Abstract: A tool for use in the repair of fluid conduits or pipes prevents fluid flow along the interior surface of the pipe, while allowing flow through a central bypass tube. The tube also serves to support an expandable plug which is axially compressed by a concentric compression tube surrounding the bypass tube. As the compression tube axially compresses the plug, the plug is forced to expand radially due to the flexible nature of the center section wall and the air entrapped therein. As no great amount of pressure is trapped behind the plug due to the communication of the pipe with the outside environment through the bypass tube, relatively low forces may be used in the actuation of the tool. Moreover, the thin wall or membrane of the center section of the plug permits a relatively wide range of expansion, allowing a single plug to be used in a wide variety of pipe sizes. The tool is particularly suited to use with copper water pipes, but is adaptable to virtually any type of fluid conduit or pipe.