Apparatus for developing diazo type film

In a diazo type developing apparatus wherein diazo sensitized exposed film is developed by exposure to ammonia gas which apparatus includes a chamber for receiving exposed film, the chamber having at least one ammonia gas entry port and one ammonia gas exit port, the chamber having a height and length sufficient to receive the film and having a minimum width sufficient to permit circulation of the ammonia gas therein about the film, means for heating the chamber to a predetermined temperature, means for circulating ammonia gas in the chamber including a closed container of ammonium hydroxide liquid coupled between the ammonia gas entry port and the ammonia gas exit port, the circulating means further including an input to the container disposed below the level of the liquid and an output from the container disposed above the level of the liquid and coupled to the gas entry port of the chamber, the circulating means still further including a pump coupled between the gas exit port of the chamber and the input to the container for bubbling ammonia gas through the liquid and circulating it between the chamber and the container;

• the improvement comprising means in said chamber for preventing exit port closure by the film when the pressure thereat is reduced during operation of the apparatus.