Abstract: A transformer is provided that utilizes a substantially fully integral, generally outwardly convex casing or tank for enclosing an electrical transformer in a dielectric environment. The casing has fully integral side and top and bottom end walls, and has an open portion in its top end wall of sufficient size to serve both as a positive low to high pressure release and a maintenance hand hole. An easily inserted and removed cover assembly employs an operating stem, a domed cover member, a clamping member, a nut carrying bracket member and a spring that may be adjusted to a desired pressure relief setting by rotating the stem in one direction. Rotation of the stem in an opposite direction releases its clamping setting and loosens the parts of the cover assembly in such a manner as to permit it to be easily and quickly removed from the open portion by tilting it with respect to and out of the open portion.