Shaft sealing apparatus

摘要

A shaft sealing apparatus capable of preventing gases vaporized from a gas seal or purge fluid from leaking outside before a pressure switch operates due to a pressure rise resulting from a fluid leakage from a mechanical seal. The apparatus comprises a seal casing and a rotary shaft passing through the former and having a mechanical seal A and a dry gas seal B mounted thereon in line with each other to provide purge fluid areas C therebetween. With this arrangement, a purge fluid is supplied to one of the purge fluid areas through a supply line having an orifice OA and the supplied purge fluid and a leaked part of a target fluid to be sealed are released outside from the other purge fluid area through a relief line having an orifice OB. The relief line is provided with a bypass line with an electromagnetic valve and a pressure switch and bypassing the orifice OB. In this case, the purge fluid supply pressure P1, the preset pressure P2 between the orifices OA and OB, the pressure P3 in the area from the orifice OB to outside and the pressure switch operating pressure Ps satisfy the relationships of P1>Ps>P2>P3.