Learning how to size a sump-pump is very important. If the horsepower is too small it will not keep up with the water entering the pit and the basin will overflow. If it is too large, the-basin water will be removed too quickly and the motor will short cycle shortening its life.
Basement sump pump sizing is affected by the following factors: 1) Height of the-basin 2) Diameter of the-basin 3) Vertical height of discharge pipe from pump port to horizontal pipe leaving the house 4) Number of elbows and check valves in discharge pipe system 5) Rate of water-flow into the-basin during heavy rains.
The following steps take the above mentioned factors and create a sump pump sizing calculator. Following these seven steps will help you to choose the best sump-pump horse power and pumping performance needed.
Take a yardstick and rest one end on the bottom of the pit. Check the number of inches to the top which is at the basement floor level. This is the height of the-basin.
Take a yardstick and lay it across the top of the pit. The distance from one wall to the other is the diameter of the basin. The most common diameter is 18 inches. Some are 24 inches. A 24 inch diameter is wonderful because two submersible sump pumps fit easily on the bottom. If a battery backup is attached in-line with the discharge-pipe or a water powered sump-pump is used, three pumps will easily fit.
Take a sturdy tape measure. Stick it into the pit resting one end on the-basin bottom. Measure straight up until the highest point of the discharge pipe is reached. Do not be concerned about the bends or slopes at this point.
Look for the number of connectors inserted into the discharge pipe as it is angled to go to the outside of the house. Record the degree angle of each connector. Count the number of check valves inserted into discharge pipe. Every system should have at least one check valve. A check valve prevents the motor from re cycling the same water over and over because when the motor stops some water remains in the discharge-pipe and because of gravity will flow back into the pit which could be enough to cause the motor to run again. This will cause short cycling and a shortened motor life. If more than one check valve, one ninety degree elbow and one 45 degree elbow are used, enough friction could be caused to one-half foot to the vertical discharge-height.
Check the sump-pump manual to identify the pump motor ON point and OFF point. For example, let's say the manual says ON is 7 inches and OFF is 3 inches. This means the motor runs after 4 inches of water enters the pit and during heavy rains keeps running every time four inches of water enters the-basin.
Use your watch digital reading or a time piece second hand to see how frequently the motor runs in one minute during heavy rainstorms. For example, let's say the motor runs every 10 seconds.
Now take the above measurements and put them all together to calculate the water flow rate and pumping performance required. We are using a discharge-pipe diameter of 1-1/2 inches (1.5-in.). A smaller diameter cannot handle the same volume. Likewise a larger diameter can handle more volume.
The actual calculation is as follows.
At a minimum, manufacturers provide the following information.
Use the documentation provided by the manufacture if you want to find the right size sump pump for your pumping needs.
Manufacturers specifications, pumping performance curve and manuals for over one hundred sump pumps can be found at Sump Pumps Online Express.
Learning How To Size Sump Pump is easy if you do the steps prescribed above. The key steps are: Make sure you know the measurements of your sump-basin, the vertical height of the discharge-pipe, and the distance between the float-switch ON and OFF point. Take those measurements to calculate the water flow rate into the sump-pump-basin. Check the manufacturing documentation to find the right size pump. Installing the right size sump-pump is very important to preventing both flooding and motor burn out.
Manufacturer's documentation is readily available at Sump Pumps Online Express. Before you buy your next sump-pump, make sure you have the right size.
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