How a Sump Pump Works

A sump pump works by pumping water in sump pit up and out of a home to the land outside the home.

Water gets into the pit by perforated pipes, often called a french drain, that are installed in the soil around the foundation of the home. As rain or snow melt percolates down through the soil it eventually runs into these pipes. These pipes then carry the water to the sump pit. Older homes may not have these pipes and in that case water percolates through the soil and runs into the pit directly.

Once the water is in the sump pit it will accumulate there until the water level rises high enough to switch on the sump pump via a float switch. When the float rises with the water level the switch eventually engages and turns on the pump. The pump then forces the water out of the pit through a pipe to the land outside the home.

If the pump discharges the water to a drain line inside the home that goes to the municipal sewer system, or a septic tank, that is a problem. This is because the sewer processing plant is designed to process sewage, not ground water. If every home with a sump pump pumped the water to the sewer it would overload the sewage treatment plant and if it’s not overload it will increase the costs of processing sewage a lot! The water that enters the sump pit is ground water and should be discharged to land around the home that hopefully is sloped away from the home so that the water runs away from the home instead of toward it so that it does not affect the foundation.

One detail about installing a sump pump that is very important is when the pump is activated. You want the pump to be activated before the water level reaches the bottom of the pipes that drain water into the pit. Otherwise water will be collecting around your foundation which is what the sump pit and pump are designed to eliminate.

Another detail about purchasing a sump pump is the type of switch that is used. There are two types that I have seen. One is what I call a ‘swing type’ and is a bulb on the end of a wire, it looks like a tube, that will swing up and down as the water goes up and down. The advantage of this type is that it will turn the pump on less frequently because the of the long wire that the bulb is connected to. The disadvantage of this type is that as the bulb floats up and down it can easily be caught on wires, pipes or debris that is in the pit and then fail to turn the pump on or turn it off. Both of which are bad bad bad. The other thing is that you have to adjust it so that the pump comes on before the water level reaches the bottom of the pipes draining water into the pit. In a shallow pit this can be a problem.

The other type of switch also uses a bulb but its travel is more restricted to a vertical motion instead of a swing motion by using a rigid lever instead  of the wire. This type of switch will cause the pump to run more often because the shorter ‘swing’ of the lever arm but it is much less likely to get caught on something and works better in a pit where the pipes draining into the pit are close to the bottom of the pit.

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