Sump Pump Failure—Your Discharge Pipe May Be Too Small


Sump Pump Failure—Your Discharge Pipe May Be Too Small

The sump pump has often been described as the “heart” of a basement waterproofing system and this is a pretty accurate description.  After all, a sump pump moves water through a drain tile system and out of the house, similar to the function of that most important of human organs.

The sump pump, again like the heart, depends on clear, unobstructed pathways for its flow.  If drain tile, for example, is installed improperly and becomes obstructed, water can’t get to the sump pump for removal.

A more frequent occurrence, though, is an obstruction on the discharge side of the sump pump, which can take the form of a stuck check valve but most often results from a flaw in installation – an improperly sized discharge pipe.

How the Wrong Discharge Pipe Can Cause Sump Pump Failure

There are many things to look for when choosing a sump pump – construction, horsepower, type of float switch – but the most important factor is pumping capacity.

Every sump pump is rated for a certain pumping capacity, usually rated in gallons per minute, which is a fairly easy way to compare pumps.  After all, a sump pump that moves 61 gallons per minute has to be better than one that moves 34, right?

Well, yes, but there are two other factors to consider that, if not heeded, can lead to sump pump failure.

If the consumer looks closely at the capacity ratings for sumps pumps, he or she will see that the rating is based on a certain “head height,” usually 10 feet.  This refers to the vertical distance that the pump has to push water until it reaches the point where it exits the basement.  In a typical eight foot high basement, the head height is 10 feet, accounting for the depth of the sump basin.

If the head height is smaller, the pump will move a little more water per minute; if it is larger, the capacity will diminish.

More importantly, the capacity rating of the sump pump is also based on using the right-sized discharge pipe.  Most sump pumps have a built-in fitting for a certain sized discharge pipe, typically 1.25” or 1.5” inside diameter.  (Because most sump pump discharge pipe is PVC, determining interior diameter is important.  These pipes will be closer to 1.5” and 2” on the outside respectively.)

Using a properly sized pipe for discharge will ensure that the sump pump will perform as the manufacturer intended.  Installing discharge pipe of a larger size is not a huge problem and is in fact recommended for longer runs of pipe, typically 20 feet or more.

The real problems occur when the diameter of the discharge pipe is too small.  When the discharge pipe is smaller than recommended, the pump’s capacity and efficiency are reduced.  The pump cannot push its rated volume of water through the small pipe and the increased friction creates back-pressure that makes it even more difficult to move the water.

The result is that the sump pump will run much more frequently because each discharge cycle will take longer than it is supposed to due to the reduced volume of water; the pump will kick on more frequently because the basin has more time to fill while the pump is laboring to empty it.  In periods of heavy and/or frequent rain, this can result in the pump running constantly for hours at a time.

Of course, all that running and stress on the motor will cause it to burn out quicker, cutting short the life of the sump pump and necessitating a replacement.

The best way to ensure that a sump pump is sized and plumbed properly to protect a specific home from water is to have it installed by a basement waterproofing professional.  At U.S. Waterproofing, we’ve installed thousands of sump pumps, both primary and back-up, for the more than 300,000 customers we’ve served since 1957.  We supply only top quality pumps and have highly trained installers that understand the importance of taking into account head height and size of the discharge on every sump pump they install.  Why not ask for our free advice?


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