The E-Valve prevent water contamination in your fuel caused by humid air entering your tank via the vent hose.
Ethanol blended into today's diesel and gas fuels absorbs water from the air much faster than the fuel itself.
This absorbed water can have devastating, and expensive(!), effects on modern high tech engines.

The E-Valve installs in your fuel tank's air vent hose.
It allows unrestricted air flow while your engine is operating, but seals the tank vent line when your vessel is not in use preventing moisture from entering your tank, and contaminating your fuel, as would otherwise happen.

Protects your valuable marine engine from damage due to water contaminated fuel
Works so well, it is now installed as original equipment on many modern vessels
Seals fuel system when vessel is not in use
Reduces moisture build up in your fuel system
Corrosion resistant construction
Compliant with EPA mandate 40CFR part 1060