rear surface the cup shaped wall 38 is preferably formed as single piece or as several pieces solidly joined together and is slidingly moveable in a direction a about the piston chamber flanged end 26 a chamber seal 46 preferably prevents air from flowing between the flanged end 26 and an internally extending portion 48 of the sleeve body 42 when the cup shaped wall 38 is in a fully opened position as best seen in fig3 the sleeve body 42 is preferably cylindrical but may be of any shape to conform to a shape of the flanged end 26 and the flat rear surface 40 although moveable the cup shaped wall 38 is preferably held in the fully closed position by a first pawl 50 the first pawl 50 is configured as well known in the art to be preferably located directly or by a linkage in association with a housing not shown of the tools described above the first pawl 50 is preferably also a beveled rod or any solid shape known in the art which is moveable to hold the cup shaped wall 38 firmly when in the fully closed position the flat rear surface 40 of the cup.