In my clean up of the pump, I found that there is an adjustable relieve valve on the bottom of the intercooler.
Unfortunately the setting screw is loose, so I am not confident that it is set correctly.
I have not found any information on what PSI the valve should be set for.

It took a bit of hunting but found out it is an previous generation Chinook (Rol-Air) K28.
It works well and seems to put out about the specified CFM and pressure.

I have the current generation manual, but would love to find a copy of a manual and parts diagram matching the pump.
It is from 1986.