Geometry & drainage
Fill / drain time at constant flow
- where
- fill / drain time (min)
- volume to transfer (L)
- volume flow (L/min)
Explain this equation
Works out how long a volume will take to fill or empty at a steady flow. Use it for cylinders, tanks and system fills or drain-downs.
V is the volume to transfer. q is the flow rate.
Time is volume divided by flow rate. Both are in litres, so the litres cancel and the answer comes out in minutes.
Sense check: 150 L at 12 L/min takes 12.5 minutes. Double the flow and the time halves.
Watch out: this assumes constant flow. Gravity drainage slows as the level drops, so real times are often longer. No simultaneous inflow or outflow is allowed for.
Enter your values to see the result.
Good to know
Assumes constant flow and no simultaneous inflow/outflow. Gravity drainage is rarely constant.
Sources
Results are arithmetic only. Worked examples are not recommended design settings. This library does not provide automatic gas pipe selection, live gas tightness tests, purging procedures, combustion acceptance limits, installation approval or commissioning certification. Manufacturer data and the applicable current method remain essential.