Patent 7563084 was granted and assigned to Daikin Industries, Ltd. on July, 2009 by the United States Patent and Trademark Office.
A cylinder body is sandwiched between a front head and a rear head. A high pressure port is formed in the front head. A roller of a piston is configured such that top and bottom end surfaces thereof have different widths. The roller is arranged such that one of the top and bottom end surfaces having a larger width faces the front head 7.