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N°7 – Single and double pumps training – A level

Double pumps have a common casing and two impellers, driven by two motors. Pumps with one impeller are called single pumps.
Double pumps allow:

  • A fall-back option if there is a problem with one of the motor or impeller,
  • To obtain if necessary more flow(*) for simultaneous operating of the 2 impellers. In this case we say that the pumps are operating in parallel.

(*) Increasing the flow rate will only occur if the hydraulic resistance of the network is not excessive (see course : Theory of pumps in closed circuits – level 2 ).

  • Each pump can be operated alternately:

Each pump acts as a replacement for the other, which ensures operating security with no risk of the system stopping.
The programming of the pump switching is done at the control panel.

  • Both pumps can operate simultaneously:

For a given required flow a programmed parallel operation of the 2 pumps can lead to substantial savings both at the purchase and the operating stage.
The maximal hydraulic performance is provided by the parallel operation of the 2 pumps, but just one operating pump can supply approx. 85% of the performance required for the installation.

For maximum security it is possible to install 2 single pumps in parallel as you can see in the following video.
It is always necessary to equip each single pump with a non-return valve if we want to switch automatically from one pump to the other.


Watch the video below and then answer the questions.


Indicate below the position of the valves to allow the pumps to operate in parallel or in series.