As I vary the flow rate and the head, I get curves which are called

characteristic curves, which are shown here.

Imagine I have a valve on here and I open and close the valve and

therefore vary the flow rate and the head.

That as they vary, I get graphs which look like this.

So this is for example, the flow rate Q and

this curve here is the head hp.

And in particular if I completely close the valve so that there's

no flow rate through here, I still have a head, I'm still increasing the pressure.

And the head at zero flow rate is called the shut off head.

Similarly, the power w., is given by

this expression here and if I compute the ratio of those two,

the power to the delivered to the water to the pumping power.

I get the efficiency eta, which has a curve which looks something like this.

And at some point here we have a maximum in the efficiency

which is obviously the point where we have designed the pump to operate.

Where that occurs is called sometimes the BEP.

The best efficiency point and it occurs at the normal or the design flow rate.

So, these curves for a pump are called the characteristic curves of the pump,

and here is the corresponding section from the reference manual.

That covers the basic ideas and equations of pumps and

turbines, and in the next segment we'll look at some examples.