Manufacturers are required to provide a sump pump performance curve for each sump pump model. The performance curve tells the consumer how many gallons of water can be pumped from the pit at a specified height during a specified time period. Buying a new sump pump by this measurement is more accurate than buying by pump horse power because some 1/2 HP pumps can move as much water as 3/4 HP. It is important that you know how much water enters and leaves your pit during a heavy rainstorm and what the vertical height is of the discharge pipe system. Using these measurements will enable you to find the size pump you need. If you are confused and need more detail, try these instructions on how to use a sump pump performance curve.
A sump pump performance curve is a charted diagram that shows how much water a sump pump can pump at a specified vertical height.
Pump manufacturers are required to provide such documentation for each sump pump model so that purchasers can buy the right sized pump for their water pumping needs. Installing a sump pump with insufficient pumping performance leads to basin overflow and a flooded basement because the sump pump was not built to sufficiently handle the volume of water flowing into the basin in one minute. Some manufacturers choose to chart pumping performance per hour.
Reading a sump pump curve involves understanding the two axis charted: the vertical height, also known as total dynamic head height, and the gallons per minute or per hour.
The vertical height to which the water will be pumped from the basin before it is removed to it destination is measured in feet and many times in liters as well. The most common measurements are zero, five, ten and fifteen feet. Sometimes this measurement is also found in meters. This height can be measured at the place of sump pump installation by putting a tape measure in the basin bottom and locating the highest vertical height to which the water will be pumping from the basin.
The second axis measures the amount of water that can be removed from the basin per minute or per hour. That measurement is commonly defined as gallons per minute and sometimes liters. Gallons per minute can be converted to gallons per hour by multiplying GPM by 60 (number of minutes in one hour).
So to apply the performance curve to a specific pump installation it is necessary to know the vertical height and then identify where the gallons per minute and vertical height axis intersect. To make it easier, manufacturers show a pre-drawn curve for each vertical height measurement the pump is capable of pumping.
Here's more detailsd instructions for measuring the size sump pump needed for your water pumping needs.
To most accurately determine which size sump pump is needed, it is important to measure the vertical height water must be pumped from the pit.
When the next heavy rains storm occurs note how many times the sump pump cycles on and off per minute. On an average of four to seven gallons of water is pumped per on off cycle for an eighteen inch diameter pit. If the pump cycles 5 times, every 12 seconds, in one minute then approximately 20 to 35 gallons would be pumped every minute and 1,200 to 2,100 gallons per hour. At this pumping rate most one-third horse power pumps would be sufficient.
But it is important to check the manufacturers pump performance chart to confirm. One-half horse power pumps typically pump 35 gallons to 60 gallons per minute.
Installing a sump pump with too much horse power causes the pump to turn on and off too quickly and causes motor short cycling which prematurely wears the motor out.
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