second spring means mounted on said rod, compressed between said flange and an abutment on said rod for urging said shutter means to close said first pipe when said {HEAD ~ third pipe contacts} with {TAIL ~ said vessel} and is lowered thereby, and to close said second pipe when said third pipe moves toward its raised position, so as to bring selectively said shutter means into close contact with either one of said first and second pipes, without causing any clearance therebetween, and thereby ensuring the prevention of leakage of the exhaust gas 
second spring means mounted on said rod , compressed between said flange and an abutment on said rod for urging said shutter means to close said first pipe when said { HEAD ~ third pipe contacts } with { TAIL ~ said vessel } and is lowered thereby , and to close said second pipe when said third pipe moves toward its raised position , so as to bring selectively said shutter means into close contact with either one of said first and second pipes , without causing any clearance therebetween , and thereby ensuring the prevention of leakage of the exhaust gas
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