Is It True? Are Two Pumps Better Than One? – Part 2

Posted by in Basements | March 19, 2012

Our previous article, Part 1 of Is it True?  Are Two Pumps Better Than One? discussed some of the issues of a foundation drainage system that uses a sump basin to collect ground water and a pump to discharge the collected ground water.  In this article we offer two possible solutions to those issues.  We begin by noting that there are many options to consider in a backup pumping system for foundation drainage.  This article only discusses two of them.

12 Volt Deep Cycle Battery Powered Sump Pumps

The most common type of backup pumping system uses a pump with a battery.  A pump with a battery engages automatically when the float senses that the primary pump is not keeping up with water accumulating in the basin.  This is accomplished by setting the float for the backup pump slightly higher than that for the primary system.

When considering battery backup system, it is important to look at the pumping capacity or the flow rate in gallons per minute and the pump head in feet of water.  It does no good to install a pump that cannot produce enough pressure to move sufficient amounts of water up and out of the basement.  In general, the deeper your basement, the harder the pump works, and the smaller the water outflow.

Also note that all batteries are not created equal.  One or possibly two deep cycle 12 volt batteries (not a standard car battery) with as much amp hour reserve as practical are needed.  During the battery selection process consider how many hours the pump might need to operate, before the failure in the primary pumping system is noticed and addressed.  Fortunately, these systems use automatic battery chargers to keep the batteries topped off without human intervention.  So, if the power goes out for a few hours one day and the backup pump is needed again the next, the battery will probably be fully charged and available.


Figure SP-2 An example of a battery power backup sump pump. (Note however, that it is preferred to have a separate discharge line for each pump.)


City Water Powered Sump Pumps

If you live in an area where the power is unreliable you may consider a pump that utilizes a power source even more reliable and long lasting than the electric grid, that is, the municipal water supply.  But before selecting this type of pump, measure the water pressure at an outside spigot with a gauge that can be obtained at the local hardware store.  Water powered pumps are more efficient when higher pressures are available.  Consider also the effect of a pressure reducer that may have been installed on the inside water lines.

Knowing the water pressure helps to determine which pumps can be considered.  All water pumps are not equal.  Some are much more efficient and move a lot more water than their less expensive competition.  So, investigate how much water a pump can move for the given site conditions.  A deeper basement and a lower city water supply pressure will limit the available selection of adequate pumps.  Consider also that the pump placement location can vary since some water powered pumps mount at the sump basin while others attach near the basement ceiling.  So, if you have a small diameter sump basin which cannot accommodate two pumps, you still have options.  See Figures SP-3 and SP-4.

One downside of the best water pressure powered pumps is that it may not be obvious that they have been operating until a big water bill arrives.  Water power is definitely not cheaper than electric power!



Figure SP-3 A city water pressure powered sump pump mounted at sump basin.



Figure SP-4 A city water pressure powered sump pump mounted at the ceiling.


Lastly, ever wear a belt and suspenders?  Probably not, but depending upon your needs and how expensive the furnishings are in your basement, you might consider a dual backup design which incorporates the best features of both the battery and the water powered backup pumps, thereby increasing pump flow capacity and increasing the life of the batteries.

The conclusion is that there are definitely a lot of options from which to select.  And be advised that nearly all backup pumping systems utilize a pump that has a lower pumping capacity than the primary pump or that has a power source that is not as long-lasting or as reliable as the electric power from a household outlet.  In any case, you have been armed with some information, but it is probably not a decision to be made without consulting with a professional for additional options and proper installation, unless of course you are a qualified and experienced plumber.

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