An oil filled electrical equipment includes an assembly for oil filling and hermetically sealing the electrical equipment. The assembly includes a cylindrical bellow mounted on a plate of the electrical equipment with one or more fittings. The bellow provides pressure and volume compensation in the electrical equipment. The bellow includes a cylinder with a plurality of convolutions for expanding and contracting to provide the compensation. The bellow further includes two covers attached with the cylinder at two ends of the cylinder. Each cover includes a cylindrical part that is open at a first end and closed at a second end. The first end terminates at a circular face for mounting the cover on a convolution at a corresponding end of the cylinder. The second end includes an opening for oil filling and hermetically sealing the electrical equipment, and mounting the bellow on the plate.