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.