Machine Design
In replacing the V-belts, a complete set of new belts is used instead of replacing a single damaged belt because

Only one belt cannot be fitted with other used belts
The new belt will carry more than its share and result in short life
Belts are available in sets
New and old belts will cause vibrations

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Machine Design
In hydrodynamic bearings

Grease is used for lubrication
The oil film pressure is generated only by the rotation of the journal
Do not require external supply of lubricant
The oil film is maintained by supplying oil under pressure

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