Patent ID: 6641742
Filing Date: 2003-11-04
Classification: B01D

Abstract:
A liquid filter comprising a housing having an inlet and an outlet, a filter element in said housing and having an upstream outer face communicating with said inlet, and a downstream inner face communicating with said outlet, said filter element filtering liquid passing therethrough from said outer face to said inner face, said housing having a sidewall which defines with said outer face an inlet chamber therebetween having an upper section and a lower section, such that as liquid enters said inlet chamber from said inlet, gas in said liquid rises to said upper section of said inlet chamber, a low level of liquid indicating a low pressure drop non-plugged condition of said filter element, the higher the level of said liquid in said inlet chamber the greater the pressure drop across said filter element and the greater the plugging of said filter element, a change interval plugging indicator in said housing comprising a gas trap and pressure responsive release mechanism trapping said gas in said upper section of said inlet chamber until a designated release pressure is reached, corresponding to a desired terminal pressure, to prevent premature plugging indication otherwise indicated by rising liquid level in said inlet chamber, wherein said change interval plugging indicator comprises an outer wrap around said outer face of said filter element in said upper section of said inlet chamber and blocking gas flow therethrough at least at pressures below said designated release pressure, wherein said outer wrap has a lower end which defines a lower end of said upper section of said inlet chamber and an upper end of said lower section of said inlet chamber, and wherein said gas is trapped in said upper section of said inlet chamber when liquid in said inlet chamber rises above said lower end of said outer wrap, and wherein said outer wrap is a porous member wetted by said liquid such that capillary pressure in said porous member blocks gas flow therethrough below said designated release pressure, and such that pressure above said designated release pressure overcomes said capillary pressure and gas passes through said outer wrap.