A properly built vacuum truck tank in good condition (see articles HERE and HERE for internal tank inspections) can handle full vacuum and, unless a certified pressure vessel is legally limited to 14.9 PSI, we recommend limiting your tank to no more than 8-9 PSI.
Your vacuum pump is protected by your pressure relief valve. A vane pump is cooled by the air that travels through it, which is why you need the vacuum relief: to allow cool atmospheric air into the pump to keep it cool at higher vacuum levels.
Without a properly functioning vacuum relief valve, your vane pump will overheat. Generally, we recommend a vacuum relief valve to begin opening at around 15-16 inches of mercury so as to not build vacuum any higher than 18-20 inches when fully open.
A blower pump generally does not require a vacuum relief, since it has a ballast port to introduce cooling air to the blower.
It is important to have a vacuum truck tank that is properly engineered, properly built, and properly maintained.
The action item here for any vacuum truck owner is to regularly check the function of your vacuum and pressure relief valves and adjust them to proper levels. See video HERE for how to adjust your vacuum relief valve, and HERE for how to adjust your pressure relief valve.