Water and wastewater · Worked step by step
What is the detention time for 60,000 gallons at 500 GPM?
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The problem
A tank holds 60,000 gallons and the flow through it is 500 gallons per minute. What is the detention time in minutes?
Grab a pen and paper first
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Watch it solved, with you
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Press play and I’ll write it out with you, one small step at a time.
Every step gets a plain-words explanation here, so you always know exactly what just happened and why.
The written version, step by step
- 1
Write what you know
volume = 60,000 gal • flow = 500 GPM
- The tank holds 60,000 gallons.
- 500 gallons flow through each minute.
- Per minute, so the answer is in minutes.
- 2
Divide volume by flow
time = 60,000 ÷ 500 • time = 120 minutes
- Volume divided by flow: 60,000 ÷ 500.
- 60,000 ÷ 500 = 120.
- So the detention time is 120 minutes, which is 2 hours.
Quick trick: Cancel two zeros from each: 600 ÷ 5 = 120.
Remember this for good
Detention time = volume divided by flow. Gallons over GPM gives minutes.
Volume on top, flow on the bottom, and the flow was per minute, so the answer is minutes.
Solve it fast next time
- Detention time = volume divided by flow.
- Gallons over GPM gives minutes.
- 120 minutes is also 2 hours.
The answer: 120 minutes.