As referred to above, reference numeral designates bellows that is expansible in the left and right directions, the both left and {HEAD ~ right side edge portions} of {TAIL ~ this bellows} are fixedly secured to the top edge portions of the above described left and right side walls and , and the tip end portion of the above referred pressurized air feed pipe is mounted to a central portion of the same bellows  
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As referred to above , reference numeral designates bellows that is expansible in the left and right directions , the both left and { HEAD ~ right side edge portions } of { TAIL ~ this bellows } are fixedly secured to the top edge portions of the above described left and right side walls and , and the tip end portion of the above referred pressurized air feed pipe is mounted to a central portion of the same bellows
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