in a radial piston pump , motor , transmission the deep diving or entering piston shoe is utilized and swingably borne in the pivot - bed of the radially reciprocating piston . since deep diving piston shoes have large piston strokes , the shoes pivot in the pistons in large angles . thereby a considerable force - portion of the load on the piston is transfered to the wall between the piston and the cylinder , whereby heretofore short pistons produced occasionally welding and sticking between the cylinder wall and the piston wall . the piston therefore receives radially extending portions , which may extend beyond the medial portions of the piston show and may even enter into the ring groove of the piston stroke actuator ring . thereby a very long guidance of the piston on cylinder wall portions is obtained , which makes the application of effective pressure balancing pockets at correct location between piston wall and cylinder wall possible . an extended piston guide and friction -- less travel of the piston in the cylinder without wearing or sticking is assured .