please, make an effort to ask this question in a better way so that could be better interpreted

Dear Mr Giuseppe Starace,

Kindly refer to the image attached. In calculation of the NPSHa, is the gauge pressure inside the tank and the vapor pressure of the fluid being cancelled off? And the NPSHa equals to Hz - Hf?

sorry but in the picture there's no reference either to Hz or to Hf or to the difference.

I see that the pump is under the level of the tank and you won't have any problem of NPSHa ... except in very rare cases.

Problems arise when the pump is over the tank level.