Our first home made fueler used the same pump and we ran it right from a 12 V gel cel...no problems at all until we tryi to fill the taxi tank in series with the main tank...then we have to pulse the pump for 20 or 30 seconds and wait for the bulging main tank to subside..... This would kinda support the small vent theory...
However, we did put an automotive fuel filter on the output line of the pump, so this would reduce the flow somewhat....

I'm glad I have one of those overpriced UATs though..I never considered the fuel pressure going through these things...

our new pumps run on 7.2 volts.