GB820348A - Means for ensuring fluid-tightness between two gases separated by a wall through which passes a rotating shaft - Google Patents

Abstract

820,348. Stuffing-box substitutes. SOC. ALSACIENNE DE CONSTRUCTIONS MECANIQUES. July 23, 1957 [Feb. 12, 1957], No. 23344/57. Class 122 (5). Sealing means for a rotary shaft 1 passing through a wall 2 separating two gases comprises a sleeve 3 closely surrounding the shaft and secured in fluid-tight manner to the wall and forming around the shaft a central annular chamber 4 in which terminate two helical grooves 5a, 5b of opposite hand, the grooves being formed either in the sleeve, as shown, or in the shaft and having a depth which progressively decreases away from the chamber, auxiliary packing means, such as the sealing ring 9, being provided to prevent leakage when the shaft is at rest and arranged to come into operation when or just before the shaft comes to rest. In operation, when the shaft 1 rotates, the helical grooves 5a, 5b operate as pumps to form a vacuum in the chamber 4 and oppose leakage of gas from each side of the wall. The sealing ring 9, which may be of polytetrafluoroethylene, closely surrounds the shaft and has a conical exterior surface which is forced against a corresponding conical seating 8 on a plate 6 secured to the wall, the ring being thereby pressed on to the shaft, by a control mechanism when the shaft stops or its speed falls below a predetermined value. The ring is moved axially out of contact with the seat when the shaft begins to rotate or when its speed exceeds the predetermined value. The internal surface of the sleeve and the portion of the shaft surrounded thereby may be bi-conical with a maximum diameter in the vicinity of the chamber 4. The invention is described as applied to sealing the shafts of rotary compressors circulating hexafluoride of uranium in a nuclear reactor, the wall 2 separating the hexafluoride of uranium at low pressure from nitrogen at substantially the same pressure. As an alternative to the sealing ring 9, leakage of gas from one side of the wall to the other when the shaft is stationary may be prevented by a vacuum pump coupled to the chamber 4 and arranged to operate as soon as the shaft stops or when its speed falls below a predetermined value.