If the section AFTER the FINAL ball valve or solenoid goes to the atmosphere there is no need for 80. No pressure is built up. Do you have the name of the inspector? If so, send it to me off list. The inspection team answers directly to me and if they did indeed tell you that 80 is required on a pipe that is essentially open at one end, all of the time, this is wrong and I need to correct that. Perhaps I haven't make myself clear to my team. The only exception would be if the final pipe is ALSO structural in design and must support a great deal of weight, but that is very rare.
Those who think they can and those who think they can't are both right.