Harry: I don't remember the exact numbers but you want to keep the max pressure to 100 psi for inside air temp of 150 degrees F to keep the plastic lines from bursting from gas pressure. Butane is low pressure about 70 psi and propane is higher about 200 psi at 150 degrees.
The valves use gas pressure to help them close, and too high a pressure
may keep them from opening but not freeze as in cold.
Darryl Usher