressure in exactly the
same manner as it withstands hydrostatic pressure; the physics don’t
change.
Water is not compressible and cannot store energy through compression,
so under these scenarios nothing threatening will occur. Air is
compressible and will store energy under compression which will release
explosively, possibly throwing shards of pipe, test plugs, fittings or debris.”