This article explains how sump pumps are used in buildings, describes the types of sump pumps, and describes how sump pumps should be installed, inspected, and maintained. We explain the difference between a sump pump, simplex and duplex sump pumps, a septic effluent pump, a sewage grinder pump, and an effluent pump.
This article explains the various types of pumps and their purchase, installation, inspection, and maintenance.
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Sump pumps, which we discuss on this page, are designed to remove unwanted water, such as surface or ground water that leak into a building. Sump pumps only have to pump water, never solids. Sump pumps are normally used to pump clear liquid, such as ground water from a wet basement sump pit or graywater from a basement laundry sink.
Our sump pump photo (left) is not a wonderful installation, but you can see the pump motor (red arrow), pump float switch (orange arrow), and flexible pump discharge pipe (white arrow) clearly. The water inlet in tihs case is at the bottom of the pump assembly (blue arrow).
Sump pumps are light-duty and unlike septic or sewage pumps, sump pumps have no ability to pass solid debris other than perhaps fi
A sump pump is typically installed in a pit at the low end of a building's basement or crawl space floor or in another location where water needs to be removed such as in a boiler pit or an outdoor well pit. On occasion we find sump pumps installed outside of a building foundation to remove water from around the foundation of a poorly-sited (too low) building which has no natural drainage path to dispose of ground water by gravity.
In a bad building water entry situation water runs across the basement/crawl space floor into the sump pit where it is pumped away (after already wetting the building and inviting a mold contamination problem).
This condition pertains when water is entering a building through foundation walls, often because the roof drainage or surface runoff are directed right against the building foundation itself.
Keeping gutters and leaders working and correcting outside drainage errors are critical in keeping water out of a building. Doesn't it make more sense to prevent water from coming into a building than to let it in and then pump it out?
In our flooding basement photo at above left, notice that there is a flood-line about half way up that oil storage tank? The little sump pump shown in the white bucket in the center of our photo is never going to handle such a huge volume of water.
And even for modest water entry, the projection of that sump bucket lip above the floor level means water has to rise a few inches in this basement before it can even flow into the sump pit!
In a good situation, openings in the sides and bottom of the sump pit (photo at left) , or an under-floor drainage system direct subsurface water into the sump pit before the ground water level rises enough to send water into the building. Over several years of operation, and partly by pumping a little soil silt as it operates, a sump pump may actually improve the flow of under-floor water into the sump pit, thus reducing building water entry.
Septic pumps, sewage pumps, grinder pumps, and effluent pumps are not sump pumps, and they are discussed beginning
at Sewage Ejector Pump Grinder Pump.
The distinction among these pump types is important. Choosing the wrong pump can mean a short operating life for the pump, an unreliable system, and unnecessary expense.
There may be some confusion, depending on with whom you speak, because people don't always use just the right terms for construction or septic system parts - and the right sewage pump term, or right septic handling product versus the wrong one can be an important distinction.
Single submersible or pedestal sump pump: The photo on the left is what you're likely to see if your basement has a modern sump pump.
A pedestal type pump must keep its motor out of water and dry. Regardless of which type of pump we select, many installations require that only one single pump be installed.
We discuss the details of submersible and pedestal sump pump types below
at Four Common Types of Sump Pumps.
Duplex sump pumps: The photo at left shows a duplexed sump pump system using pedestal type sump pumps. This was a really wet basement - a single sump pump simply could not keep up. In this installation .
When a building footprint or foundation layout is complex, or where the building is constructed over both basement space and one or more crawl spaces, it may be necessary to install multiple sump pumps to protect these various areas.
In a single large basement whose floor did not slope uniformly to a single low corner, it may be more economical to install two or even more sump pumps in problem areas than to tear up the entire basement floor to install a sub-slab drainage system.
Duplex sump pumps are illustrated and discussed further
at Septic Pump Duplex System Designs.
Please see SEPTIC PUMP DUPLEX DESIGNS for details.
Reserve septic backup design: the backup pump never runs unless the primary pump has failed or is overloaded.
A simple installation provides a pump control float switch that turns on the backup pump only water in the pumping chamber reaches a level above that normally handled by the primary sump pump. This approach provides both pump backup and the ability to handle surges in building water entry loads on the sump pump system.
Alternating septic pump design: the two sump pumps are installed at the same location but are wired so that the pumps take turns, first one, and next cycle the other pump is turned on by the float switch.
This pump hookup is more common among septic pumping stations than among home sump pump de-watering systems, but it may be appropriate where a large volume of ground water has to be kept constantly out of a building.
An example we've seen was in the basement of a home on Long Island, NY in which the level of the basement slab was so low that flooding from Long Island sound would be nearly constant if the pumps failed.
The alternating sump pump approach has the advantage that both pumps are being exercised regularly, which reduces the chance of the ugly discovery that in the event you have to rely on a backup sump pump which has been sitting idle, waiting its chance to run, has in the interim, died.
The submersible sump pump motor is capable of working when entirely under water.
A submersible sump pump uses a float switch intended to turn the pump on when
ground water rises in the sump pit (or flows stupidly across your basement and into the pit) where it is discharged to a storm drain or the property surface.
Watch out for debris or wiring in the sump pit that block movement of the float switch - your sump may fail to turn on.
Above: battery charger for a battery-operated sump pump.
Below: a water-powered sump pump design in a pre-1900 home
Sump pumps that have been added to an older structure often pump their discharge to the ground surface where it runs to a storm drain or area drainage setting.
If you have such a system be sure that the sump pump discharge empties where it meets these criteria:
Typically most of us just buy a 1/4 hp or 1/2 hp sump pump and throw it in the pit and see what happens. But you can guesstimate the rate at which water is flowing into the sump pit by knowing the sump pit dimensions and observing how long it takes the pit to fill to a measured depth.
At Static Head of Water in the Well we give details of how to calculate the volume of liquid in a cylinder (if your sump pit is round) using pi (3.14) and the radius (1/2 the diameter of the cylinder) squared.
Volume cylinder = 3.14 x (water height in inches ) x (cylinder diameter in inches /2)2.
Example using an 18" diameter joint compound bucket as a sump pit, and assuming that it takes water 1 minutes to fill the pit to 1 inch..
Volume = 3.14 x (1 inch of water) x ( 18 / 2)2
Volume = 3.14 x 1 x 81 = 254 cubic inches of water rose in the sump pit in one minute
Water in-flow rate to the pit = 254 cubic inches per minute
Convert cubic inches to gallons as follows.
1 cubic foot = (12 x 12 x 12) cubic inches or 1728 cubic inches
254 cu.in. / 1728 = .15 cubic feet.of water flowing into the sump pit per minute
1 cubic foot = 7.5 gallons (U.S. Liquid)
.15 cu.ft. x 7.5 = 1.1 gallons of water flows into the pit per minute
This example let's us state a simple "rule of thumb" for joint-compund bucket-sized sump pits.
One inch of water in an 18-inch diameter joint compound bucket or sump pit = about 1 gallon of water
This means all you have to do is calculate the number of inches that you see water rise in your joint compound bucket sized sump pit in one minute - that's roughly the number of gallons per minute that water is flowing into the sump pit.
Sump pumps for residential use range in horsepower from 1/4 HP to xx. Typical sizes are 1/3 HP and 1/2 HP. Prices (2012) run from about $100. to $200. for submersible pump models. Pedestal pumps and light duty sump pumps may sell for less than $100.
Sump pumps are rated for several important factors including horsepower and pumping capacity in gallons or liters per hour - a figure that varies by pump lift height. An individual sump pump's capacity will vary depending on the height to whch it has to lift its discharge water (higher lift means fewer gallons per hour) and other factors such as diameter and number of elbows in the discharge piping.
Watch out: be sure to consider both the anticipated de-watering flow rate you'll need and the pump's lift requirements. Typically if you are pumping out of a basement sump pit to ground level that's more than 5 ft. but less than 10 ft. of lift. But installations that have to lift higher distances and/or pump over longer distances and through multiple piping elbows need a more powerful pump.
Table of Sump Pump Performance Capacities and Typical Ratings for Residential Use
Sump Pump Lift Capcity
Submersible or flat-on-surface sump pumps
|1/4 HP ||GPM||32||25||10|
|1/3 HP ||GPM||43||34||19|
|1/2 HP ||GPM||93||70||64||36|
|Pedestal style sump pumps|
|1/3 HP Pedestal ||GPM||50||36||10|
|1/2 HP Pedestal ||GPM||60||51||38||17|
Notes to the sump pump size table: (Note that pump manufacturers offer a wider range of types and capacities of pumps than just the examples listed here. Also pumps of the same HP or capacity may be produced using different materials suitable for different applications and with different durability.)
 Zoeller® Old Faithful Pedestal thermoplastic Model 81 1/3HP, maximum "shut off" head: 16 ft.
* Some manufacturers give sump pumping rates as "total dynamic head/flow per minute dewatering" in gallons per hour instead of gallons per minute. When comparing pumps be sure you are comparing the same units. Also, among some manufacturers such as Zoeller, some pumps can handle both de-watering jobs and sewage effluent, but the reverse is not the case, that is, models that are designed only for de-watering, such as pedestal and some sump pumps, should not be used for septic system applications.
See SUMP PUMP INSPECTION for a detailed sump pump inspection & troubleshooting guide.
Sump pumps on newly constructed buildings are often connected to the building foundation drain. We consider this a bad practice. It is a rare home more than 20 years old whose footing drains are intact.
If a footing drain discharge itself becomes clogged or damaged, sending the sump pump discharge into that system will not work: you'll simply flood another section of the building foundation, basement, or crawl space, or you may overload the existing foundation drain causing building water entry.
Connecting a sump pump to a municipal sewer drain is bad practice and illegal in some communities. You're adding to the municipal sewer plant's water overload during wet weather and you may thus be contributing to the discharge of raw sewage from the overloaded municipal treatment facility right into the environment.
Where permitted, we prefer to route a sump pump to a storm drain, or where soil conditions permit it might be discharged to a drywell.
If the sump pump motor is running or too frequently, constantly check the following:
Continue reading at SUMP PUMP DISCHARGE or select a topic from the More Reading links or topic ARTICLE INDEX shown below.
Or see SUMP PUMP TYPES
Or see SEPTIC SYSTEM PUMPS
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This was the most informative article I've read during my extensive online research on the topic of "Basement Flooding" (see BASEMENT WATER ENTRY PREVENTION) . Ground water/high water table has been determined the cause of water entry into my basement "pit" area underneath my main sewer trap. We have a Basement Watch Dog Dual Sump Pump with battery backup installed however the constant presence of groundwater in our pit continues to worry us.
Our Staten Island, NY home location is situated where the properties behind, to the left and right of us are elevated. PVC fencing with sealed bottom moulding prevents rain water from cascading over the concrete/paver surfaces; however it is our belief that the groundwater underneath from all three directions have found a hydrostatic relief in OUR PIT! What recourse do we have? Any advice you can give us would greatly be appreciated. - Joe Apap 09/2011
Thanks for the nice note, Joe; we've been working hard on wet basement and wet crawl space information, particularly since recent hurricanes and tropical storms have led to so much flooding.
The question you raise about the effects of a sump pump on soils, water flows, and by implication even the building foundation is an important one.
Indeed sump pumps as basement de-watering systems work better over time precisely because the ultra fine soil particles pumped away open improved water drainage passages towards the sump pit. One of the first sump pump installations I worked on back in 1969 was installed to reduce the entry of water that used to squirt into a basement through its walls during heavy rains. When the sump pump was first installed it did not immediately stop the water entry, though it reduced it.
After just a few years the sump seemed to keep the water table below the basement slab and no more water squirted thorough the basement walls even in wet weather. Of course other conditions could have changed as well.
I have not been able to find data, and I doubt there is reliable data, about the "reach" of sump pump water movement past the building where it is installed.
Surely sump pump water movement reach will be a function of local soil characteristics including particle size, density, water and ground water sources, and frequency of sump operation.
And water tables underground can fool you - they are not level flat but indeed follow terrain contours. Still I would not be surprised if being surrounded by higher properties means you are receiving their surface as well as subsurface runoff.
I've read a few reports that in areas of fine soils a highly active sump pump may remove enough soil fines to actually cause foundation settlement or tipping. But it may just be urban legend - I've seen reports but no hard data.
If it's cost justified you could consider a curtain drain around your property. Such a drain, a ditch to an adequate depth and filled with No4 crushed stone and perforated piping led to an outdoor pumping station could intercept water from neighbors and keep it away from your home. Your outdoor pumping station will need to be deep enough to be frost proof and it will need to discharge to an approved destination such as a local storm drain.
Earlier I thought of advising you to ask neighbors to be sure their roof drainage is not aimed at your property, but given the vagaries of people and inconsistent property maintenance, I suspect that's a waste of time.
Also see BASEMENT De-Watering Systems.
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