How efficient should the pump be?

We often talk about the optimum efficiency that a pump should have, in this article we explain what the efficiency of a pump is and how it is calculated.

By efficiency we mean the nominal flow rate, the manometric head and the absorbed power that the pump must have in order to optimise the installation.

The nominal flow rate is the volume of liquid required in a given time. It is usually expressed in litres/minute or m3/hour.

The manometric head of the installation is the total head of the liquid. The sum of the suction head (Ha) plus the delivery head (Hi) is called the geometric head (Hg). The latter added to the pressure drop is the gauge head (Hm).

These are the head losses of the liquid due to friction with the pipe. These losses increase with the roughness, length of the pipe and the flow rate through it. And they are reduced if the pipe diameter increases. Obstacles such as reductions, extensions, valves or elbows (singular losses) also contribute to increase the head losses.
It is established that the head losses due to 90º bends are equivalent to 5 linear metres of pipe and those due to valves to 10 metres.
According to the above, it is recommended not to exceed a head loss of 4%. In particular, in order to favour the work of the pump, it is recommended to install pipes of a larger diameter on the suction side.

Equivalent length of straight pipe (in metres).
Approximate values, variable depending on the quality of the fittings (valves, elbows, etc.).

Diagram to determine pressure drop and fluid velocity as a function of flow rate and pipe bore.

Effective for calculations and pump selection that do not require a very high degree of accuracy.

In smooth PVC/PF pipes