Explain pumps operating in series versus parallel configurations.

Series operation: pumps connected sequentially, flow remains constant while heads add. Used when single pump cannot provide required head (e.g., multistage pumps, booster applications). Combined curve shows same flow with doubled head. Parallel operation: pumps share common suction and discharge headers, heads equalize while flows add. Used to increase flow capacity or provide redundancy. Combined curve shows doubled flow at same head. Parallel operation requires matching pump characteristics; pumps with significantly different curves may cause one pump to operate inefficiently or even run out (low flow, high temperature). VFDs help balance parallel pump operation.