Vented Vs Non Vented Fuel Cap

If that tube is not present then you need a vented gas cap.

Vented vs non vented fuel cap.

Emissions gas caps have a built in pressure relief valve that will only vent to the atmosphere if the pressure gets too high. If your tank has a vent then you will need a non vented cap. Both styles of caps provide vacuum relief. Vented caps only vent one way into the tank to allow air in as the fuel is used to prevent a vacuum from occurring.

Gasoline systems have been running non vented caps for quite a while due to the emissions requirements. The vented gas cap has a one way release valve that is pressure activated. A non vented cap is just that no venting at all and will not let air in or out so unless you have an eec tank or other vent setup elsewhere you ll have some issues. Gas caps have not been vented since the introduction of evaporative emission controls smog control on cars many years ago.

Vented gas logs produce carbon monoxide emissions so your fireplace must have a chimney or flue. Look at the front of tank at the axle for a u shaped metal vent tube about one inch in diameter. When the pressure reaches a certain point defined by so many pounds per square inch the valve opens by a very small amount relieving some of the pressure. Gas fireplaces come in two configurations.

All modern vehicles use a non vented cap. Ventless logs do not put off these emissions so no chimney or flue is needed and the heat is more likely to stay in your space. The vented gas cap is designed to vent small amounts of air into the car gas tank line.