| 摘要 |
A vertically moving body (24) for adjusting the position of a valve plate is obtained from a first ring-shaped body (24A1) and a second ring-shaped body (24A2). The second ring-shaped body (24A2) is connected to the first ring-shaped body (24A1) in a freely detachable manner by means of projections (40) that engage with engaging parts and non-engaging parts (38). The connection to the first ring-shaped body (24A1) can be released and the second ring-shaped body taken out of the casing (12) by aligning the projections (40) with the non-engaging parts (38). Only when the second ring-shaped body (24A2) is moved, by the driving of a drive source (20) to a position at which frictional resistance with the surroundings is released, is displacement allowed and alignment of the projections (40) with the non-engaging parts (38) possible. |
