In series operation, what must be equal between the pumps?

In series operation, the key characteristic that must be equal between the pumps is the pump heads. When pumps are configured in series, they are designed to increase the overall pressure of the fluid being moved, and the total head produced by the system is the sum of the heads of each individual pump. Hence, while the capacities of the pumps can vary, they should be selected based on their ability to operate effectively at the required head.

In practical terms, if the pumps were to have significantly different heads, it could lead to inefficient operation, potential damage, or even failure due to one pump working harder than necessary while the other may not contribute effectively to the system. Therefore, ensuring that the pump heads are properly matched for series operation is crucial for maintaining system efficiency and reliability.