Tanks which are vented to the atmosphere emit hydrocarbons. Prior to 2011, all marine fuel tanks were open-vented to the atmosphere. The new requirements require that emissions be controlled by either a carbon canister or a sealed pressure system.
The pressure relief system is also known as a closed system, while the canister is often referred to as an open system. The pressure relief system enables momentary release of tank pressure within operating specifications to meet emissions requirements. Click the button below for more detail about pressure relief systems.
In a canister system, the vapors flow through the tank during a diurnal cycle, dropping hydrocarbons in the canister on the way out. The idea is that the hydrocarbons will stay put and be picked up by the incoming flow and put back into the system, where they will be burned up in the combustion cycle of the engine. Click the button below for more detail about carbon canister systems.
Diurnal emissions are a form of evaporative emissions that occur when fluctuations in ambient temperatures over the course of a day cause fuel tanks to release fuel vapors. Diurnal emissions also occur when the engine is not operating. For more information about diurnal emissions, click here.
Moeller works with every major diurnal component manufacturer to deliver a range of EPA-compliant and NMMA-certified options for each builder’s unique build requirement. In 2015 we introduced our own line of valves and direct fill. For more information about Moeller diurnal components, click here.