Pressure drop inside pumps seal

[Azraelo]

Hi!
Could you help me, please?
I'm reading a manual about pressure drops along a pump seal. I understand that the mechanical seals have two parts: stationary seal and rotationary seal. Between them there is a gap, and the gap is filled with the pumped fluid. But I don't understand very well why the pressure drops linearly when the rotational seal starts to rotate and why it becomes some kind of "cuadratic" distribuition when the seal is rotating. I understand that the gap is just a few microns wide, so perhaps the fluid mechanics has a special formulas for these situation. I'm taking these information from page 15 of the Grundfos Pumps Manual. Please your kind help.

Link

Thanks!

--
Az

 

[BigInch]

It becomes noticably quadradic when frictional pressure due to the velocity squared term becomes more prominent.

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