one direction accordingly in various embodiments the second locking portion 75 is locked to the locking protrusion 95 with the second spring 84 compressed by the second shaft 71 therefore the first and second clamps 50 and 70 can clamp the body 10 and the cover 30 by means of the elastic force of the first and second springs 64 and 84 in the process described above accordingly in various embodiments when backfire pressure above a predetermined level is exerted between the body 10 and the cover 30 as shown in fig7 a and 7b the cover 30 is lifted up by the backfire pressure against the elastic force of the first and second springs 64 and 84 such that a gap g is defined between the body 10 and the cover 30 therefore the backfire pressure is released through the gap g between the body 10 and the cover 30 and when the backfire pressure drops below predetermined pressure the cover 30 is recombined with the body 10 by the elastic force of the first and second springs 64 and 84 meanwhile in various embodiments the user holds the grip 76 of the second clamp 70 and lifts up and turns the second shaft 71 in one direction in order.