Pump Shaft Sleeves

 Pump Shaft Sleeves

A shaft sleeve is a cylindrical hollow metal tube placed over the shaft to protect as it passes through the packing. Pump shafts are often protected from erosion, corrosion, and wear at leakage joints, seal chambers, internal bearings and in the waterways by renewable sleeves. The most common shaft sleeve function is that of protecting the shaft from packing wear at the stuffing box. A shaft sleeve used between two multistage pump impellers in conjunction with the inter-stage bushing to form an inter-stage leakage joint is called an inter-stage or distance sleeve.

These are used in single stage pumps. Impeller and sealing gland are not directly  mounted on  shaft.  A  sleeve  is  fitted  between  the  bore  of  the impeller and OD of the shaft and keyed with the shaft i.e. impeller rotate with the sleeve along with the shaft. The wearable part in this type of assembly is the  sleeve,  which  is  far  less  expensive  than  the  shaft.  The  function  of  the impeller sleeves is to protect the shaft from wear and coming in contact with the pumping fluid.

Pump shaft sleeve

Pump shaft sleeve

Pump shafts are usually protected from erosion, corrosion, and wear at seal  chambers,  leakage  joints,  internal  bearings,  and  in  the  waterways  by renewable  sleeves. The  most  common  shaft  sleeve  function  is  that  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,  a  shaft  sleeve  used  between  two  multistage  pump impellers  in  conjunction  with  the  interstage  bushing  to  form  an  interstage leakage joint is called an interstage.

In medium-size centrifugal  pumps  with  two  external  bearings  on opposite  sides  of  the  casing  (the  common  double-suction  and  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  rotation  is  prevented  by  a  key,  usually  an  extension  of  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  is  possible  and  a  design  similar  to  that  shown  in  Figure  1  may  be preferred. This design has the advantages of simplicity and ease of assembly and maintenance.  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.  The friction  of the  pumpage and  inadvertent contact  with stationary parts or bushings will tend to tighten the nuts against the sleeve and impeller  hub  (rather  than  loosen  them).  Usually,  the  shaft  sleeves  utilize extended impeller keys to prevent rotation.

Some manufacturers favour the sleeve, in which the impeller end of the sleeve  is  threaded  and  screwed  to  a  matching  thread  on  the  shaft.  A  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,  various  types  of  sleeves  are  used.  Most  pumps  use  mechanical seals,  and  the  shaft  sleeve  is  usually  a  part  of  the  mechanical  seal  package supplied by the seal manufacturer.

Many  mechanical  seals  are  of  the  cartridge  design,  which  is  set  and may be bench-tested for leakage prior to installation in the pump.

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

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  the  increased  use  of  cartridge-type  mechanical  seals,  the  use  of  hooktype sleeves is diminishing.

In  designs  with  a  metal-to-metal  joint  between  the  sleeve  and  the impeller hub or shaft nut, a sealing device is required between the sleeve and the  shaft  to  prevent  leakage.  Pumped  liquid  can  leak  into  the  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  process pumps, the  contact surface of the  hook-type sleeve and the shaft is ground at a 45-degree angle to form a metal-to-metal seal.  That  end  of  the  sleeve  is  locked,  but  the  other  is  free  to  expand  with temperature  changes. When  O-rings  are  used,  any  sealing  surfaces  must  be properly finished to ensure a positive seal is achieved.

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’ catalogs.

At Global Pumps & Spares, we keep a full range of shaft sleeves in ready stock.
Shaft Sleeves are available for Kirloskar Pumps, KSB Pumps, Beacon Pumps, Mather Platt (Wilo) Pumps, etc
Shaft Sleeve M.O.C. –  EN8, EN19, C.I, S.S 410, S.S 304, S.S 316, Bronze etc.
Manufactured from best quality raw materials, the Pump Shaft Sleeves are available in different grades and sizes as per the needs of our esteemed customers.
More details at http://www.globalpumps.in/shaft-sleeves.html



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