Bearing Housing Seal Upgrades Can Improve Pump Reliability - Water World

8/6/2019 Bearing Housing Seal Upgrades Can Improve Pump Reliability - Water World

1/3

Hello Log In | RegisterAdvanced Search

0 Share

Print Email Save

Bearing Housing Seal Upgrades Can Improve Pump Reliability

By Allan R. Budris

As pointed out in prior columns, the second leading cause of pump break downs is bearing failures. This is because

fewer than 10% of all ball bearings run long enough to succumb to normal fatigue failure (20,000 hours for an ANSIPump). Most bearings fail at an early age because of static overload, wear, corrosion, lubricant failure, contamination, or

overheating.

Particle contamination and corrosion related failures account for 52% of all of these bearing failures. Bearing housing

seals, and more specifically the seal type, play a crucial role in this centrifugal pump reliability component. They serve to

both retain the lubricant within the bearing housing and to exclude both solid and liquid contaminants that can find

openings to infiltrate both the lubricant and the bearings.

To further complicate this is sue, bearing housings breath in and out as they cool down and heat up with shut down and

start up. If a path or opening exists (through a housing vent or bearing housing shaft seal) to the external environment,

ambient air will be induced to flow into the housing. Figure 2 shows just how s ensitive bearing reliability is to even sm all

amounts of water. This is of m ost concern in humid environments.

Traditional Bearing Housing Seals

Many pumps today are still equipped with large open vents and short-lived, wear-prone lip seals. These traditional

bearing housing seals are generally inadequate. When these seals are in good condition, they contact the shaft and

contribute to friction drag and temperature rise in the bearing area. Then they wear out after as little as 2,000 to 4,000

operating hours. This wear (and any open vents) creates paths for the bearing housing to breath in contaminants.

Bearing Isolators / Labyrinth Seals

Improved protection can be provided with non-contacting labyrinth seals (sometimes called bearing isolators). Rotating

labyrinth seals represent a commendable advancement over prior art. They have proven to give much better protection

than either lip seals or standard stationary labyrinth seals .

However, the standard bearing isolator still has a fixed air gap that permits comm unication between bearing housing

space and ambient environment. Non-contacting rotating labyrinth configurations cannot, therefore, provide a fully effective

barrier against the intrusion of atmospheric dust or moisture.

Some bearing isolators have attempted to close up this air gap (at least during shut down) by use of O-rings that are

intended to lift off slightly on running pumps. They are intended to reseal the bearing housing after the pump is stopped.

However, even this device cannot be considered a totally effective housing seal for oil-lubricated pump bearings, since it

is unable to fully prevent the interchange of vapors inside the bearing housing. If the O-rings lift off after restarting, ambientair at higher pressure gets into the bearing housing. If the rings do not lift off, then there is no gap between the rotors O-

rings and the opposing s tator surface. In this case, the rotating O-rings could undergo wear and again not perform as a

nothing in / nothing out hermetic seal.

Rotating labyrinth seals seem to work best when the housing vent is plugged.

Advertisement

Subscribe: Newsletter Magazine

Home Community Drinking Water Wastewater Urban Stormwater Industrial Water Water Utility Mgmt Environmental World Regions Buyers Guide

North Am erican and Carribean Latin America Europe Middle East Africa India/Central Asia Far East/SE Asia Australia/Oceania

23/05/2011 Bearing Housing Seal Upgrades Can I

waterworld.com//bearing-housing-s 1/3


2/3

Magnetic Bearing Housing Seals

So what is a reliability focused pump user to do? Fortunately the aircraft and aerospace industries have brought us

magnetic face seals, which are compact enough to replace lip s eals, and provide a true hermetic seal for bearing

housings. Research performed at Texas A&M University concluded that a magnetic seal leaks less than any other type of

seal and operates with a low coefficient of friction, torque, electric power consumption and heat generation, and is an

affordable way of sealing ball bearing housings.

In pumps equipped w ith magnetic bearing housing seals , the lubricant is totally contained while the atmosphere is

effectively excluded. The shaft is sealed with magnetic seals at each end of the frame. In general, the rotary portion of the

seal i s fastened to the shaft by an O-ring that performs both clamping and s ealing functions. The opposing component is

O-ring mounted in a stationary fitting, which is then fitted into the pump housing or frame adapter. Instead of springs to

hold the faces together, one of the components of a modern dual-face magnetic bearing housing seal is fitted with a

series of sm all rare earth rod magnets.

Dual-face magnetic seals are the preferred configuration. The application options for dual-face magnetic bearing housing

seals are almos t limitless . They are presently used on m any pump configurations, including horizontal and vertical

pumps. Their dimens ional envelope fits many locations where lip s eals were originally installed. The external faces of the

modern dual-face magnetic seals were originally designed for dry running and will do so without distress as long as the

respective internal faces are kept cool, with marginal oil s plash lubrication on the inner face of this seal.

To insure full hermetic sealing of the bearing housing, these m agnetic shaft seals mus t be coupled with a diaphragm-

type expansion chamber and balanced oilers (is used).

Limitations

To safeguard against blatant misapplication, the manufacturers of magnetic seals warn against dry running. As a matter

of general policy, either continuous monitoring or other appropriate inspection and examination methods are advocated to

ensure correct equipment oil levels. Fortunately, the bearing housings of properly designed pumps will always

incorporate lube application methods that generate an oil fog that results in not only adequate bearing lubrication but also

a thin coating of oil for the seal faces. Only the complete loss of oil could cause an unacceptable temperature increase at

the inboard / outboard faces. Then again, thats an academic concern since deprivation of lube oil would invite

catastrophic bearing failure in any case.

For bearing housings in pure oil mist s ervice, dual-face magnetic seals are provided with features that promote oil mis t to

coalesce on the seal faces. In that case, pre-lubrication of the faces will be required since, upon starting the equipment,

oil mi st will not instantly coalesce in sufficient amounts to form a s eparating film between seal faces. Properly applied

and installed, modern dual-face magnetic seals have always won in laboratory tests (and case histories) against every

other bearing housing seal. As a result, double-face magnetic bearing housing seals often show dramatic life cycle cost

savings due to the reduction of operating and maintenance costs.

Conclusions

Reliability focused pump users can improve the life cycle costs of their pump ins tallations by upgrading the bearing

housing s haft seals to avoid premature bearing failures from oil contamination. And finally, it should be noted that, in most

cases, even the simplest oil lubrication design will outlast grease lubricated pumps, es pecially those with s ealed for life

bearings, since the oil lubricated bearings will typically run cooler with s uperior lubrication.

WW

Reference: Pump Users Handbook, Life Extension, third Edition by Heinz P. Bloch & Allan R. Budris, Third edition, 2010,

by Fairmont Press, Inc.

About the Author: Allan R. Budris, P.E., is an independent consulting engineer who specializes in

training, failure analysis, troubleshooting, reliability, efficiency audits and litigation support on pumps

and pumping systems. With offices in Washington, NJ, he can be contacted via e-mail at

[email protected].




3/3

More WaterWorld Current Iss ue Articles

More WaterWorld Archives Iss ue Articles

People who read this article also read the following:Motor Control Modernization Improves Pump Performance

California water utility retrofits facility with corrosion-resistant screw pumps

Flood Damage Prompts City to Install Pressure Sewer System

Innovative water technologies recognized in annual competition

Report lists America's most endangered waterways

Latest ArticlesMaryland passes lawn fertilizer bill to help reduce polluted stormwater runoff(May 20, 2011)

Four water, wastewater systems in NC, VA bought by Aqua America (May 20, 2011)

Water, energy projects in western states get WaterSMART grants(May 20, 2011)

Bay-Delta w ater e fficiency projects get funding from federal agencies(May 19, 2011)

WaterWorld Weekly: May 19, 2011 (May 19, 2011)

CAFO to pay record fine for Clean Water Act violations(May 19, 2011)

Water utility reduces disinfection by-products with MIEX system (May 19, 2011)

Water infrastructure monitoring to improve water supply in Antofagasta, Chile(May 19, 2011)

Major engineering firms to combine(May 19, 2011)

Chesapeake Energy fined record penalty for contaminating private water supplies(May 18, 2011)

Water WorldArticle Categories:

Drinking Water Environmental

Wastewater World Regions

Stormwater / Urban Water Products & ServicesWater Utility Managem ent Current Issue

Subscribe | Contact Us | Industry Links | Advertising |

PennWell | Privacy Policy | Terms & Conditions | About Us | Site Map | RSS | Webmaster

PennWell Websites | PennWell Events

Copyright 2011: PennWell Corporation



Bearing Housing Seal Upgrades Can Improve Pump Reliability - Water World

Documents

Transcript of Bearing Housing Seal Upgrades Can Improve Pump Reliability - Water World