What this tool does
Convert a target minimum pump run time into required drawdown, then estimate the idealized nominal precharged-tank volume at the entered settings.
When to use it
Use for preliminary conventional on/off pump systems. Select the actual tank from manufacturer drawdown tables at the exact pressure switch settings.
Inputs and supported units
Each labelled field explains the quantity it expects. Unit-system changes convert existing numeric entries once and keep calculations on a single SI internal basis. Supported shared units include L/min and GPM, metres and feet, kPa and psi, millimetres and inches, kW and hp, and °C and °F as relevant.
Calculation or decision method
Gauge pressures are converted to absolute by adding atmospheric pressure. The tool requires precharge < cut-in < cut-out.
How to interpret the result
Read the primary result with the supporting breakdown and warning. A plausible number is not evidence that every input, operating case or design constraint has been included.
Worked example
A 40 L/min pump with a 1-minute target needs 40 L drawdown. At 193 kPa precharge and 207/345 kPa cut-in/out, the idealized fraction is about 29.5%, requiring roughly 136 L nominal volume.
Assumptions
Ideal-gas behavior, fixed atmospheric pressure and a conventional captive-air tank without thermal or bladder-volume corrections.
Limitations
The idealized result does not replace rated manufacturer drawdown, code rules, motor start limits or variable-speed system guidance.