Chemical Technology October 2015

Pump selection and application guidelines – Part 2 by Neetin Ghaisas, ME, PEng, Director of Design Engineering and Rotating Equipment Group Leader at Fluor Canada, Calgary, Alberta, Canada

A standard set of considerations and best industry practices that Rotating Equipment Engineers apply in the selection of various types of pumps and their auxiliaries, is described. Typical services and limiting operating conditions of centrifugal and positive displacement pumps are included to aid in the selection process. Part 1 appeared in the August 2015 issue.

Lubrication of pump bearings Standard methods of lubrication are: A Grease B Wet sump with oil ring or oil flinger C Purge (wet) or Pure (dry sump) oil mist D Forced oil

• Most calcium, barium and lithium based greases have an operating temperature range of -30 to +120 ºC. Organic thickener grease such as alkoxyfluoroether oil based grease have a higher range; - 40 to + 250 ºC. Greases with solid lubricants are normally used for mixed/boundary friction. During operation, thickeners in grease together with wear particles gradually form abrasive paste which in turn, may induce further wearing of bearing elements. • When sealed bearings are required, engineers should specify “Sealed for bearing life” greased bearings. Use of sealed greased bearings is usually limited to operating temperatures not exceeding 100 ºC. Oil lubrication • Wet sump with oil flinger is the preferred method of lubrication for horizontal pumps. • Pump bearing housings should have non-contacting, laby- rinth type seals as a standard to preclude atmospheric contaminants from entering the housings. For pumps installed outdoors in dirty environments (loose fly ash, soot, dust, sand etc.), magnetic type bearing isolator seals should be considered to achieve positive isolation of bearing housings from the environment, especially when the pump is not in operation.

E Bearings lubricated by pumped fluid as in the case of magnetic drive pumps and vertical line shaft pumps.

1. The first three types of lubrication methods are used for anti-friction bearings. 2. Forced or pressure oil lubrication is applied to hydrody- namic bearings. 3. Oil lubrication is the preferred method over grease lubrication. Minimum specification requirements and limiting conditions grease lubrication • A Greased bearings should be used when oiled bearings cannot be used; such as in cryogenic services where the fluid temperature may be close to pour point of the mineral oils or where access is limited or where leakage of oil can be hazardous or surrounding atmosphere is laden with soot, dust, or ash particles.

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Chemical Technology • October 2015