05.03 How do I determine the required flow rate and pressure?

Here are some quick rules of thumb for determining flow rates and pressures. More precise calculations are often warranted by the requirements of the application, but this is a start.

Flow Rate for Boilers: Take the consumption of all of the boilers at full load. Then multiply by 2 to get the desired flow rate. This will make sure that the pump is fully capable, and helps assure that the last boiler in a series will not be starved for flow.

Pressure at Pump for Boilers: Take the required pressure at the boiler inlet. Add 25% for safety factor. Add 10 PSI for flow loss in piping (and size the piping for a max 10 PSI loss). Add the vertical head from pump to boilers and the suction head from tank to pump. The sum of these will be a good estimate for the required pressure at the pump.

Notes for Boilers: Some boilers and heaters require very low pressure inlets and the challenge to to provide that low pressure. Pressure regulators at the boilers is often a solution, as are head tanks with a continual overflow back to the bulk storage tank.

Flow Rate for Generators: Take the consumption of all generators at full load. Then multiply by 2 to get the desired flow rate. This will make sure that the pump is fully capable, and helps assure that the last generator in a series will not be starved for flow. If the potential for starving day tanks further along in the series is apparent, then flow regulating valves should be used at the day tank inlets to be precise. Also do not oversize the inlet valves.