Well Pump Cycle Rate Calculator
ANA›Life Services Authority›National Calculator Authority›Well Pump Cycle Rate Calculator
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Well Pump Cycle Rate Calculator
Calculate how many times per hour your well pump cycles on and off, and determine if your pressure tank is properly sized to protect your pump from short-cycling damage.
Pressure Tank Total Volume (gallons)
Total rated volume of the pressure tank (not drawdown volume)
Pump Flow Rate (GPM)
Gallons per minute your pump delivers
System Demand Flow Rate (GPM)
Average household demand in gallons per minute
Cut-In Pressure (PSI)
Pressure at which pump turns ON
Cut-Out Pressure (PSI)
Pressure at which pump turns OFF
Tank Pre-Charge Pressure (PSI)
Air pre-charge pressure (typically 2 PSI below cut-in)
Calculate
function welCalc() { var tankVol = parseFloat(document.getElementById('wel-tank-volume').value); var pumpFlow = parseFloat(document.getElementById('wel-pump-flow').value); var demand = parseFloat(document.getElementById('wel-demand-flow').value); var cutIn = parseFloat(document.getElementById('wel-cut-in').value); var cutOut = parseFloat(document.getElementById('wel-cut-out').value); var precharge = parseFloat(document.getElementById('wel-precharge').value); var resultDiv = document.getElementById('wel-result');
// --- Validation --- if (isNaN(tankVol) || isNaN(pumpFlow) || isNaN(demand) || isNaN(cutIn) || isNaN(cutOut) || isNaN(precharge)) { resultDiv.style.display = 'block'; resultDiv.className = 'calc-result calc-error'; resultDiv.innerHTML = 'Error: Please fill in all fields.'; return; } if (tankVol = cutIn) { resultDiv.style.display = 'block'; resultDiv.className = 'calc-result calc-error'; resultDiv.innerHTML = 'Error: Pre-charge pressure must be less than cut-in pressure.'; return; } if (precharge = pumpFlow) { resultDiv.style.display = 'block'; resultDiv.className = 'calc-result calc-error'; resultDiv.innerHTML = 'Error: Demand flow must be less than pump flow rate for the pump to keep up and cycle properly.'; return; }
// --- Drawdown Volume Calculation --- // Using Boyle's Law: V_drawdown = V_tank * (P_cutout - P_cutin) / (P_cutout + 14.7) * (P_precharge + 14.7) / (P_cutin + 14.7) // Accurate drawdown formula for bladder/diaphragm tanks: // V_drawdown = V_tank * [ (P_precharge + 14.7) / (P_cutin + 14.7) - (P_precharge + 14.7) / (P_cutout + 14.7) ] var Pa = 14.696; // atmospheric pressure (PSI absolute) var P_pre_a = precharge + Pa; var P_in_a = cutIn + Pa; var P_out_a = cutOut + Pa;
var drawdown = tankVol * P_pre_a * (1 / P_in_a - 1 / P_out_a);
if (drawdown ' + 'Status' + '' + status + '' + 'Drawdown Volume' + '' + drawdown.toFixed(2) + ' gallons' + 'Pump ON Time per Cycle' + '' + (t_on * 60).toFixed(1) + ' seconds' + 'Pump OFF Time per Cycle' + '' + (t_off * 60).toFixed(1) + ' seconds' + 'Cycle Time' + '' + (t_cycle * 60).toFixed(1) + ' seconds (' + t_cycle.toFixed(2) + ' min)' + 'Cycles per Hour (at current demand)' + '' + cyclesPerHour.toFixed(1) + ' cycles/hr' + 'Max Possible Cycles/Hour (worst-case demand)' + '' + maxCyclesPerHour.toFixed(1) + ' cycles/hr' + 'Recommended Max Cycles/Hour' + '' + recMax + ' cycles/hr' + 'Minimum Required Drawdown' + '' + minDrawdown.toFixed(2) + ' gallons' + 'Minimum Tank Volume Needed' + '' + minTankVol.toFixed(1) + ' gallons (total rated volume)' + '' + '' + advice + '
'; }
#### Formulas Used
Drawdown Volume (Boyle's Law for bladder/diaphragm tanks):
Vdrawdown = Vtank × (Pprecharge + 14.696) × [1/(Pcut-in + 14.696) − 1/(Pcut-out + 14.696)]
All pressures converted to absolute PSI (gauge + 14.696).
Pump ON Time per Cycle:
Ton = Vdrawdown / (Qpump − Qdemand) (minutes)
Pump OFF Time per Cycle:
Toff = Vdrawdown / Qdemand (minutes)
Cycle Rate:
Cycles/Hour = 60 / (Ton + Toff)
Minimum Required Drawdown:
Vdrawdown,min = Qpump × 60 / (4 × Maxcycles/hr)
Derived from the worst-case condition where demand = Qpump/2, which maximizes cycle rate.
#### Assumptions & References
- Assumes a bladder or diaphragm pressure tank (not a galvanized air-over-water tank).
- Boyle's Law (P&sub1;V&sub1; = P&sub2;V&sub2;) governs air volume changes in the tank at constant temperature.
- Atmospheric pressure is taken as 14.696 PSI for absolute pressure conversion.
- Industry standard maximum cycle rate is 6 cycles per hour for most residential submersible and jet pumps (Goulds, Grundfos, and Pentair pump guidelines).
- Pre-charge pressure should be set to 2 PSI below cut-in pressure per pressure tank manufacturer recommendations (Amtrol, Well-X-Trol).
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