Pump rotation to provide pressure or volume flow

[robax25]

how much rotation needs to start volume flow for a adjustable variable pump?.I get it 5pi from the book. Is there any rule that it needs such rotation to start volume flow. From where I get it?I think that pump designer does not give the information on the manual.

 

[russ_watters]

I am a mechanical engineer and have never heard of any of that. Do you have a source with more information on it?