Abstract: This fluid lock permits transiting an object between different fluid pressure through a transiting hole in a wall separating a higher fluid pressure side from a lower fluid pressure side on opposite sides of the wall; has higher and lower fluid pressure doors, each hinged for pivotal movement between an open position for permitting transiting through the hole from one to the other pressure side and a closed position for sealing the opening; and has a transiting container formed between the doors in closed position, and closely form fitting the transiting object, for minimizing the loss of fluid between the sides during transiting the object through the hole.