How do pump manufacturers determine the design rate of flow and total head for each pump on the chart?

The quick answer is they do the best they can, but there is a method generally accepted in the industry

  • The horizontal spacing between pumps is determined by a reasonable flow velocity for the discharge opening of the pumps.
    • The popular pipe sizes, 1”, 11вЃ„2”, 2”, 3”, 4”, 6”, etc. also double in area in progression. Hence, pumps increase in rate of flow in a doubling progression (factor of 2).
  • Total head between adjacent pumps typically increases by a factor of 1.6.
    • This allows an appropriate coverage range for each pump without an excessive reduction in efficiency at the lower end of the pump’s coverage.
  • These factors of 2 (for rate of flow) and 1.6 (for head) also result in diagonally spaced pumps having the same design specific speed (NS).
    • As an example, a 3” discharge pump with a 10” impeller has the same NS as a 4” discharge pump with a 13” impeller, and is, therefore, geometrically similar.