Adding head and flow for pumps arranged in parallel vs. serial.
Pumps can be arranged and connected in series or parallel to provide additional head or flow capacity.
Pumps in series – head added
When two (or more) pumps are arranged in series, the pump performance curve bomba result is obtained by adding your heads at the same flow rate indicated in the figure below.
Centrifugal series pumps are used to overcome system head loss greater than one pump can handle alone.
- for two identical pumps in series, the head will be twice the head of a single pump with the same flow – as indicated in point 2.
At a constant flow rate, the combined head moves from 1 to 2 – BUT , in practice, the combined head and flow move along the system curve until point 3.
- point 3 is where the system operates with both bombs working
- point 1 is where the system operates with a bomb working
Note that for two pumps with equal performance curves operating in series
- the head for each pump is equal to half of the handle at point 3
- the flow to each pump is equal to the flow at point 3
The operation of single-stage pumps in series is rarely encountered – more often multi-stage centrifugal pumps are used.
Parallel Pumps – Added Flow Rate
When two or more pumps are arranged in parallel, their resulting performance curve is obtained by sum of pump flows at the same manometric height, as indicated in the figure below.
Parallel centrifugal pumps are used to overcome larger volume flows than one pump can handle alone.
- for two identical pumps in parallel and the head kept constant – the flow doubles compared to a single pump as indicated in point 2
Observation! In practice, the combined head and volume flow move along the system curve as indicated by 1 to 3.
- point 3 is where the system operates with both bombs working
- point 1 is where the system operates with a bomb working
In practice, if one of the pumps in parallel or in series stops, the operating point moves along the system resistance curve from point 3 to point 1 – the head and flow decrease.
Note that for two pumps with equal performance curves running in parallel
- the head of each pump is equal to the head at point 3
- the flow to each pump is equal to half the flow at point 3
Note – for parallel operation
- Zero flow or “shut off valve” heads must match the pumps
- unstable pump bends should be avoided
- steeper pump curves are preferred
Source: https://www.engineeringtoolbox.com/pumps-parallel-serial-d_636.html
