MECHANICAL SEAL

PURPOSE:To decrease a load applied to sealing end faces of a seal and spread a range of its limit use, by providing a subsealed chamber independently of a main sealed chamber at the back side of one of the sealing rings and arranging internal pressure of said subsealed chamber lower than sealed fluid pressure in the main sealed chamber by a prescribed level. CONSTITUTION:A main sealed chamber 18 is formed appearing to sealing end faces 4a, 5a in a seal housing 1, and a sealed liquid flow passage 19, communicated to the main sealed chamber 18, is formed in the seal housing 1. While a subsealed chamber 20 is formed independently of the main sealed chamber 18 appearing at the back side of a stationary sealing ring 4, of both sealing rings 4, 5, by a fixed member 7, sealing retainer 6 and O-rings 9, 21. Then the subsealed chamber 20 is controlled so that its internal pressure may be lower than pressure of sealed liquid in the main sealed chamber 18 through a pressure adjusting liquid passage 22 formed in the housing 1 and the fixed member 7.