of this port is to equalize the pressure across the upper endcap 24 to prevent bowing or possible fracture of the endcap 24 this is accomplished by in effect allowing a small portion of the unfiltered fluid on the outside of the cartridge to move through the pressure relief aperture 30 to the top of the endcap 24 the purpose is to allow the pressure to equalize across the gasket at the top and to avoid putting undue stresses on the endcap 24 or the axial seal gasket 26 the pressure downstream of the media is always less than the upstream pressure when the filter is flowing fluid this differential pressure can be quite high in cases where the filter is plugged the velocity is high or the fluid is cold and viscous when a pressure relief aperture 30 is provided this pressure is carried to the top of the upper endcap 24 and causes an unbalanced force to be placed on the upper endcap 24 tending to force it into the housing in practicing this aspect of the invention this force is counterbalanced in the housing the unbalanced force is due mainly to the center of the endcap 24 which has the upstream pressure on one side and downstream pressure on the bottom side the unbalanced force is in the downward direction and tries.