20353779 Centrifugal Pumps Bearings Part 2

8/6/2019 20353779 Centrifugal Pumps Bearings Part 2

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Centrifugal Pumps Bearings

Bearing Assembly DesignShaft and Housing Fits:

As a general rule, a rolling element bearing should be

installed so that its inner race is a tight fit on the rotating

shaft and the outer race is an interference fit in the

stationary housing. The tolerances for shafts and bearing

housings should be established using the recommendations

of bearing manufacturers or ISO standards.


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Bearing Assembly DesignThermal Expansion:

Shaft


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Bearing Assembly DesignThermal Expansion:

Shaft

Held BearingFree Bearing


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Bearing Assembly DesignTypes of Mounting:

Shaft Nut and Locking Washer:

This is one of the most common

arrangements and can be usedfor both single and double row

radial bearings. After tightening

the nut, the tab washer is bent

against one of the flats on the

nut, so preventing it turning.


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Slotted Nut and Pin:

A castle nut or slotted nut may

be used with a split pin or cotterpin in order to provide

adjustment for tapered roller

bearings .


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End Plate and Locking Screws:

This arrangement may be used

as an alternative to the slottednut and pin.

Each screw has a small hole

drilled through the head, through

which a wire is passed and its

ends twisted together. The wirethus prevents the screws from

becoming loose.


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End Cap and Shims:

This arrangement may be used

for tapered roller bearings or forangular contact bearings where

pre-load has to be set with

adjusting shims.


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Snapring:

When it is not suitable for the

housing to contain a shoulder,then a snapring can be used to

locate the bearing in the housing .

This requires a special bearing

with a recess machined in the

outer race to enable the snapringto be fitted.


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Adaptor Sleeve:

Some types of bearing are made

with a tapered bore and aremounted as "floating" bearings on

an adaptor sleeve .

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Typical Pump Bearing Arrangements:Ball Radial and Ball Thrust:

For shaft diameters up to about

55 mm and speeds up to 3600

rpm, anti-friction double-rowangular-contact bearings may

be used for both radial loads

and thrust loads in either

direction.


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Typical Pump Bearing Arrangements:Ball Radial and Ball Thrust:

Because of the rolling action of

the balls between the races,

the heat generated is not asgreat as a plain bearing. Most

of the heat which is produced is

due to the sliding action of the

balls against their retaining

cage which maintains equal

ball spacing.


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Typical Pump Bearing Arrangements:Ball Radial and Ball Thrust:Lubrication is usually provided

by an oil ring which hangs from

the shaft with its lower partdipped into an oil reservoir in

the bearing housing. As the

shaft rotates, the oil ring

splashes oil to the bearings.


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Typical Pump Bearing Arrangements:Sleeve Radial and Ball Thrust:

For shaft diameters and

speeds which are above the

limits for ball radial and ballthrust construction, cylindrical

sleeve bearings are used to

carry the radial loads.

Axial loads in either direction

are taken by two ball bearings

mounted back-to-back.


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Typical Pump Bearing Arrangements:Sleeve Radial and Ball Thrust:

The sleeve bearings are steel

or bronze lined with Babbitt and

are split parallel to the shaft.Lubrication may be by oil rings

and cooling coils may be built

in to the oil reservoirs through

which either cold water or the

pumped product may be

circulated to remove excessheat from the oil. mounted

back-to-back.


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Bearing Lubrication:The choice of lubricant is determined by the following

factors:

Load - The load on the bearing will determine the pressure against

which the lubricant must work.

Speed - The lubricated surfaces will wear faster at higher speeds.

Temperature - The properties of the lubricant may be affected by

the operating temperature.

Environment - The lubricant may have to cope with the presence

of water or corrosive substances.


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Bearing Lubrication:Lubricantselection should normally be in accordance with

the recommendations of the equipment manufacturer.

However, as a general rule, the following guide is useful to

remember:For light loads and high speeds, use a lubricant of low viscosity.

For heavy loads and low speeds, use a lubricant of high viscosity.


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Bearing Lubrication:The decision whether to use oil or grease as the lubricant

will depend upon operating conditions. The following

comparative advantages may be useful to consider when

making a choice:Oil:

Assists cooling.

Absorbs less torque.

Feeds more easily and form a central supply.

Washes away dirt.

Can also lubricate other elements such as gears.


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Bearing Lubrication:

Grease:

Permits simpler bearing designs.

Provides better sealing against foreign matter.

Is easier to contain and seal.

Allows longer periods without attention.


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Bearing Lubrication:The following basic principles govern the application of

lubricants:

Cleanliness is vital. Lubricating equipment must be kept free from

dirt and other foreign matter.

Lubricants of different brand or grade should never be mixed.

If it is necessary to change the type of lubricant, then the

equipment should first be drained and cleaned out.

An excess of lubricant, especially grease, will cause heat tobuild up. This will eventually break down the lubricant and bearing

failure will result.


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Lubricant filters and strainers should always be changed at the

recommended time intervals.

The selection of lubricant for a given application should be as

recommended by the equipment manufacturer.

Inadequate lubrication can often be identified by the operating

condition of the bearing, such as excessive noise or temperature.In general, if a bearing feels too hot to touch with a hand, then its

lubrication may not be correct and should be checked.


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Lubricants are potentially hazardous materials and should be

properly stored with regard to safely and effect on the environment.


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Bearing Lubrication:Oil:

Oil lubrication is often used for light to moderate duty in

high-speed applications.

The oil should be changed at regular specified intervals

and this should be done sooner if the oil has become dirty

or contaminated.

When changing oil, it is good practice to thoroughly cleanthe bearing housing or sump with flushing oil before

adding the new lubricant. This ensures that all foreign

matter is removed.


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Bearing Lubrication:Grease :

Grease lubrication is generally used for heavy loads at low

to moderate speeds.

When grease is used in pump bearings, make sure it is ofthe type specified by the pump manufacturer.

Usually, soda-soap-compounded grease that has a

mineral oil base is acceptable.

All greases used for bearings should be free from fillers

such as clay, mica or talc. These mineral fillers are highly

abrasive, even when finely ground and mixed with oil or

grease.


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Bearing Lubrication:Grease :

Pumps are greased at around 3 monthly intervals and this

may be extended to 6 months if the pump is not operated

frequently.When the pump is running, however, the bearings should

be checked daily for noise, cleanliness and operating

temperature.


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Bearing Lubrication:Methods of Lubrication:

Lubrication methods include:Oil reservoirs.

Constant-level oilers.

Drip-feed.

Ring type oilers .

Pressurized systems.

Whatever method is used, daily checks should be made to

ensure that the correct amount of lubricant reaches the

bearings.


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The constant-level oiler is a combination drip feed and ring

type oiler.

The ring used to distribute the oil is the same as any otherring oiler.

Its purpose is to maintain a constant oil level in the sump

by replacing the oil that leaks out.


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Some pumps are fitted with grease cups . Lubrication is

carried out by turning the cap or handle one or two turns at

regular intervals.


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Bearing Seals:There are two main types of bearing seals:

Contacting type seals (rubbing).

Clearance type seals (no rubbing).


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Bearing Seals:

A

D

G

F


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Bearing Seals:

B

The simplest type of clearance seal is obtained

by providing a relatively long close-clearance fit

between the shaft and housing. One or more

grooves may be arranged in the housing to

help prevent the escape lubricant.

Slingers are often fitted to clearance seals

when they are used for oil-lubricated bearings.

The slingers help to prevent the escape of any

oil which may have passed the seal by flingingit into a groove in the seal housing, from where

it can drain back into the bearing housing .


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Bearing Seals:

B

Another type of clearance seal is the

labyrinth type . In a labyrinth seal, the long

and staggered close-clearance path is filled

with lubricant and offers a high resistance

to flow in either direction.

Clearance type seals can operate without

any restrictions regarding speed or

operating temperature, but they do permit

more leakage of lubricant than rubbingcontact seals and also are not as effective

in keeping out dirt and other foreign matter.

20353779 Centrifugal Pumps Bearings Part 2

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Transcript of 20353779 Centrifugal Pumps Bearings Part 2