Piston ring and booster pump

A piston ring to be attached to a piston, the piston being formed in a cylindrical shape along an axis and configured to reciprocate along the axis to compress a fluid, the piston ring comprising:

• a low-pressure side ring inserted in a groove formed in an outer circumferential face of the piston, formed in an annular shape extending in a circumferential direction about the axis, and having a low-pressure side abutment;
• and
• a high-pressure side ring inserted in the groove, formed in an annular shape extending in the circumferential direction, and having a high-pressure side abutment,
• wherein the low-pressure side ring and the high-pressure side ring are arranged stacked in a direction along the axis so that the high-pressure side ring is closer to a fluid to be compressed,
• wherein a low-pressure side rotation restriction part configured to restrict rotation in the circumferential direction relative to the piston is formed on the low-pressure side ring, the low-pressure side rotation restriction part being arranged at a position different from the low-pressure side abutment in the circumferential direction,
• wherein a high-pressure side rotation restriction part configured to restrict rotation in the circumferential direction relative to the piston and a low-pressure side protrusion protruding toward the low-pressure side ring and inserted in the low-pressure side abutment are formed on the high-pressure side ring, the high-pressure side rotation restriction part and the low-pressure side protrusion being arranged at a position different from the high-pressure side abutment in the circumferential direction, and
• wherein the low-pressure side protrusion is inserted in the low-pressure side abutment with clearances being provided in both sides in the circumferential direction between the low-pressure side ring and the low-pressure side protrusion.