Monday, June 1, 2009

Sump Pumps


Too much moisture in a home can lead to mold, mildew, and other biological growth. This in turn can lead to a variety of health effects, but it is mold and mildew I fear. Mold and moisture are the enemies of book collections and beneath my house in what most people would call a basement is the Library. It is home to my husband’s collection of books that he has spent 40 years assembling from every used book sale he has every hunted down or that we traveled to on vacation. While there are no first editions of note, there are things like the $2 used book he found in and old part of St. Louis which is worth many times that.

An unfinished, dry, partial daylight basement was a selection criterion for this house. There are steps that can be taken to minimize or eliminate water intrusion into a basement and they will be discussed in more depth on later posts, but since it was my intention to finish the basement as a library, we selected a house with a dry basement. The house which was only a few years old had been vacant for about seven months with the power shut off so I had the opportunity to see how the basement did through the spring without the sump pumps operating. The ground slope was less than optimal but good and the water table below the basement level.

The house has two sump pumps, one in the northeast corner of the basement and the other in the south east corner. The natural slope of the site is from the north west to the south east. Like most newer houses in the northeast United States, the basement slab is poured over a bed of about a foot of gravel stone into which are buried drain tiles that are (hopefully) pitched toward the sump. The drain tiles may extend under the entire basement, just along the footings or only in the area of the sump pumps depending on local codes and site considerations. These days drain tile is usually perforated plastic pipe run around the interior and exterior perimeter of the house. At one time clay tile was used and the name is retained from those days. The sump is a two foot diameter hole that should hold around 15-25 gallons of water.

A sump pump lifts the water up and out of the sump through a pipe that extends outside the house at ground level. There are two basic types of sump pumps, the pedestal and the submersible. The pedestal pump has the motor on top of the pedestal and is visible above the floor surface. The motor on a pedestal pump is turned on and off by a ball float. The on/off switch is visible so that it can be checked. Submersible pumps are designed to be sit at the bottom of the sump and is activated by a ball float or a sealed mercury switch. Both types of sumps have a check valve on the water outlet pipe to prevent flow back when the pump is shut off.

Most sump pumps are turned on automatically when water level in the sump rises. Why have a sump pump if you wait until flooding has occurred to turn it on? There are three types of switches: a float, a pressure and mercury activated floating switch. Mercury switches have been phasing out. Since 2004, many states have passed legislation restricting the sale of mercury-added switches and relays, including float switches and tilt switches. As more of these state laws go into effect, mercury use in switches will likely decline. The following states currently have restrictions on the sale and/or distribution of mercury-containing pumps: Connecticut, Louisiana, and Rhode Island. In addition, California, Illinois, Maine, Massachusetts, Minnesota, New Hampshire, New York, and Vermont restrict the sale and/or distribution of pumps that contain a mercury switch as a component.All pedestal sump pumps are activated by a float activator (a ball valve just like in a toilet rises and turns the motor on when the water rises). Submersible sump pumps are activated by either a pressure sensor (water has more pressure than air so that when the water rises to cover the switch the motor turns on), or a floating switch.

Both types of sump pumps are centrifugal pumps. They use impellers to force the water to the sides of the pipe creating a vacuum at the center which sucks in the water. You’ve seen this with the functioning of an immersion blender. The typical sump pump is sized at either 1/3 or ½ horsepower. A larger motor is needed to lift water to a higher level.

Soil conditions, groundwater level, rain and siting aspects of the property will determine the amount of time that a sump pump will operate and the number of pumps necessary to keep a house dry. Many houses with limited issues are built with one sump pump to handle occasional or seasonal problems. Sump pumps are powered by electricity and often it is recommended that a ground interrupt plug is used because you have water and electricity coming together. There are two problems with that. The first is that the pump needs to be regularly checked to make sure the ground interrupt has not been tripped, ground interrupt plugs trip at the wall. Without checking, only failure of the sump pump (flooding) would indicate that the plug failed. The second problem is power interruption. Sump pumps are often most needed during and after rain storms. This is a time when power often fails. Without power the typical sump pump will not operate. A battery backup system is the most common type of backup and should be seriously considered for any installation where the dryness of the basement matters. Running a sump pump on a backup generator is another possibility, and if your property runs on “city water” there are sump pumps driven by the municipal water supply pressure. They should only be used as back up pumps because they do waste drinking water.

Sump pumps and backup systems need to be tested or checked regularly so that an equipment failure will be noticed before the system fails and the basement floods. At least annually the system should be checked for functioning.
• Check the plug to ensure that there is power to the pump motor
• Remove the lid from the sump and inspect the interior with a flashlight, look to make sure that the pump is upright.
• Slowly pour a five gallon bucket of water into the sump. The sump should automatically starts and the sump drains quickly.
• If your sump pump is a submersible one, the grate on the bottom should be periodically cleaned of any gravel debris that might have been pulled into the pump.
• Know where your discharge pipes are and ensure that that are unblocked. They can become blocked with garden debris.

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