The valve lets air pass but not fluid. This keeps fuel from spewing out of the fuel cell vent in the case of an accident or rollover.
The pump is mounted as low as possible in the chassis in relation to the fuel cell to reduce the stress caused by forcing the pump to self-prime all the time. The fuel filter is just above the pump.
Note the extensive use of high-quality AN components and lines throughout the car’s plumbing. This reduces the likelihood of failure in the other major area of DNF’s: a car’s plumbing. With top notch and properly installed plumbing and wiring, reliability greatly increases.