Rollover valve - Vent valve 

Ideal to avoid too much pressure or a vacuum in the fuel tank.

The valve is attached at an angle of over 90 degrees and thus ensures that you have free ventilation from your petrol tank. If the car then rolls over, the steel ball that is inside it will roll over the vent and ensure that the petrol cannot escape. There are  different ways of installing an "overturning valve". You can for example install it with AN nipples, where the thread is long and can reach through the car's undercarriage. A breather valve is also used because it cannot be avoided that the fuel will vaporize and thereby expand. If you have not fitted a breather valve you can get way too much pressure in the tank and it can "bulge out". It can also be a problem not to have venting, since when you use fuel a vacuum will form in the tank, which can lead to it collapsing.