| 摘要 |
<p>PROBLEM TO BE SOLVED: To prolong the lifetime of a seal ring by preventing the push-in of a seal ring into a liquid return hole. SOLUTION: A seal ring 13 for prohibiting the movement of liquid between pressure chambers 10, 12 and a reservoir has a first ring 45, which is made of the elastic material and which is bonded to the periphery of pistons 9, 11, and a second ring 46, which is made of the material harder than that of the first ring 45 and which slide-contacts with a side peripheral inner wall 4c of a cylinder hole 4, and the seal ring 13 is provided with a liquid supplying passage, which by-passes a part sealed buy both the rings 45, 46 so as to communicate the pressure chambers 10, 12 with the reservoir, and provided with a supplementary valve 30 for allowing the only liquid movement from the reservoir to the pressure chambers 10, 12 through the liquid supplying passage.</p> |
