How Sump Pumps Work

By Brian Simkins

There are quite a few things in your house that you bought simply because you wanted them - your plasma T.V., your computer, maybe even a deep freeze or a commercial oven. Chances are, you did the research, and then you made a purchase that changed the quality of your daily life. In addition to these premeditated purchases that enhance your home are vital implements that keep your house functioning the way that it should. One of these key pieces that you probably don't spend a lot of time thinking about is your sump pump.

The sump pump is what removes waste water from underneath your house. It usually sits in a pit that is built into your basement floor or crawlspace. The concrete floor is poured slightly downhill when the house is built so that any liquid will flow right into that pit. The sump pump, through a series of pipes, ejects the waste water out of the house into various places, which we will discuss briefly.

The sump pump sits in the bottom of the pit and has a switch that is activated by the water level. When you have water in your basement, it flows into the pit, the pump is activated and it pumps the water out of the pit and into your septic field or right into the city sewer. In some instances it may just pump right out into your yard, but this doesn't meet local building ordinances in many locations.

Types of Sump Pumps and How They Work

One of the most common types of sump pumps is a pedestal pump. A motor is mounted on a small pedestal. The entire unit usually stands about 30" tall. A hose or a pipe extends down from the motor to the bottom of the pit. On a separate metal rod there is a float. As the water level in the pit raises and lowers, this float moves up and down. This is called a float switch. When the float reaches a certain height (because the water level pushed it there), it activates the motor and the water is sucked up through the hose and ejected through another pipe. The motor on this pump is not designed to be underwater. The switch will always activate before the water level comes up to the bottom of the pump.

Another type of sump pump is a submersible pump. It is a much smaller unit, usually about 12" tall, that sits in the bottom of your sump pit. Some pumps that fall within this style have a float switch on a rod just like the pedestal pump, but the rod is only about 4 inches tall. Others have a different type of float switch. The electrical switch itself is encased in a hard plastic bubble. As the water level rises, the bubble floats. When it floats so high that it reaches a vertical position above the pump, the switch is activated and the pump kicks on.

Unlike the pedestal pump, the submersible pumps don't have an intake pipe that sucks up the water that is to be sent out. Instead, the pump is located right at the bottom of the unit. The water is actually sucked right up through the bottom of the pump. There are several benefits to this type of action. First, if there is any loose gravel or debris in your sump pit (and there usually is), the submersible pump comes with a screen or a grate over the face of the pump that will prevent the debris from being sucked up into the impeller of the pump. The impeller is what creates the suction, and if it gets damaged, it's going to be time to buy a new pump. Unfortunately, this is what kills a lot of the pedestal style pumps - the hose or pipe that reaches down into the bottom of the pit sucks up any and everything.

If you do have an application where you need to be able to eject some small debris, then there are pumps that will do that. If you have a crawlspace that is not concrete, but just pea gravel, for example, you may need an ejector pump that can handle small debris. These are a little bit pricier, but are usually constructed of cast iron and have a 2" ejector port instead of the standard 1 1/4" port that you will find on most sump pumps. This increased size and a different style of impeller allows these pumps to process small pieces of gravel and debris without damaging the mechanism.

In rare instances, there are still applications for sewage pumps. You really shouldn't ever need one in a new house because it is illegal to handle your sewage this way almost everywhere, but in some older homes it may still be an issue. This happens when all of the waste water in the house is funneled into the sump pit. All of your dishwater, shower water, washing machine drainage and yes, maybe even the toilet would be directed to flow right into the bottom of the sump pit. If this is the case, then you need a sewage pump that will deal with whatever solids may be flowing in. You can use your imagination and then come to the conclusion that you want a pump that will get this stuff out of your house.

Take the time to shop around. Whether you are buying for the first time or are replacing a unit that isn't functioning properly, you can find some great deals. I would always recommend buying a unit with cast iron housing as opposed to plastic. If the plastic were to crack for some reason, then you would have open electrical components sitting in a pit of water - not good. Also compare warranties. Most of the major manufactures offer a full replacement lifetime warranty on their better units. Make sure you register your purchase so that you can capitalize on this warranty should you ever need to.