Provided is an arrangement for sealing a bellows cylinder in a pressure block of a pressure ring assembly. The bellows cylinder is located in a cavity formed in the pressure block and is operated by hydraulic fluid to give pressure against a contact shoe of a contact shoe ring arranged on the inside of the pressure ring assembly. The bellows cylinder is sealed to the cavity. A sealing bowl is arranged on the bellows on the inner side of the pressure block. The sealing bowl has an essentially flat surface towards the contact shoe and is provided with a side edge extending into the cavity. A circumferential groove containing a gasket ring is on the side wall of the cavity. A flexible sealing ring is arranged around the gasket ring to give tension and pressure on the gasket ring against the side edge of the sealing bowl.