Is It True? Are Two Pumps Better Than One? – Part 1

Posted by in Basements | March 08, 2012

For decades foundation drain tile have been placed around basements of dwellings to collect and drain ground water from the soil, especially during and after a rain storm.  These drain tile are commonly comprised of short lengths of clay tile or perforated plastic pipe placed around the perimeter of the basement.  The pipes are placed just inside or just outside the basement wall with the top of the pipe set below the bottom of the floor slab.

If the city storm sewers are lower than the drain tile, or if the dwelling is near a down slope hillside, the collected ground water may be drained by gravity into the storm sewers or onto the hillside.  This type of foundation drainage system works well until the drain tile or the drainage pipe to the storm sewer or the hillside become plugged with soil, roots, vermin, etc.

However, if the city sewers are higher than the drain tile or there is no nearby hillside, the collected ground water commonly drains into a sump basin, where it accumulates and is pumped out when the sump pump is activated by a float sensor that monitors the depth of the water.  This type of foundation drainage system works well until the drain tile or drainage pipes become plugged, the sump pump fails, or the electricity goes out.  Many who have experienced failures with this type of foundation drainage system have been involved in a bucket brigade, mopping, vacuuming, and/or drying out a wet basement floor.

So, what can you do to be prepared for the next storm?  How about a backup system comprised of a second pump with all the accessories?  Some publications recommend that every home have at least two pumps in the sump basin.

Some sump basins have two pumps, both of which are powered by plugging into an electric outlet.  The second pump is a backup or supplementary pump that operates if the primary pump is inadequate or fails.   The inadequacy or failure of a primary pump may occur if a float switch contact goes bad; a break in a pipe routes excessive amounts of water to the footer drain; the discharge line becomes obstructed;  and/or the check valve on the discharge line stick opens and allows water once pumped out to flow back in.  Any of these issues may result is a wet or flooded basement where there is only one pump.  A second pump powered by an electric outlet can reduce the risk of a wet basement when one of these issues occurs.  However, this backup pump, when powered by an electric outlet, does not overcome the water accumulations resulting from a loss of power.

To resolve the latter, why not consider installing a backup pumping system powered by an alternate energy source?  Using a backup pumping system powered by an alternate power source can reduce the risk of a wet basement even further.  Such a backup pumping system includes a second sump pump, a float switch, and an alternate power source, such as, a battery or the domestic water supply system in the dwelling.  The effectiveness of a backup pumping system depends on the type of equipment selected, how it is installed, and the various local conditions present.  See Figure SP-1.

Pedestal-pump-and-submersible-pump-in-basin

Figure SP-1 Pedestal style sump pump and a submersible type sump pump in the same sump basin.

The next article (March 19, 2012) will discuss two options for a back up system.

This article was prepared by Thomas J. Kocka, P.E. of Thomas Engineering.