Pulp bleaching tower pressure relief hatch

Claim 1

A hatch assembly for a wood pulp bleaching vessel comprising a cylindrical coaming secured to said vessel around a vent port opening, a flange secured to said coaming having a planar face disposed perpendicular to the axis of said coaming, a hinged cover for said vent port pivotally secured to said coaming for swinging about a hinge axis parallel with said coaming flange face, a cylindrical plug portion of said cover projecting from a planar flange portion of said cover for insertion into an internal bore of said coaming when said cover flange is adjacently parallel with said coaming flange, a first O-ring seating groove in the face of said coaming flange around the circumference of said bore, a second O-ring seating groove in said cover flange opposite of said first seating groove, and a third O-ring seating groove in and around a cylindrical surface of said plug, an annular clearance space extending radially between said plug cylindrical surface and the internal bore of said coaming and axially between said coaming flange face plane and said third O-ring seating groove, a first vinyl tube O-ring seated in and projecting from said first seating groove into said second seating groove, and a second vinyl tube O-ring seated in and projecting from said third O-ring groove, said second O-ring tube having a wall thickness substantially the same as the radial dimension of said annular clearance space.