| 摘要 |
PURPOSE:To lower the sealing pressure at a sealing section that is kept in contact with external liquid, by providing a pressure loading means capable of keeping the internal pressure in a space to be sealed always higher than the external pressure even if the depth of excavation is varied. CONSTITUTION:A space between an upper seal 55 and a lower seal 56 for a turning shaft is communicated to a space A in a housing 42, which has a bellows type pressure equalizer 57 exposed to the outside together with a cover 58. Further, an orifice like a variable restriction, a sequence valve 28, and a pressure loading means such as a self-sealing joint 33 taking the pressure loss into consideration are provided at proper portions of a drain piping 26 which is extended from a drain outlet port of a hydraulic motor 21 to an oil tank 16C. With such an arrangement, it is enabled to keep the internal pressure of a space C to be sealed always higher than the external pressure. |
