When operating pumps in parallel or in a series, there are more complex issues to consider.
Series applications: consider the pressure rating of pump, shaft seal, pipework and fittings. Placement is critical to ensure both pumps are operating within their recommended range and will have a constant supply of water. Drawing a curve for 2 or more pumps is simple, draw 1st pump curve then draw 2nd curve, adding the head each pump produces at the same flow. More curves can be added in the same way.
Parallel applications: confirm suitability of pumps by drawing a system curve (often 2 pumps will only deliver slightly more than one pump due to excessive friction loss. Also you can confirm that pump operation will be within its recommended range.). Non return valves are required especially if one pump operates alone at times.Dissimilar pumps or pumps placed at different heights requires special investigation. Drawing a curve for 2 or more pumps is simple, draw 1st pump curve then draw 2nd curve, adding the flows each pump delivers at the same head. More curves can be added in the same way.
