GB817396A - Seals for sealing rotatable members passing through partitions - Google Patents

Abstract

817,396. Stuffing-box substitutes. NAPIER & SON Ltd., D. Feb. 22, 1957 [Feb. 23, 1956], No. 5703/56. Class 122 (5). A seal for sealing a rotatable member 12, Fig. 1, where it passes through a partition 11 between two spaces containing two gases which must not be allowed to mix comprises a flexibly-mounted ring 14 having an annular sealing face which is separated by a barrier sealing gas from an opposing sealing face 17 on a collar or flange 16 on the rotatable member 12. The barrier gas is supplied, at a higher pressure than that of either of the gases to be kept apart, through a duct 26 to a space 25 on one side of the ring 14 and then through a passage 27 in the ring to an annular recess 18 in the sealing face of the ring. The annular space 25 is closed in one side by a diaphragm 15 which also flexibly supports the ring and allows it limited axial movement; the annular recess 18 is bounded by inrer and outer annular lands 19, 20. The pressure of the barrier gas, which may be compressed air, is adjusted so that very small clearances are maintained between the surface 17 and the lands 19, 20, the ring 14 constituting, in effect, a gas thrust-bearing. In the modification shown in Fig. 2, a carbon annulus 13 carried by a disc 31 forms the rotatable sealing element opposing a fixed face 38. The disc 31 has a rearward projection 32 which is flexibly mounted by bonding it to a rubber ring 33 having its outer periphery bonded to a surrounding ring 34 carried by a collar 35 secured to the shaft 12. A clearance 36 between the shaft 12 and disc 31 permits the sealed gas (e.g. contaminated carbon dioxide) in the space 10 to enter a narrow annular recess 37 so that the pressure of this gas tends to bring the face of the carbon annulus and the fixed face 38 into contact. The annular space between two circular lands 39, 40 on the face of the annulus 13 is supplied from a duct 42 and outlet 41 with compressed air which tends to separate the annulus from the face 38. The air leaks past the land 39 to atmosphere and past the land 40 to an escape port 44 in the face 38. A further gas (e.g. pure carbon. dioxide) is admitted from a duct 48 to a channel 47 disposed between two arrays of circular lands 45, 46 on the annulus so as to serve as the barrier sealing gas. By adjusting the pressure of the compressed-air to suit the prevailing pressure of the sealed gas, the axial clearance between the surface 38 and the lands on the carbon sealing face can be maintained practically constant and very small, thereby reducing the leakage of gas from the channel 47 and enabling the excess pressure of the barrier gas to be kept low. In the event of a failure of gas supply from the channel 47, the pressure of the compressed air alone will not keep the sealing faces 13, 38 apart so that the lands 39, 40 will make contact and will thereby effect a temporary gas-tight seal. The rubber ring 33 may be replaced by two metal bellows-type diaphragms having a bleed passage for the pure carbon dioxide to provide an approximate pressure balance across the diaphragms. In a further modification, the carbon annulus is secured directly on the shaft 12 and the flat surface with which it co-operates is flexibly mounted by a resilient ring in the partition.