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What does a sump pump do?

by Manage My Life Last activity date:
April 26th, 2007

What does a sump pump do?

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Sump pumps are designed to handle rain and melting snow that accumulate around the building. They don't handle solids. Sump pumps are usually provided when there is a risk of flooding subgrade areas. Exterior perimeter drainage tile may drain into a sump pump system. Gutters and downspouts may also discharge into a sump pump system, although this arrangement is risky because it brings outdoor storm water into the building. Downspouts are best arranged to discharge above grade several feet from the house.

Some houses need sump pumps because the general slope of the land is such that surface rain and melting snow accumulate around and under the foundations. In other areas, sump pumps are necessary because the water table is particularly high, at least during some parts of the year. The municipality may require a sump pump if the storm sewers are higher than the lowest floor level.

The presence of a sump pump is a yellow flag. Look carefully for dampness in subgrade areas and possible chronic flooding problems.

A sump pump system consists of a sump (tank) that is typically buried below basement floor level. It has a side inlet, sometimes several of them. The sump may be made of concrete, plastic or metal. In some cases, the sump is merely a hole dug out of the subgrade earth. These kind of sumps usually collapse over time.

The pump is in the sump. The pump may be a

pedestal-type

with the electric motor mounted above the sump. The pump may also be a

submersible-type

with the motor and pump at the bottom of the sump. In either case, there will be 120- volt electrical power and a float switch to activate the pump as the water level rises. In some cases the pump power cord simply plugs into a convenience receptacle. Other pumps are permanently wired into place.

The discharge line is often black polyethylene pipe. There is no vent pipe on a sump pump because the top is not tightly sealed. Sewer odors are not an issue because we are dealing only with storm water, not with waste from plumbing fixtures. Many sump pumps have a check valve. It can be integral to the pump or in the discharge pipe.

Sump pump pipes might discharge

into a storm sewer or combination sewer

into a ditch

onto the ground, well away from the home

into a French drain (gravel pit below grade)

out through a hillside if the ground slopes down away from the house (ravine lot, for example)

Discharge pipes from sump pumps that run outdoors are often buried just slightly below grade. In areas where the soil freezes in the winter, the pipe must slope continuously down away from the house so the water will drain out of the pipe. If water collects in low spots of the pipe, the water may freeze and block the discharge.

Since sump pumps are not tightly sealed, and are only designed to pump liquids, they are far less expensive than sewer ejector pumps. Because they play an important role, particularly in wet seasons, many people keep a spare pump on hand. In some cases, the sump is large enough to house two pumps. The redundancy of the two pumps can be handy.

Testing a Sump Pump

You can test a sump pump if there is some water in the sump. Running a pump with no water can damage the pump. Many sumps have no floor and the water may leach quickly out of the sump, preventing the pump from being flooded. You may waste a lot of time trying to get enough water into the sump.

If there is water in the sump, the pump can be tested by removing the cover and raising the float switch. Many of these use a dual float system.

Note: there is an electric shock hazard here since we have electricity and water together

. Use a voltage detector to ensure that the pump casing and controls are not electrically live before testing. Also, use a wooden stick to raise the float, or some other device that electrically insulates them from the pump. All sump pumps should be electrically grounded and, although not a requirement in many areas, a GFCI (ground fault circuit interrupter) protected circuit makes good sense. We talk about these devices in the Electrical Module.

When the float switch is lifted, the pump should start. If you can trace the discharge pipe, you may be able to find the termination point and ensure that water comes out the end of the pipe. In many cases, there won't be enough water in the sump to run the pump long enough to discharge water out the end of the pipe. In other cases, you won't be able to find the discharge point. You should describe this limitation to your client. Even if there is no water in the sump, many inspectors will lift the float switch very briefly to ensure that the motor turns over. While this isn't a rigorous test, it does give you some indication that the pump will respond when called for. Let's look at some of the problems you may find.
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by Manage My Life
April 26th, 2007
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