Some systems have a particularly high head requirement compared to the flow, or a particularly high flow requirement compared to the head. In these situations it can be more difficult to find a suitable pump that will operate efficiently and fulfil the system requirements. One solution is to use two, smaller pumps. This doesn’t double the flow and the head, however…
There are two ways to connect two pumps together, in ‘series’ or in ‘parallel’. ‘Series’ is when the discharge of the first pump is connected to the suction of the second pump. ‘Parallel’ is when the incoming flow is connected to both suctions, and the discharges are both connected to the outgoing flow. Like light bulbs, they will perform differently depending on how they are connected.
Series pump configuration
The pressure, or ‘head’, is doubled when two pumps of the same type are connected in series. The flow stays the same.
Parallel pump configuration
The volume, or ‘flow’, is doubled when two pumps of the same type are connected in parallel. The head stays the same.
A multistage pump is like connecting pumps together in series, so the pressure increases for every impeller you add.
The above image shows a booster set with six vertical multistage pumps connected in parallel. Each pump, with multiple impellers connected in series, produces good pressure, and the set will generate that fixed pressure however many pumps are running. By then connecting the pumps in parallel the flow can be increased to meet demand by turning more pumps on.
An additional complication in this example is the variable speed drives mounted on top of the motors. The variable speed drive will reduce the frequency that the motor runs at, which in turn reduces the flow in direct proportion (so half speed motor = half flow), and the pressure in proportion to the square of the motor speed (so half speed motor = quarter pressure). The booster set can now adapt to meet an infinitely variable requirement (within upper and lower limits) while operating efficiently.
Contact us to discuss your requirements!