Pump shaft sleeve<\/p><\/div>\n

Pump shafts are usually protected from erosion, corrosion, and wear at seal\u00a0 chambers,\u00a0 leakage\u00a0 joints,\u00a0 internal\u00a0 bearings,\u00a0 and\u00a0 in\u00a0 the\u00a0 waterways\u00a0 by renewable\u00a0 sleeves. The\u00a0 most\u00a0 common\u00a0 shaft\u00a0 sleeve\u00a0 function\u00a0 is\u00a0 that\u00a0 of protecting the shaft from wear at packing and mechanical seals. Shaft sleeves serving other functions are given specific names to indicate their purpose. For example,\u00a0 a\u00a0 shaft\u00a0 sleeve\u00a0 used\u00a0 between\u00a0 two\u00a0 multistage\u00a0 pump impellers\u00a0 in\u00a0 conjunction\u00a0 with\u00a0 the\u00a0 interstage\u00a0 bushing\u00a0 to\u00a0 form\u00a0 an\u00a0 interstage leakage joint is called an interstage.<\/p>\n

In medium-size centrifugal \u00a0pumps\u00a0 with\u00a0 two\u00a0 external\u00a0 bearings\u00a0 on opposite\u00a0 sides\u00a0 of\u00a0 the\u00a0 casing\u00a0 (the\u00a0 common\u00a0 double-suction\u00a0 and\u00a0 multistage varieties), the favoured shaft sleeve construction uses an external shaft nut to hold the sleeve in an axial position against the impeller hub.Sleeve\u00a0 rotation\u00a0 is\u00a0 prevented\u00a0 by\u00a0 a\u00a0 key,\u00a0 usually\u00a0 an\u00a0 extension\u00a0 of\u00a0 the impeller key. The axial thrust of the impeller is transmitted through the sleeve to the external shaft nut.In larger high-head pumps, a high axial load on the sleeve\u00a0 is\u00a0 possible\u00a0 and\u00a0 a\u00a0 design\u00a0 similar\u00a0 to\u00a0 that\u00a0 shown\u00a0 in\u00a0 Figure\u00a0 1\u00a0 may\u00a0 be preferred. This design has the advantages of simplicity and ease of assembly and maintenance.\u00a0 It also provides space for a large seal chamber and cartridge-type mechanical seals. When shaft sleeve nuts are used to retain the sleeves and impellers axially, they are usually manufactured with right- and left-hand threads.\u00a0 The friction\u00a0 of the\u00a0 pumpage and\u00a0 inadvertent contact\u00a0 with stationary parts or bushings will tend to tighten the nuts against the sleeve and impeller\u00a0 hub\u00a0 (rather\u00a0 than\u00a0 loosen\u00a0 them).\u00a0 Usually,\u00a0 the\u00a0 shaft\u00a0 sleeves\u00a0 utilize extended impeller keys to prevent rotation.<\/p>\n

Some manufacturers favour the sleeve, in which the impeller end of the sleeve\u00a0 is\u00a0 threaded\u00a0 and\u00a0 screwed\u00a0 to\u00a0 a\u00a0 matching\u00a0 thread\u00a0 on\u00a0 the\u00a0 shaft.\u00a0 A\u00a0 key cannot be used with this type of sleeve, and right- and left-hand threads are substituted so that the frictional grip of the packing on the sleeve will tighten it against the impeller hub. As a safety precaution, the external shaft nuts and the sleeve itself use set screws for a locking device. In pumps with overhung impellers,\u00a0 various\u00a0 types\u00a0 of\u00a0 sleeves\u00a0 are\u00a0 used.\u00a0 Most\u00a0 pumps\u00a0 use\u00a0 mechanical seals,\u00a0 and\u00a0 the\u00a0 shaft\u00a0 sleeve\u00a0 is\u00a0 usually\u00a0 a\u00a0 part\u00a0 of\u00a0 the\u00a0 mechanical\u00a0 seal\u00a0 package supplied by the seal manufacturer.<\/p>\n

Many\u00a0 mechanical\u00a0 seals\u00a0 are\u00a0 of\u00a0 the\u00a0 cartridge\u00a0 design,\u00a0 which\u00a0 is\u00a0 set\u00a0 and may be bench-tested for leakage prior to installation in the pump.<\/p>\n

For\u00a0 overhung\u00a0 impeller\u00a0 pumps\u00a0 that\u00a0 utilize\u00a0 packing\u00a0 for\u00a0 sealing,\u00a0 the packing\u00a0 sleeves\u00a0 generally\u00a0 extend\u00a0 from\u00a0 the\u00a0 impeller\u00a0 hub\u00a0 through\u00a0 the\u00a0 seal chambers (or stuffing boxes) to protect the pump shaft from wear. If\u00a0 a\u00a0 hook-type sleeve is\u00a0 used,\u00a0 the\u00a0 hook\u00a0 part\u00a0 of\u00a0 the sleeve is\u00a0 clamped between the impeller and a shaft shoulder to maintain the axial position of the sleeve.<\/p>\n

A hook-type sleeve used to be popular for overhung impeller pumps that operate at high temperatures because it is clamped at the impeller end and the rest of the sleeve is free to expand axially with temperature changes. But with\u00a0 the\u00a0 increased\u00a0 use\u00a0 of\u00a0 cartridge-type\u00a0 mechanical\u00a0 seals,\u00a0 the\u00a0 use\u00a0 of\u00a0 hooktype sleeves is diminishing.<\/p>\n

In\u00a0 designs\u00a0 with\u00a0 a\u00a0 metal-to-metal\u00a0 joint\u00a0 between\u00a0 the\u00a0 sleeve\u00a0 and\u00a0 the impeller hub or shaft nut, a sealing device is required between the sleeve and the\u00a0 shaft\u00a0 to\u00a0 prevent\u00a0 leakage.\u00a0 Pumped\u00a0 liquid\u00a0 can\u00a0 leak\u00a0 into\u00a0 the\u00a0 clearance between the shaft and the sleeve when operating under a positive suction head and air can leak into the pump when operating under a negative suction head. This seal can be accomplished by means of an O-ring, or a flat gasket. For high temperature services, the sealing device must be either acceptable for the temperature to which it will be exposed, or it must be located outside the high temperature liquid environment. According to an alternative design used for some high-temperature\u00a0 process pumps, the\u00a0 contact surface of the\u00a0 hook-type sleeve and the shaft is ground at a 45-degree angle to form a metal-to-metal seal.\u00a0 That\u00a0 end\u00a0 of\u00a0 the\u00a0 sleeve\u00a0 is\u00a0 locked,\u00a0 but\u00a0 the\u00a0 other\u00a0 is\u00a0 free\u00a0 to\u00a0 expand\u00a0 with temperature\u00a0 changes. When\u00a0 O-rings\u00a0 are\u00a0 used,\u00a0 any\u00a0 sealing\u00a0 surfaces\u00a0 must\u00a0 be properly finished to ensure a positive seal is achieved.<\/p>\n

All bores and changes in diameter over which O-rings must be passed should be properly radiused and chamfered to protect against damage during assembly. Guidelines for assembly dimensions and surface finish criteria are always listed in O-ring manufacturers\u2019 catalogs.<\/p>\n