movement exhaust port 26 will reduce the pressure below the piston to atmospheric pressure so that the inlet pressure acting on the upper end of the piston will cause the piston to rapidly move downwardly in the embodiment of the invention shown in fig2 housing 40 comprises outer cylindrical member 40a and inner cylindrical member or sleeve 40b the housing 40a may be provided with a tapered hollow recess 60 located at a lower region thereof and a circular opening 61 to facilitate mounting of the vibrator piston 42 is located in bore 43 of the housing and moves relative to inner sleeve member 40b outer inlet port 44 is connected to a source of air under pressure not shown and supplies annular chamber 46 between the outer and inner members of the housing with air under pressure inner inlet port 48 supplies air to the inside of the housing to flow through passages 49 and 50 in piston 42 and in the manner described above cause the piston to reciprocate in the bore of the housing outlet passages 52a and 52b and 54a and 54b function in the same manner as described above in connection with outlet passages 24.