Abstract: A sealing unit effects a connection between a loading boom and a manhole on a tank car. Liquids are delivered through the boom into the tank car. Vapors displaced from the tank are transmitted, through the sealing unit, to conduit means, which enable disposal of the vapors without contaminating the atmosphere. The unit comprises an upper plate which rests on the manhole. A sleeve is connected at its upper end to the upper plate and, at its lower end, to a lower plate. A pneumatic motor is actuated to draw the lower plate upwardly. When this occurs, the sleeve is bulged outwardly into sealing engagement with the manhole. Column springs are provided to assure that the central portion of the sleeve will bulge outwardly and provide sealing engagement with manholes of different diameters.