Operational risks of operating centrifugal pumps in series 1

[Lan85]

I have been working on a hydraulic calculation for a client to check whether pumps provided by a vendor can do the intended job.
I need 34m head to transfer the water and each of the vendor pump (vendor provided two) have a head of 22m at the required flowrate.
I thought arranging pumps in series will be a solution, however our lead engineer has said that operating pumps in series can be problematic and not recommended.

What are some operational problems of operating centrifugal pumps in series? Anyone have practical experience on this?

Thanks

 

[Rinchterninsob]

Trim the impeller on the upstream pump to achieve the correct net discharge head. Both pumps do NOT have to be the same trim (think about an OH pump feeding a BB3). Install a bypass line with check valves. Then start the upstream pump first to allow it to pack the line before starting the downstream pump (this way there is no concern of dropping suction pressure too quickly causing cavitation, as would potentially be the case if there was no downstream pressure).

Now, you have room to grow later in the upstream pump should you need it, and the capability of running at variable heads/flowrates, should you need to.