Neither can I based on the very small snippet of data you've given us.

where does frequency come into it?

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I've just considered it might be frequency.Given data provides that; head at 55 HZ.

I am asking that anybody knows like this formula;

Head* (1,1)^2 = max head

Ok.

I think you're looking at affinity law here relating to the speed of a centrifugal pump.

This law states that the head varies as a square of the speed. Therefore for a pump with a head h1 at 50 htz, all other things being the same, the head at 55 htz is h1 x (55/50)^2 or h1 x (1.1)^2.

Flow is proportional to speed and power proportional to speed^3.

Just search "affinity law pumps".

You use it to calculate the change in head when you change speed, e.g. on when using a VFD.

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Also: If you get a response it's polite to respond to it.

Thank you very much LittleInch...