"Michael Horowitz" wrote in message
...
Someone gave me a Speedaire Model 3Z394 airtank.
I know nothing about its integrity or working pressure.
1. If you own such a model, could you tell me the max safe tank
pressure?

That model was originally powered by a 3/4 hp motor so I would guess it has
a shutoff pressure of 120 psi.

2. How can I determine if the tank (which as some rust on the outside)
still has its integrity?

Only a hydrostatic test can prove the integrity.