Calculating Flow Into a Lift Station

Have you ever been working on a broken pump at a lift station and wondered how fast the water is entering the lift station or how much time you have before it begins to overflow? Well, I know some operators would say, “I hate math so much that by the time I finished the math to figure it out, I would be standing in the water.” Although math can sometimes seem challenging, the more you practice it and the more problems you work, the more you can tie it into the routines and job duties that you perform every day. Eventually, you will be able to see its place in our industry.

Let’s take a look at the lift station below. In this practice scenario, let’s assume that the facility is having a very bad day and both pumps at the lift station have failed. The lift station is 50 feet deep with a diameter of 23 feet. The influent flow causes the water level to rise 18 feet, 9 inches in 3 hours and 42 minutes. What is the influent flow rate in gallons per minute?

The first step is to find the volume of water in the cylinder. To do this, convert inches to feet.

Lastly, convert the volume of water to gallons:

Now that you have determined the volume of water in the lift pump, you want to calculate the number of minutes the pump ran to create that volume of water. To do this, convert hours to minutes. (Remember, there are 60 minutes in an hour.)

Now you can calculate the flow rate.

Knowing the dimensions of your lift station is helpful. This is a quick way to see how fast the water is coming in.

Now you can determine when your lift station will overflow. First, find the remaining volume of the lift station. The water height is already at 18 feet, 9 inches. So the new height is 50 feet – 18 feet, 9 inches = 31 feet, 3 inches.

Convert this volume to gallons:

Now calculate the time you have before the lift station overflows:

Lastly, convert this decimal into actual minutes:

So now you know how long you have before it overflows if there is no pumping. Good luck on staying above water.

Check out the Test Your Knowledge – Calculating Flow Into a Lift Station post for additional practice problems.

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