Difference between GD¦ vaue and Moment of inertia of pump

[nirlt]

Please explain the difference between GD² vaue and Moment of inertia of pump.

Whts the improtance of both the values in selection of motor for pump??

 

[BigInch]

GD^2? What are you trying to do and what's the rest of the formula?

Wet Moment of Inertia of pump + motor is used for determination of angular acceleration during starts, stops and speed changes.

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[PersonalProfile]

Are you referring to GD^2 and Mr^2 where the difference is 2^2 = 4?
That is you are talking about the same measurement, less two different systems of measurement?

Regards,
Lyle

 

[cbrn]

Hi,
GD^2, or PD^2 as it can be also found, is the "old" way of expressing the polar inertia of a shaftline. As Lylebrown says, it is 4 times the value of the inertia. "GD^2" is however mostly used in hydraulic turbomachinery.
As it has been already said, the rotary inertia of the shaftline influences the transient operations (startup, shutdown, load rejection, runaway); the bigger the inertia, the slower the shaftline can vary its speed in response to transient conditions. For example, if you have a mandatory specification on the max overspeed during load rejection, increasing the inertia is one way to keep under the specification. Ah, well, I'm speaking of a turbine, but the same concepts apply to pumps of course.

Regards