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Lift Station Calculator - Pump Cycles, Backup Power & Overflow Risk

Size generators and calculate time to overflow for any lift station

Calculate pump cycles per day, lead pump runtime, backup generator sizing, and time to overflow for any wastewater lift station. Enter daily flow, wet well volume, and pump capacity to see pump cycling frequency, runtime hours, and emergency backup requirements. Includes generator kW sizing, fuel consumption estimates, and a prominent overflow countdown showing how long before sewage reaches the surface during a power outage.

Pro Tip: The single most important number for any lift station is time to overflow with no power. If that number is less than 2 hours, your emergency response plan needs to assume you will have a spill. Most small-town lift stations have 30-90 minutes before overflow during average flow conditions. During a rain event, that shrinks to minutes.

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Lift Station Runtime & Backup Power Calculator
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How It Works

  1. Enter Station Configuration

    Input average daily flow (GPD), wet well active volume (gallons between lead-on and lead-off levels), pump flow rate (GPM), and number of pumps.

  2. Enter Pump and Motor Data

    Input pump HP for generator sizing calculations. The calculator estimates starting current, running load, and total power demand.

  3. Configure Backup Power

    Enter generator tank size or let the calculator recommend a generator kW rating based on pump motor sizes and building loads.

  4. Check Overflow Risk

    See the prominent time-to-overflow display for both average and peak flow conditions. Red warnings appear when time is less than 2 hours.

Built For

  • Collection system operators evaluating overflow risk during power outages
  • Public works directors sizing portable or permanent generators
  • Engineers designing new lift stations with adequate wet well volume
  • Emergency planners estimating response time requirements
  • Operators tracking pump cycles for maintenance scheduling

Frequently Asked Questions

Time to overflow = (Wet well volume above current level) / Inflow rate. For average flow: convert GPD to gallons per minute (GPD / 1440). If your wet well has 500 gallons of capacity and inflow is 35 GPM, time to overflow = 500/35 = 14.3 minutes. That is the time from lead pump failure to sewage at grade level.
Add up the running kW of all equipment that must operate simultaneously, then add the starting surge of the largest motor. Pump starting current is typically 6 times running current. A 10 HP pump needs about 8.5 kW running and 51 kW starting. Size the generator for starting load plus running load of all other equipment, with a 25% safety factor.
Most lift station pumps should cycle 4-10 times per hour maximum. Excessive cycling (more than 10/hr) causes motor overheating, control wear, and higher maintenance costs. The minimum wet well volume to prevent excessive cycling depends on pump flow rate: larger pumps need larger wet wells to keep cycle frequency reasonable.
Disclaimer: This calculator provides estimates for planning purposes. Actual overflow risk depends on I/I conditions, wet well geometry, alarm response time, and weather. Generator sizing should be verified by a licensed electrician. Always maintain emergency response plans and portable pumping capability regardless of backup power availability.

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