PURPOSE: To provide proper clearance between a partition plate and a partition plate groove when the cylinder body is to be fixed to an enclosed container, by forming the partition plate groove in such a way that its width increases toward the center of the cylinder.

CONSTITUTION: When the cylinder body 6 is to be processed, a partition plate groove 14 is so provided radially from the axis of cylinder 6a in such a manner that its width increases toward said axis. This angle of width increase shall correspond to the angle of narrowing of partition plate groove generated when the cylinder body 6 is fixed to an enclosed container 1 by welding or pressure fitting. This will secure a certain required clearance between the partition plate and the groove even after the cylinder is installed at said enclosed container.