Field calculator
Tank fill and drain time calculator
Knowing how long a tank, basin, or pool takes to fill or empty drives the pump sizing, the schedule, and the operator's plan, and the basic relationship is simple: time equals volume divided by flow rate. Enter the volume in gallons and the flow in gallons per minute to get the minutes and hours. The estimate assumes a steady flow, which holds well for a pump running at a fixed rate, but two real-world effects make a gravity system slower than the constant-rate figure. A gravity drain loses head as the level drops, so it runs fast at first and slows toward the end, taking longer than a single average rate suggests. And a pump does not hold one flow either; it moves along its performance curve as the head changes, so the delivered flow at the real operating point is what counts, not the nameplate maximum. For sizing a fill cycle or a pump-down, use the actual delivered flow and add margin for the slowdown. Confirm the pump selection, the drain sizing, and any code-required fill or drain time with the manufacturer and the engineer.
Result
Tank fill or drain time: time = volume divided by flow rate. Enter the volume in gallons and the flow in gallons per minute to get the minutes and hours to fill or empty a tank, basin, or pool. The result assumes a steady flow, which is a good estimate for a pump running at a fixed rate, but two real-world effects make a gravity system slower than the constant-rate number: a gravity drain loses head as the level drops, so it slows toward the end, and a pump moves along its curve as the head changes. For sizing a fill or a pump-down, use the actual delivered flow at the operating point rather than the nameplate, and add margin. Confirm the pump selection, the drain sizing, and any required fill or drain time with the manufacturer and the engineer.
anvilfield.com/calculators/tank-fill-drain-time-calculator · Free field calculators and FieldOS. A planning estimate, verify against the code, the manufacturer, and the engineer of record.
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Fill/drain time FAQ
How does a well pressure tank work?
A well pressure tank stores water under pressure on a cushion of trapped air, usually behind a rubber bladder, so the pump does not run every time you open a tap. As you draw water, the compressed air pushes it out at pressure. The pump refills the tank only when pressure falls to the cut-in setting.
What is the difference between a submersible and a jet pump?
A submersible pump sits down in the well below the water and pushes it up, handling deep drilled wells efficiently. A jet pump sits above ground and pulls water by suction, capped near 25 ft for a shallow single-pipe model or deeper with a two-pipe ejector. Submersible suits deep wells, jet suits shallow.
Why does my well pump short cycle?
Short cycling, the pump snapping on and off every few seconds, is usually a waterlogged pressure tank that has lost its air charge, so it holds no drawdown. A bad pressure switch or a clogged sensing port can also do it. Find the cause fast, because short cycling burns out a pump quickly.
What pressure should a well tank be set at?
Set the pressure switch for the building, commonly 30/50 or 40/60 psi, where the pump starts at the lower number and stops at the higher. Then set the tank air pre-charge about 2 psi below the cut-in, with the tank empty, so 28 psi for a 30/50 switch or 38 for a 40/60.
How deep can a jet pump pull water?
A shallow-well jet pump pulls water by suction and is capped near 25 ft of lift at sea level by atmospheric pressure, less at altitude. A deep-well two-pipe jet with an ejector reaches roughly 90 ft. Past that, the well needs a submersible pump set down below the water.