In order to extend the overall performance of the pump within the system, multiple pumps are typically connected in series or in parallel.
Pump connected in parallel
The use of pumps in parallel is usually the case where the required flow is greater than the flow that can be provided by a single pump and the flow requirements of the system are variable, and these requirements are met by switching the parallel pumps.
Typically, pumps in parallel have the same type and size. However, sometimes the pumps can vary in size, or one or more pumps can be speed controlled and therefore have different performance curves.
In order to avoid bypass loops in pumps that are not operating, each pump is installed with a check valve in parallel. The overall performance curve of a system consisting of multiple pumps in parallel is determined by summing the flows of the pump at a given head.
Since the pumps are identical, each pump curve has the same maximum lift, but the overall maximum flow becomes twice that of a single pump. The flow rate corresponding to each head is double the flow rate of a single pump.
Variable speed pump in parallel
When the flow demand changes, in order to obtain efficient pump performance, it is very effective to combine the pump in parallel with the variable speed pump. This method is commonly used in water supply/boost systems.
A pumping system consisting of two variable speed pumps with the same performance curve has a wide performance range.
Even though a single pump can maintain the required flow and head, it is sometimes necessary to use both pumps simultaneously for efficiency and energy consumption. Whether to choose a single pump or two pumps depends on the specific system characteristics and pump type.
Pump connected in series
Typically, pumps are connected in series in systems that require high pressure. In addition, this is also the case for multistage pumps based on the principle of series (ie one stage equivalent to one pump). The overall performance curve is obtained by plotting twice the head of each flow value in the coordinate system. This allows the curve to have twice the maximum head and the same maximum flow as a single pump.
Different pumps can be pumps of different sizes or a combination of one or more variable speed pumps. In systems where a constant high pressure is required, a combination of a fixed speed pump and a variable speed pump is typically employed. The constant speed pump supplies fluid to the variable speed pump, while the output of the variable speed pump is controlled by a pressure transmitter.