Bugs wrote:
The power curve for centrigugal pumps peaks at maximum flow & pressure.
At zero flow [blocked outlet] very little power is used because the
only work being done is slightly heating the fluid. At maximum flow and
zero head there is also very little work being done because there is no
lift [pressure increase].
Only positive displacement [cylinder or gear] pumps have a problem with
low flow.

Not universally true.

Some centrifugal pumps do require a minimum flow for
cooling parts of the pumphead - like bearings. In one
actual centrifugal pump rated for 45 l/min, that I just
had for repair, the minimum flow is 3 l/min and this
pump has plastic sleeve bearings inside pumphead.

It all depends on the pump design.

Kristian Ukkonen.