Abstract: A drilling rig comprising a plurality of pipes connected in a row, with a drill at the lower end; the rotation transmitting bar or Kelly bar at the top end of the drilling rig must be periodically disconnected so as to install a new pipe section; the invention comprises a valve to seal the upper rotating or Kelly bar when it is disconnected so as to keep the sludge pump primed; the valve comprising a collapsible diaphragm which is forced shut by pressurized fluid to seal the rotating or Kelly bar; and an air escape valve communicating into the row of pipes beneath the sealing valve for effecting removal of air trapped beneath the rotating or Kelly bar valve.