Sealing device for the driver member of a pneumatically operated driving tool for fasteners

A pneumatically operated driving tool, comprising a driver member, which has a forward end, a working cylinder, a working piston slidably arranged in said working cylinder for movement between an upper and a lower dead center, a resilient stop member having an opening and an inner face, the stop member defining the lower dead center of the working piston movement, the driving member being secured to said working piston and extending through the opening of said stop member, further comprising a control valve, a trigger and a first cylinder space above said working piston, wherein the control valve is actuated by the trigger to alternatively connect the first cylinder space with a source of compressed air and to atmosphere, a piston return space, which contains air, in communication with a second cylinder space below said working piston, into which the piston return space air is displaced while a working stroke of the working piston is performed, upon which the displaced piston return space air returns said working piston into the upper dead center when the first cylinder space is vented to atmosphere by means of said control valve, the driving tool still further comprising a plate-shaped mouth tool having an extension portion and a driving channel for guiding said driver member, a magazine opening into said driving channel, and a vent passage extending from the inner face of said stop member along said driving channel towards the forward end of said driver member, the vent passage venting the second cylinder space below said working piston to atmosphere until the downwardly moving driver member closes off said vent passage, said stop member comprising a recess facing said mouth tool, said recess sealingly receiving the extension portion of said mouth tool in a resiliently biased engagement between said recess and said extension portion.