| 摘要 |
PROBLEM TO BE SOLVED: To suppress a cup seal from being damaged by well chamfering an inner circumferential part of a surface on a cylinder hole opening side of a seal groove, and to improve a workability by simplifying a working of a chamfering part.SOLUTION: The first seal groove 13 is formed in an inner circumferential surface of the cylinder hole 3 to fit a first cup seal 11 therein, and includes a bottom surface of the seal groove in a cylinder hole circumferential direction, a surface on a cylinder hole bottom part side, a surface on the cylinder hole opening side, and a seal groove opening opened to a plunger side. On an inner circumferential part of the surface on the cylinder hole opening side, a chamfered part having an R-shaped part that is chamfered in an R-shape continued to the inner circumferential part of the surface of the cylinder hole opening side and a tapered part that is chamfered in a taper shape so that its diameter on the cylinder hole opening side is gradually reduced in its diameter from an end part on the cylinder hole opening part side of the R-shaped part toward the inner circumferential surface of the cylinder hole 3 is formed. The first seal groove 13 is cut by using a cutting tool integrally including a seal groove forming blade and a chamfered part cutting blade. |
