PURPOSE:To block invasion of a cooling liquid and foreign matters by providing a straight tube in which the head is held between the top of a housing and the tip of a push rod, the skirt is fixed to the end surface of a guide member, and the body is made slidable to a push rod, and recessed line grooves are formed on the inner surface. CONSTITUTION:In a rubber-seal straight tube 1, its head 2 is held between the top 5 of a housing 4 and the tip of a push rod 6, and its skirt 8 is fixed to the end surface of a guide member 9. And its body 7 can slide to the push rod 6, and a necessary number of recessed line grooves are formed at its inner surface. In such a composition, the rubber-seal straight tube 1 is guided by the push rod 6, and moves rearward when a return spring 17 pushes, being developed freely to form a bellows, and the sliding part between the push rod 6 of a thermostat and the guide member 9 is covered airtight by the flexible bellows. As a result, invasion of a cooling liquid and foreign matters to the inside can be blocked perfectly.
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