PURPOSE: To prevent air from invading into an auxiliary reservoir by providing the auxiliary reservoir so as to enclose, the main reservoir of a hydraulic unit, and providing an integrated assembly consisting of a first chamber communicated with the oil supplying port of the auxiliary reservoir, a second chamber communicated with a main reservoir, and a ring body having an oil passage communicated with both chambers.

CONSTITUTION: The hydraulic unit (Y) of an oil pressure rush adjustor in a valve system is provided with a main reservoir 52 communicated with a high pressure chamber 60. A bucket (X) is installed around the hydraulic unit (Y), and an auxiliary reservoir 40 communicated with the main reservoir 52 is formed by a sleeve 30 and an oil. supplying port 2X A ring body 11 is stored integratedly in the auxiliary reservoir 40 to form a first chamber 12 and a second chamber 16 on the inner circumference of the bucket (X), and an oil passage 10 communicated with the chambers 12, 16. Even if an oil surface is reduced till the lowest value in the oil passage 10, the oil surface is not reduced till the level where the oil passage 10 is closed. The second chamber 16 and the main reservoir 52 are filled up with working oil, and air is not sucked into the high pressure chamber 60.