Abstract: The invention provides A pneumatically sealed rapidly attachable and demountable A-clamp type yoke for filling compressed gas cylinders having valves designed for interengagement for A-clamp type yokes, the A-clamp type yoke comprising an A-clamp type yoke housing, an opening in the housing for receiving the spout of a tank valve, a stepped cylindrical bore in the housing connected to the opening, a stepped cylindrical piston-like element held in and guided for reciprocal movement in the stepped cylindrical bore, the piston-like element being provided with a through-going conduit for gas flow and with an annular surface surrounding the outlet of the conduit and sized for sealing abutment against a sealing surface of the spout of the tank valve inserted in the opening, a compression spring in the stepped cylindrical bore urging the piston-like element and the annular surface thereof into engagement with the spout, and means of attachment of the yoke to a source hose, the means including a conduit leading to th