Some "sprinkler" valves are rated for more than 300 psi, it just depends on what type you have. If the regulator is only putting out 140 psi, I would suggest using it to pressurise big pneumatics that you don't want to fill with a hand pump, or to use it as a constant air supply for a strafer if the regulator's flow rate is high enough.
Jack: I know that you really want to see a 500 psi cloud, so I will build one by the end of September, just for you. (no, really, I will)
