Why pressure and not Vaccum?

[AJ71DUSTER]

I have a holley red pump on my duster i notice today when i went to put gas in it the tank it had a lot of pressure. it pushed the cap to the second latch when I losen the gap, so first ? why would the tank have pressure? it would seam that the tank would have Vaccum instead with the electic pump drawing fuel from the tank. second ? why pressure?


Thanks

 

[green1]

The ambient temp expanded it?

 

[b5demon]

are you running a return line back to the tank?

 

[AJ71DUSTER]

I know that it was hot (84) for April up here thats hot. lol but i never had that much pressure before, the pumps been on now for 2yrs, I'm not running a return line should I ? , also theres a vent line that runs to the front of the car would that not stop the pressure build up in the tanks ?

Thanks

 

[Tony Fields]

Make sure your vent is working. Mine was creating pressure which finally cracked the tank. Found the steel vent tube plugged up near the fill tube
entry.