Sump and Sewage Pump Flow Rate & Minimum Run Time

Norm Hall
May 31, 2010
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The last few articles focused on the sump diameter and float levels. The flow rate is also used in the sump sizing. Obviously, the pump flow rate must be greater than, or equal to, the maximum expected effluent flow into the sump. In addition, the sump storage from the lead pump on, float to the off float, must be large enough so we do not cycle the pumps too often.

Let’s look at an example: Assume you are designing a storm water sump pump system and you have determined you need to pump 50 GPM against 20 feet of head. You select a B&G 2DES series effluent pump with a ½ HP motor, since you only expect ¾” solids and want the advantage of dual seals, with moisture sensing, between the two seals. Your head selection is based on 3” pipe size, which is just above the minimum velocity of 2 FPS (see MMM of 4-26-10). You could have also chosen 2” pipe with a 4.5 FPS velocity.

You want pump guide rails, and based on the MMM article from 5-17-10, you select the recommended 60” diameter sump for 3” pipe. Today’s article advises you have 500 gallons of storage between pump on and off. Based on the chart above, you will require about 42” of storage level.

Next week we will examine the float levels for the lag pump and alarm conditions.

Disclaimer: R. L. Deppmann and it’s affiliates can not be held liable for issues caused by use of the information on this page. While the information comes from many years of experience and can be a valuable tool, it may not take into account special circumstances in your system and we therefore can not take responsibility for actions that result from this information. Please feel free to contact us if you do have any questions.

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