Device for circulation of a gaseous and/or liquid fluid through at least one solid particle bed equipped with at least one bypass means acting on at least one part of said fluid through at least one part of a solid particle bed, said bypass means comprising: - a pipe whose top end discharges above the upper surface of the catalyst bed and whose bottom end discharges into the solid particle bed, said end being equipped with a means preventing the passage of the solid particles into said pipe, and - a valve, comprising: a) a widened tubular part having the shape of a truncated cone, whose orifice with the smallest cross-section is connected to one end of the pipe of the bypass device, b) a movable piece having the shape of a ball or a truncated cone, mounted in said widened tubular part, consisting of a plate mounted to be able to move around one axis on one end of the pipe of the bypass means in such a manner as to allow displacement between a closed position and a maximum open position, the positioning of said plate being dependent on the fluid flow rate in the bypass means, and c) a return means acting on the movable piece to move it toward the closed position in which the movable piece blocks the orifice of the widened tubular part with the smallest cross-section, the return means acts by the force of gravity of the movable piece. - a pipe whose top end discharges above the upper surface of the catalyst bed and whose bottom end discharges into the solid particle bed, said end being equipped with a means preventing the passage of the solid particles into said pipe, and - a valve, comprising: a) a widened tubular part having the shape of a truncated cone, whose orifice with the smallest cross-section is connected to one end of the pipe of the bypass device, b) a movable piece having the shape of a ball or a truncated cone, mounted in said widened tubular part, consisting of a plate mounted to be able to move around one axis on one end of the pipe of the bypass means in such a manner as to allow displacement between a closed position and a maximum open position, the positioning of said plate being dependent on the fluid flow rate in the bypass means, and c) a return means acting on the movable piece to move it toward the closed position in which the movable piece blocks the orifice of the widened tubular part with the smallest cross-section, the return means acts by the force of gravity of the movable piece. a) a widened tubular part having the shape of a truncated cone, whose orifice with the smallest cross-section is connected to one end of the pipe of the bypass device, b) a movable piece having the shape of a ball or a truncated cone, mounted in said widened tubular part, consisting of a plate mounted to be able to move around one axis on one end of the pipe of the bypass means in such a manner as to allow displacement between a closed position and a maximum open position, the positioning of said plate being dependent on the fluid flow rate in the bypass means, and c) a return means acting on the movable piece to move it toward the closed position in which the movable piece blocks the orifice of the widened tubular part with the smallest cross-section, the return means acts by the force of gravity of the movable piece.