The pressure leakage from the back pressure chamber installed at the back side of the movable scroll to the low pressure area can be prevented. This is done by making aligned slots in the front wall and abutment means with side to side widths greater than the diameter of the needle cap body but less than the outside diameter of the needle cap rim. The tool communicates with a controller which can communicate with the tool, and to a display in communication with the tool and the controller. According to preferred aspects of the invention, each bridge is the root of its own multiple spanning tree instance.