Patent ID: 7552744

Claim:
A pressure-relief valve for an oil-filled transformer or tap changer having a casing, the valve comprising: a flange formed with a throughgoing port; means for securing the flange to the casing; a seal surrounding the port; a spring plate spaced outward from the port; a rigid post secured directly to the spring plate and to the flange and fixing the spring plate relative to the flange; a valve body between the spring plate and the flange and displaceable between a closed position engaging the seal and closing the port and an open position spaced outward from the port and permitting flow out of the casing through the port; a spring having an outer end bearing against the spring plate and an inner end bearing against the valve body to urge the valve body into the closed position, whereby when pressure in the casing exceeds a predetermined limit the valve body is pushed out and fluid in the casing can pass into the housing and thence out of the housing; a cup-shaped housing engaged over and covering the valve body, spring plate, post, and spring, the housing having an end wall spaced from the flange and a side wall projecting from the end wall toward the casing and forming a rim, the spring plate subdividing an interior of the housing into an inner compartment holding the valve body and spring and into which the port opens and a separate outer compartment between the spring plate and the end wall, the side wall being formed at the inner compartment with a throughgoing vent opening, whereby the spring plate blocks fluid flow from the inner compartment to the outer compartment; means for removably securing the rim directly to the flange, whereby removal of the housing exposes the spring plate, post, valve body, and spring; a rigid feedthrough plate fixed to the flange and extending to the outer compartment, the housing side wall being fitted around the feedthrough plate; and a cable extending from a switch inside the outer compartment through the feedthrough plate to outside the compartment.