Vacuum truck implosion - GIF

[Frank S]

Back in the early nineties at a Ford Truck dealer I worked at I was given a job to repair the fuel tanks. It was a F800 with a 429 gas engine. Both tanks imploded. There was a failure with the evap system. After I replaced a defective vacuum controlled valve instead of replacing the tanks the boss said just pressurize them with air. I'm not doing. The customer drove away with damaged tanks that probably held 10 less gallons between the two.

Fill the tank completely full of liquid then apply 3 to 4 PSI positive pressure and lightly tapping all around the edges of where the tank is collapsed For the Rectangular diesel fuel tanks which were also a step to get in the cab of the truck 5 to 7 PSI is sometimes required
7PSI is enough to ruin a motorcycle tank don't ask me how I know