Critical Speed in pumps

Critical Speed is the speed at which the dynamic forces caused by rotation make a shaft to rotate in its natural frequency.  The vibrations produced as a result can cause serious damage to the equipment.  Hence, rotating equipment should be operated above or below the critical speed to avoid the risk of damage.

Pumps, being rotating equipments, also have a critical speed.  The speed is dependent on factors such as the stiffness, length and mass.  The details of the critical speed for each pump will be provided by the manufacturer.

The operating speed of the pump is mentioned in the nameplate details.  Low speed pumps will have a operating speeds below the critical speeds such as 1440 rpm.  High speed pumps, on the other hand, will have their operating speeds above their critical speeds.

When these pumps are started, they will have to cross the critical speed  to reach the operating speeds.  Operators will gradually ramp the speed of these pumps to a value below the critical speeds and then rapidly cross the critical speed range to reach the operating speed.