Liquid filter

A liquid filter comprising

• a cup-shaped housing with a liquid inlet and a liquid outlet in communication with a discharge chamber of said filter;
• a filter element sealingly disposed in said housing between the inlet and the outlet, and
• a one-piece barrier membrane disposed adjacent the opening of the cup-shaped housing so that the liquid inlet and the liquid outlet can be closed by the barrier membrane, wherein
• the barrier membrane includes a circular connecting plate having a first return flow barrier arranged on the radially outer edge thereof and a concentric second return flow barrier arranged radially inwardly thereof,
• the connecting plate is provided with connecting elements for detachably connecting the barrier membrane to an end disk of the filter element or to a cover plate, and
• the concentric second return flow barrier includes an outlet seal valve having a duckbill configuration, said duckbill constructed as a flexible tube continuation extending from said connecting plate into said discharge chamber, said flexible tube forming a pair of tilted, opposing, generally flat members converging to form a self-closing slit, said slit configured to sealably close said liquid outlet,
• wherein curved sidewalls of said flexible tube are operable to tension said flat members to maintain closure of said slit,
• wherein the duckbill is directed towards the interior of the filter element,
• wherein the duckbill is configured to be mechanically opened during installation.