Abstract: An assembly for sealing against the escape of gas round a rotary shift where it exits from apparatus containing gas under pressure, such as a compressor, comprising an oil (or other sealing liquid) film seal means arranged where said shaft exits from the body of the apparatus and comprising an annular chamber surrounding said shaft and to be supplied with oil at a pressure above that of said gas in said apparatus, said annular chamber being axially closed by two axially spaced annular elements mounted on said shaft with radial clearance to provide a passage for oil to flow from said chamber between said annular elements and said shaft, and sealing means for preventing escape of gas in the event of a failure of the supply of oil to said annular chamber or stoppage of said apparatus and comprising an outer chamber, an annular piston in said outer chamber in engagement with said shaft through a labyrinth seal, and first and second seals, said first seal being connected with said piston and said second seal being