SpudFiles

Considering that 1/2'' PVC is rated ~750 PSI, is it safe to build a stirrup pump out of that? Because, I found a couple of threads for stirrups and it seems most require welding, which I don't have tools/knowledge of.

Compressing air generates heat as a byproduct...heat is not so friendly to plastic. I will not suggest that you use pvc.

Would suggest you invest in a propane torch kit...check with harbour freight.

Youtube will have some tutorials on sweating copper. (soldering copper)

When you go higher than the 'maximum' pressure of a fridge compressor, does it just stop or will it break?

As you build up pressure on the output side, you eventually get to the point where your compressor can't compress the air on its output side any more. It will keep trying, but it won't generate any more pressure - you can't go higher than its maximum pressure*.

The compressor itself won't stop when it gets to its maximum, it will keep on trying, and as a result it will generate more and more heat; this will eventually (rapidly) cause the thermal cutoff to kick in and stop the compressor, hopefully before it burns itself out.

* in fact, it's not a hard pressure limit, rather a differential in pressure between input and output side.

I have maxed my fridgy out twice I think, and it simply stalled. It will not start again until the pressure on the output side is relieved. It still runs fine to this day. Perhaps some compressors behave differently under too high of pressure. Maybe mine survived because it reached such high pressure so quickly. A very small volume was compressed to over 500 psi in about one second before it pooped out.