To have an idea of "how long it will last" I can give you my experience.
I have a compressor with a 2L Bottle, at 4 bar, with my V4, at full throttle, it last about 30 seconds, if I reduce the pressure at 1 bar to the engine, it can last 2 min, but at 1 bar there is not enough power to do somthing.
And I want to say that this engine is one of the best I have ever made, it's not leaking, the pistons and the switches are exellent, this engine is very efficient.
(I m sorry, I m not very good in english so....)