Pressure relief venting lid

A lid assembly for closing an opening in a wall of a container and regulating pressure in the container, said lid assembly comprising:

• a cover,
• means for removably securing said cover to the container in sealed relation to said opening,
• said cover having a fill port,
• a vent cap for said fill port,
• said vent cap comprising a support plate and a port closure plate,
• means mounting said port closure plate to said support plate in generally parallel relation thereto with said support plate overlying and protecting said port closure plate,
• means for supporting said vent cap on said cover for movement from a first position in which said port closure plate sealingly engages said fill port to a second position in which said port closure plate completely disengages said fill port,
• said mounting means for said port closure plate comprising a plurality of spring units pressing said port closure plate into sealing engagement with said fill port when said vent cap is in said first position but yieldable in response to an excess of pressure in the container to permit said port closure plate to at least partially disengage said fill port and thereby vent the container,
• said fill port comprising an annular lip extending from said cover toward said port closure plate and terminating in an annular sealing edge,
• said port closure plate having a laterally outer peripheral portion defining an annular channel opening toward said port closure plate and terminating in an annular flange extending toward said cover in overlapped, telescoping relation with said lip when said vent cap is in said first position, and
• an annular sealing ring carried by said port closure plate in said channel,
• said sealing ring sealingly engaging said sealing edge of said lip when said vent cap is in said first position and said annular flange, because of its telescoping relation with said lip, preventing lateral shifting of said port closure plate and resultant breaking of the seal between said sealing edge of said lip and said sealing ring,
• said port closure plate having a central main body portion which is semi-spherically shaped and convex away from said support plate to enhance the capacity of the port closure plate to withstand internal container pressure and hydraulic shock without flexing or distorting.