Pumps can be arranged in serial or parallel to provide additional head or flow rate capacity.
[h=Pumps in Serial - Heads Added]3[/h]
When two (or more) pumps are arranged in serial, their resulting pump performance curve is obtained by adding their heads at same flow rate as indicated in the figure below.
Centrifugal pump in series are used to overcome larger system head loss than one pump can handle alone. For two identical pumps in serie the head will be twice the head of a single pump at the same flow rate. With constant flowrate the combined head moves from 1 to 2. In practice the combined head and flow rated moved along the system curve to 3.
If one of the pumps stops, the operation point moves allong the system resistance curve from point 1 to point 2 - head and flow rate are decreased.
Series operation of single stage pumps is seldom encountered - more often multistage centrifugal pumps are used.
[h=Pumps in Parallel - Flow Rate Added]3[/h]
When two or more pumps are arranged in parallel their resulting performance curve is obtained by adding their flowrates at the same head as indicated in the figure below.
Centrifugal pumps in parallel are used to overcome larger volume flows than one pump can handle alone. For two identical pumps in parallel the flowrate will double (moving from 1 to 2) compared to a single pump if head is kept constant. In practice the combined head and volume flow moves along the system curve as indicated from 1 to 3.
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.