Centrifugal Pump Power

It depends upon the characteristic curves for each pump and the characteristic curve of the system. Each pump will operate where each curve intersects with the system characteristic curve.

Without sight of these three things, it is not possible to provide a more detailed answer.

However, <...at 7 M3/hr and 25m head...> an <...0.4kW...centrifugal pump...> is already overloaded by at least +20%.

The hydraulic power here is 0.39kW, so the pump requires more than 0.4kW. A pump of that size is likely to have efficiency ~ 60% on water, and could be lower depending on the fluid viscosity.

Your question doesn't make much sense. The pump absorbed power is determined by its curve and the system curve, and the motor must be sized for that.

Will you be changing the impeller size to match the additional power? But the way,... pump curves are used to determined the power requirement based on you pumping needs.

Keep in mind, and PWSlack brought up,... pump curves are based on water at 60º-70º F.

I suggest you contact your pump supplier. And keep in mind, if your supplier doesn’t have the ‘hands on experience’ and rely only on paper responses, such as Pump manufacturer pump curves, your supplier will refer you to the manufacturer.

and good luck with that.

Become familiar with pump performance curves and understand what they mean.....

The wording of your question implies that you either have no idea what you are doing or simply couldn't be bothered presenting all information