Pumps can be arranged in serial or parallel to provide an additional head or flow rate capacity.
Centrifugal pumps in series are used to overcome larger system head loss than one pump can handle alone.
With a constant flowrate the combined head moves from 1 to 2.
Note! In practice the combined head and flow rate moves along the system curve to point 3.
Series operation of single stage pumps is seldom encountered - more often multistage centrifugal pumps are used.
Centrifugal pumps in parallel are used to overcome larger volume flows than one pump can handle alone.
Note! In practice the combined head and volume flow moves along the system curve as indicated from 1 to 3.
In practice, if one of the pumps in parallel or series stops, the operation point moves along the system resistance curve from point 3 to point 1 - the head and flow rate are decreased.