Abstract: In a nozzle dam assembly wherein a flange ring is affixed around a circular nozzle opening in a chamber wall, a support frame spans and is in non-threaded connection with the ring by releasable pins which carry under tension any load on the frame directed axially out of the nozzle into the chamber, and a circular dam with a sealing diaphragm disposed over it is attachable to the frame with its rim within the nozzle so that inflatable peripheral sealing means on the diaphragm effect the desired seal of the nozzle independent of the aforementioned axial load.