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Canned Rotor Pumps

Canned rotor pumps are Glandless Pumps whose rotating components within the canned motor run in the liquid being handled by the pump.

Design
Shaft sealing by means of a stuffing box or a mechanical seal required for conventional pumps thus becomes obsolete. The pumped liquid serves as a lubricant for the bearings (sleeve bearings) and as a coolant to the motor compartment. A can serves to seal the so-called wet space to atmosphere and to the motor compartment. The can, of a mean wall thickness of only 0.1 to 0.3 mm, is made of magnetic highly alloyed steel. Generally, the can is statically sealed by means of O-rings.

Funktion / Feature
The advantage of this construction is primarily the totally maintenance-free operation. No alignment or dis-mantling of sealing components but a reliable and faultfree run operation during the entire operation.

The quietness of operation of this design is remarkable, this being due to the dampening effect of the water in which the rotating parts move and, most particularly, to the sleeve bearing support of the rotor. Thus any noise normally originating from ball or roller bearings are fully eliminated .
Not only the quiet operation but also the service life span and the defect susceptibility are decisively influ-enced by this component.

The bearing arrangement is one of the essential constructional features of canned rotor pumps. The mate-rial combination of the bearings is, apart from the actual design of the bearings, of decisive importance for the operational reliability of the pump. The following combinations have eventually prevailed in practice:

  • ceramic shaft/ceramic bearing
  • hardened stainless steel shaft/carbon bearings


The ceramic bearing arrangement, shaft and bearings of equal material, actually contradicts traditional bearing theory. On the basis of the extremely hard and brittle qualities of the material aluminium oxide cera-mic it has, conditional on optimum lubrication, a very low wear rate. Any lack of proper lubrication such as due to air accumulation or vapour formation on overheating can however lead to locking of the rotor. In addition, there is the relatively high breaking susceptibility on mechanical stress ie. transport shock or by de-locking jammed rotors.

The two-component bearing arrangement - hardened stainless steel shaft/carbon bearing - on the other hand offers extremely good dry-run or emergency run characteristics respectively of metal impregnated carbon bearings. Additionally, there is the proverbial breaking safety of the hardened steel shaft on shock and jolts.

Operating Reliability
Based on decade-long practice with millions of pumps, a life expectancy from approx. 40 000 to 70 000 operating hours under normal conditions and depending on the type of pump has been established as a statistical mean value. This relates to an average running period from 8 to 12 years under normal heating conditions. The optimum functional capabilities of this design is accentuated by the fact that not a few only canned rotor pumps have been running more than 15 to 20 years (more than 100 000 operating hours) free of defects and without maintenance.
Today’s generation canned rotor pumps on the whole feature multi-speed characteristics of their drive motors. This speed variation can be effected manually by means of integrated selector switches or automatically by suitable control gear.



Also see:
Basic Pump Designs
Glanded (Dry-Motor) Pump





Subject area PUMP TYPES


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