GB734685A - Improvements in or relating to sealing devices between two relatively movable members - Google Patents

Abstract

734,685. Stuffing-box substitutes; turbines. BRISTOL AEROPLANE CO., Ltd. May 27, 1953 [June 3, 1952], No. 13996/52. Classes 110 (3) and 122 (5). A sealing device for use in power machines operated by compressible fluid pressure comprises maintaining between zero and a maximum dimension a peripheral gap located between two members movable towards and away from one another and separating a zone of high pressure P (high) from a zone of low pressure P (low) by providing (a) a pair of mutually opposed peripheral surfaces on the members defining the gap which converges from the high pressure to the low pressure zone; (b) means for urging the members together with a force which is less than P (high) times the projected area of the opposed surfaces in a direction normal to the force and is not less than the force exerted on the projected area when the gap is open to its maximum dimension ; and (c) means to control the force as a function of P (high) such that the force does not increase due to closure of the gap. An annular piston 4 slidably supported on piston rings 36 in a cylinder 35 formed in a compressor housing 31 has a face 7 separated from an opposed face 6 on the compressor rotor 30 by a gap 8 converging from the higher pressure P (high) to the lower pressure P (low) side of the piston 4 which is urged toward the rotor 30 by fluid admitted from the high-pressure side to the cylinder 35 through a passage 11 and discharged therefrom to the low-pressure side through a nozzle 12, preferably " choked " so that the pressure behind the piston is independent of P (low). The piston 4 is urged away from the rotor 30 by a force equal to the annular area of the face 7 multiplied by the mean pressure in the gap 8 which pressure increases or decreases as the gap decreases or increases ; the gap is thus automatically maintained between predetermined limits. In a modification the cylinder 35 is replaced by a flexible bellows secured to the piston and the housing and the pressure may be admitted to the interior of the bellows from the high-pressure side P (high) through a conduit having its inlet end close to the face 6 to form an entry port therewith which decreases in size as the gap 8 diminishes and thereby produces a fall in the pressure in the bellows. In a further modification the cylinder 35 is formed by a pair of concentric flexible rings attached to the housing and in sliding contact with the piston 4 and having axial slots therein to act as inlet and discharge passages to the space behind the piston.