An air cannon is used for removing adhering and accumulating bulk material in silos, heat exchangers, lines and the like with the aid of blasts of air. The necessary compressed air is stored in a pressure container (1) and passes, via the outlet valve (3) and a discharge nozzle (11) adjoining the latter, into the region of the adhering bulk material and detaches the latter. The outlet valve (3) has a valve housing (9) and a piston (19) which is guided longitudinally in a guide (18) and is acted upon, at the rear, by a closing pressure which can be lowered abruptly. The piston (19) has, at its front side facing the discharge nozzle (11), an annular valve sealing surface (25), inside which, when the valve is closed, the pressure in the discharge nozzle (11) acts and outside which the pressure prevailing in the pressure container acts.
