Fuel tank vent system

Abstract

An apparatus and method vent a fuel tank through an oleophobic membrane. In one embodiment, a pressure relief valve accommodates pressure buildups that may result from use of the oleophobic membrane. In one embodiment, a vacuum relief valve accommodates pressure drops within the fuel tank. that may result from use of the oleophobic membrane.

1 . An apparatus comprising:
 a fuel tank;   a vent conduit extending from an interior of the fuel tank;   an oleophobic membrane across the vent conduit; and   a vacuum relief valve between the interior of the fuel tank and atmosphere.   
     
     
         2 . The apparatus of  claim 1  further comprising a pressure relief valve between the interior of the tank and atmosphere. 
     
     
         3 . The apparatus of  claim 2 , wherein the pressure relief valve is configured to vent out gas from the interior of the fuel tank at a flow rate of between about 30 ccm and 170 ccm up to a pressure within the interior of the tank of 1.2 KPa. 
     
     
         4 . The apparatus of  claim 3 , wherein the fuel tank is configured to supply fuel to an engine configured to operate using an air to fuel ratio within an intended range and wherein the pressure relief valve is configured to vent gas out of the interior of the tank at a flow rate of at least F TMmax  starting at a maximum pressure within the interior of the tank that causes the air to fuel ratio to lie outside the intended range and wherein the flow rate F TMmax  is greater than or equal to the rate of thermal and vapor expansion within the fuel tank due to increasing thermal transients and motion generated vapors. 
     
     
         5 . The apparatus of  claim 2  further comprising a cap incorporating the pressure relief valve. 
     
     
         6 . The apparatus of  claim 5 , wherein the cap incorporates the vacuum relief valve. 
     
     
         7 . The apparatus of  claim 1  further comprising a fuel tank incorporating the pressure relief valve. 
     
     
         8 . The apparatus of  claim 7 , wherein the cap incorporates the vacuum relief valve. 
     
     
         9 . The apparatus of  claim 1 , wherein the cap incorporates the vacuum relief valve. 
     
     
         10 . The apparatus of  claim 1 , wherein the fuel tank has an outer wall incorporating the vacuum relief valve. 
     
     
         11 . The apparatus of  claim 1 , wherein the vacuum relief valve is configured to vent gas into the interior of the fuel tank at a flow rate of at least 25 ccm. 
     
     
         12 . The apparatus of  claim 1  further comprising:
 a second that conduit influence communication with the interior of the fuel tank; and 
 a second oleophobic membrane across the second vent conduit. 
 
     
     
         13 . The apparatus of  claim 1  further comprising a carbon canister connected to the vent conduit on an opposite side of the oleophobic membrane as the fuel tank. 
     
     
         14 . The apparatus of  claim 1 , wherein the vent conduit is connected to an intake system of an engine including the carburetor. 
     
     
         15 . An apparatus comprising:
 a fuel tank;   a vent conduit extending from an interior of the fuel tank;   an oleophobic membrane across the vent conduit;   a pressure relief valve in fluid communication with the interior of the tank; and   a vacuum relief valve between the interior of the fuel tank and atmosphere.   
     
     
         16 . The apparatus of  claim 15 , wherein the pressure relief valve is configured to vent out gas from the interior of the fuel tank at a flow rate of between about 30 ccm and 170 ccm up to a pressure within the interior of the tank of 1.2 KPa. 
     
     
         17 . The apparatus of  claim 15 , wherein the fuel tank is configured to supply fuel to an engine configured to operate using an air to fuel ratio within a range and wherein the pressure relief valve is configured to vent gas out of the interior of the tank at a flow rate of at least F TMmax  starting at a maximum pressure within the interior of the tank that causes the air to fuel ratio to lie outside the range and wherein the flow rate F TMmax  is greater than or equal to the rate of thermal and vapor expansion within the fuel tank due to increasing thermal transients and motion generated vapors. 
     
     
         18 . The apparatus of  claim 15  further comprising a carburetor operatively coupled to the fuel tank and a fuel pump operatively coupled between the fuel tank and the carburetor. 
     
     
         19 . The apparatus of  claim 15  further comprising a cap incorporating at least one of the pressure relief valve and the vacuum relief valve. 
     
     
         20 . A method comprising:
 venting an interior of a fuel tank across an oleophobic membrane to a vapor handling system; and   relieving a vacuum in the fuel tank through a vacuum relief valve.