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Pump Wisdom: Chapter 8: Bearing Housing Protection and Cost Justification

Pumps & Operations

Pump Wisdom: Chapter 8: Bearing Housing Protection and Cost Justification

Explore key facets of centrifugal pump ownership, installation, operation, and troubleshooting

The Second Edition of Pump Wisdom: Essential Centrifugal Pump Knowledge for Operators and Specialists delivers a concise explanation of how pumps function, the design specifications that must be considered before purchasing a pump, and current best practices in lubrication and mechanical seals.

This new edition also contains new startup and surveillance tips for pump operators, as well as repair versus replacement or upgrade considerations for maintenance decision-makers, new condition monitoring guidance for centrifugal pumps, and expanded coverage of operator best practices.

ReadChapter 7: Lubricant Types and Key Properties.

Both oil and air fill the bearing housing. As it either gets warm and expands, or cools and contracts, an interchange of the internal air takes place with the surrounding or ambient air. The interchange is called “breathing.” To stop this breathing and resulting contamination, the breather vents on the housings should be plugged and suitable bearing protector seals (see Note below) installed where the shaft protrudes through the housing.

Note: The terms bearing housing protector seal, bearing protector seal, and bearing isolator are used interchangeably.

Inexpensive lip seals are sometimes used for sealing at the bearing housing, but lip seals typically last only about 2,000 operating hours—three months (Chapter 8, Ref. 1). When lip seals are too tight, they tend to cause shaft wear (Fig. 8.1, top portion) and, in some instances, lubricant discoloration (“black oil”, Chapter 8, Ref. 2) and contamination. Once lip seals have worn and no longer seal tightly, oil is lost through leakage. The API-610 standard for process pumps disallows lip seals and calls for either rotating labyrinth-style or contacting face seals.

Pump Wisdom Chapter 8: BEARING HOUSING PROTECTION AND COST JUSTIFICATION

Fig. 8.1: Lip seals (left and top right) tend to wear and have typically only a 3-month operating life; replacement with a high-reliability rotating labyrinth seal (below, right) is possible without first having to repair damaged shaft surface

The bearing housing protector seal in the lower right portion of Fig. 8.1 incorporates a small and a large diameter dynamic O-ring. This bearing protector seal is highly stable and not likely to wobble on the shaft; it is also field-repairable. With sufficient shaft rotational speed, one of the rotating (“dynamic”) O-rings is flung outward and away from the larger O-ring. The larger cross-section O-ring is then free to move axially and a micro-gap opens (Chapter 8, Ref. 2).

1. Brink, R. V., Czernik, D. E. and Horve, L. A.; “Handbook of Fluid Sealing,“(1993), McGraw-Hill, New York,
ISBN 10: 0070078270.

2. Bloch, Heinz P. and A. Budris; “Pump User’s Handbook: Life Extension,” 3rd Edition (2006), Fairmont
Publishing Company, Lilburn, Georgia, ISBN 0-88173-629-9.

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