To highly precisely measure bubbles in the whole system by moving a hydraulic fluid to a bubble separator having a bubble separating part in its lower part and a bubble amount measuring part in its upper part, and by rising separatingly bubbles up to measure the bubbles collected in the bubble amount measuring part.
The vicinity of one end part of a main passage 27 is made to communicate with the vicinity of the other end part by a by-pass passage, Y-type opening and closing valves 24, 25 are arranged respectively in the vicinities of both end parts in the by-pass passage, and a bubble separator A (B, C) is arranged between both the valves 24, 25 of the by-pass passage. Two X-type opening and closing valves 22, 23 are arranged with a space between the vicinity of one end part of the main passage 27 and the vicinity of the other end part, a bubble amount measuring part 34 is formed in an upper part of the bubble separator A (B, C), and a bubble separating part 36 is formed in its lower part.
KYO KOKEI
KAN HYO