Patent GB-622394-A (GB)
Title: Improvements in and relating to centrifugal compressors
IPC: F04D29/16
Filed: 1947-03-18
Abstract: 622,394. Centrifugal compressors. BRITISH THOMSON-HOUSTON CO., Ltd. March 18, 1947, No. 7469. Convention date, March 19, 1946. [Class 110(i)] A multi-stage centrifugal compressor comprises two impellers, or two sets of passages in a single impeller, arranged back-to-back, with the diffusers for the two stages formed on either side of a central plate to which the respective outlet scrolls are attached. The inter-stage passage is of U form, and its cross-section, which decreases progressively, is flattened at the bend to avoid the fluid leaving the inner wall. Leakage from the high-pressure to the low-pressure stage is prevented by making the second stage impeller of slightly larger diameter than the first and arranging for the promotion of an opposing pressure-gradient in the clearance space between the stages by providing auxiliary blades on the impeller periphery between the stages or by making the circumferential clearance between impeller and stator increase towards the second stage to give a diffuser effect. Casings.-In the arrangement shown, the casing is formed in four parts: a right-hand bearing support and inlet chamber 2, with lateral entrance, is adapted to carry a generator or other auxiliary on a flange 42 and to be secured in any desired angular position to the next portion 3, which provides three walls of the first stage outlet scroll and the first half of the inter-stage passage; a central plate 4, forming the fourth wall of the first stage scroll, has the diffusers 20, 30 of the two stages formed on either side of it, and a fourth portion 5, with a bearing for the left-hand end of the shaft, provides the second half of the interstage passage, the second stage inlet chamber 27, and, with the plate 4, the discharge scroll 32, which has a tangential outlet pipe 33; the casing portion 5 has a flange 41 by which the compressor is supported, for example from the gear casing of an engine driving it. The inter-stage passage, of which the sectional area progressively decreases, bends through two right-angles in the casing parts 3, 5 respectively, passing through an aperture in the plate 4; in order to avoid separation of the fluid from the inner wall of the bends, the cross-section of the passage at this part is much narrowed radially, and elongated in a direction perpendicular to the plane of the bend, from the square section which it has where it is in communication with the diffuser 20 as shown. Multiple-way impellers; leakage, preventing. - In the arrangement shown, a unitary impeller 7 with two separate shrouded bladed passages 10, 11 arranged back-to-back, is used, but two separate single-way impellers may be employed and the shrouding may be rendered unnecessary by shaping the casing walls to lie close to the impeller. The impeller is made somewhat larger at the high-pressure stage than at the low-pressure stage, to reduce the possibility of leakage between the stages; in addition, the clearance between impeller and stator may be made larger at the larger diameter, so that pressure will build up in this clearance, or small blades may be provided on the impeller periphery between the stages to opposite any flow from left to right. Lubricant from the bearings is kept out of the fluid pumped by sealing means at 16, which may be supplemented by labyrinth packing as at 17.