GB929790A - Improvements in or relating to centrifugal pumps - Google Patents

Abstract

929,790. Centrifugal pumps. TAIT MANUFACTURING CO. July 5, 1960, No. 23484/60. Class 110 (1). A centrifugal pump comprises an impeller having a hub forming a bearing surface rotatable within a bearing, at least the hub being formed from a synthetic resin having the property of swelling in water by a predetermined amount, the outer diameter of the bearing surface being sufficiently less than the inner diameter of the bearing when the pump is first placed in service that a substantial running clearance is provided for the passage of sand or other abrasive material present in the water, and the clearance becoming reduced, after the swelling has taken place, to a valve providing proper bearing support. In the case of a pump put into service in a new well, the high concentration of abrasive material usually encountered for the first few hours or days of operation in a new well can pass through the initial substantial bearing clearances without causing undue wear. The impellers 21, Fig. 6, of a multistage submersible pump are made of a nylon resin which swells in water by 1 to 3% of its initial dimensions, the resin desirably containing molybdenum disulphide to control the swelling and act as a lubricant. Each impeller may be cast in two pieces, one including the hub 30 and back shroud 33 and the other including the front shroud 35 and vanes 36, the pieces being secured together by means of integral rivets formed on each vane and passing through holes in the back shroud. Each impeller 21, together with a diffuser 22, operates within a casing 23, the thrust on the impeller normally being taken by engagement of a boss 40 with a bearing surface 45 on the casing 23. In the event of reversal of the thrust, the thrust is instead taken by a bearing surface 53 on a bush 51, which may be of stainless steel, in the centre of the diffuser 22. The bush 51 forms a radial bearing for hub sleeve 34, the clearance between the sleeve and bush being initially large, for the reason stated above, before the sleeve has become swollen by the water. Each impeller 21 is splined to the pump shaft 20 with freedom to float axially, and the shaft has no bearings other than the bushes 51. Each diffuser 22 is cast from a plastics material and comprises a disc 50 formed with a cylindrical rim 55. The liquid discharged by each impeller 21 is guided axially by generally helical fins 56, Fig. 7, projecting outwardly from the rim 55 of the adjacent diffuser 22, each fin 56 ending in a shoulder 57, Figs. 7 and 8, which engages within a notch 47 in the surrounding casing 23. The liquid is then guided radially inwardly towards the next impeller by means of diffuser vanes 61, formed on the back of the diffuser 22. The outer portion 62 of each vane 61 is cylindrically curved and merges with the rim 55.