So what is a sump pump, you ask? A sump pump is usually an electric pump that is placed in the basement of a home, and used to pump water from the basement to outside the home. Sometimes sump pumps drain the water into the house’s drainage pipe system, and sometimes they simply pump the water outside.

Sump pumps normally work in combination with a sump pit. The sump pit is simply a hole dug into the ground, generally in the basement of a house, which allows water to collect into it. The pump then pumps the water out of that sump pit hole.

A basement sump pump is most often used in cases where the house’s basement is below the water table level, and in places where flooding is common. Sometimes these pumps are also used if the bottom level of a house is below sewer lines.

Sump pumps can be useful, particularly as a precaution, in almost any area though, for all homes which have basements. When rain comes and the soil around your home’s foundation gets wet, that water can leak into the basement. And even just an inch or so of water on the basement floor can do extensive damage that’s quite expensive as well. Particularly if you have a finished basement with furniture in it.

These days, the most common pump for a shallow well is a jet pump. Jet pumps are mounted above the well, either in the home or in a well house, and draw the water up from the well through suction (see Single-Drop Jet-Pump System diagram on next page). Because suction is involved, atmospheric pressure is what’s really doing the work. Think of the system as a long straw. As you suck on the straw, you create a vacuum in the straw above the water. Once the vacuum is there, the weight of the air, or atmospheric pressure, pushes the water up the straw. Consequently, the height that you can lift the water with a shallow-well jet pump relates to the weight of the air. While air pressure varies with elevation, it’s common to limit the depth of a jet-pump-operated shallow well to about 25 ft.

Jet pumps create suction in a rather novel way. The pump is powered by an electric motor that drives an impeller, or centrifugal pump. The impeller moves water, called drive water, from the well through a narrow orifice, or jet, mounted in the housing in front of the impeller. This constriction at the jet causes the speed of the moving water to increase, much like the nozzle on a garden hose. As the water leaves the jet, a partial vacuum is created that sucks additional water from the well. Directly behind the jet is a Venturi tube that increases in diameter. Its function is to slow down the water and increase the pressure. The pumped water–new water that’s drawn from the well by the suction at the jet–then combines with the drive water to discharge into the plumbing system at high pressure.

Because shallow-well jet pumps use water to draw water, they generally need to be primed–filled with water–before they’ll work. To keep water in the pump and plumbing system from flowing back down into the well, a 1-way check valve is installed in the feed line to the pump.