# N°1 – Presentation of centrifugal hydraulic pumps training – NVQ to A level

Centrifugal hydraulic pump’s role is to circulate water in a system.

Inside the pump casing an impeller (n°1) is turned at high speed by an electric motor (n°2).

We recognise that with:

• Pumps in closed circuits (heating and air-conditioning systems, domestic water circuits etc.) the water is continuously recycled.
• Pumps in open circuits (sump or cellar pumps, draw pumps, filling pumps, booster pumps, etc…) the water is not or only partly recycled.

For fluids to circulate it is necessary to create pressure differences, with the fluid always circulating from “high” pressure point to “low” pressure point.

In a horizontal tube, water can only flow from a point A to a point B if the pressure at point A is higher than that at point B.
This pressure difference, or head loss (Δp) corresponds to the friction of the water on the sides of the pipe.

The pressure difference necessary for the circulation can be supplied by a pump. This is called the Tdh of the pump: Total dynamic head.

The difference in pressure between A and B is generated by the pump
This difference is called the Total dynamic head (Tdh) of the pum

• In closed circuits the difference in pressure to be supplied is not very high. It corresponds to the friction of the water in the pipes and in the installation (head losses).
Head losses and pump Tdh can be studied in the course “Calculation of head losses and the Tdh of closed circuit pumps”.
• In open circuits the pressure difference to be supplied by the pump is often very high. It corresponds to:

– The height (H) by which the pump has to raise the water
– The friction in the pipes and installation (head losses)
– The residual pressure (pr) necessary at the evacuation.

The Tdh of pumps in open circuits can be studied in the E-book : “Operating characteristics of pumps in open circuits “.
Pumps in open circuits can be studied in the E-book : “Technology of pumps in open circuits -part 1” and in the E-book: “Technology of pumps in open circuits -part 2”.

The centrifugal pumps shown in this section are generally used in closed circuits. They supply small and medium pressure differences of between 1 [mH2O] and a few dozen [mH2O].