Patent ID: 8186688

Claim:
A rotating shaft seal device comprised of a seal case mounted on a housing, and having plural seals arranged in a peripheral space of the shaft between the seal case and the rotating shaft disposed in first, second and third stages in an axial direction between the seal case and the rotating shaft passing through an inner periphery of the seal case; wherein the first-stage seal is on an inner side of the machine and the third-stage seal is on an outer side of the machine and both have a contact-type mechanical seal structure in which a rotational seal element and a stationary seal element are in close sliding contact with each other; and the second stage seal is located intermediate the first and third stages and has a non-contact-type mechanical seal structure in which the rotational seal element and the stationary seal element are kept by dynamic pressure so as not to be in contact with each other; and a seal fluid under higher pressure than the pressure of fluid inside the machine is supplied from feed port(s) into a first annular space surrounded by that portion of the seal case extending from said first-stage seal to the second-stage seal.