A
sump pump is a
pumpA pump is a device used to move fluids, such as liquids, gases or slurries.A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps...
used to remove water that has accumulated in a water collecting
sumpA sump is a low space that collects any often-undesirable liquids such as water or chemicals. A sump can also be an infiltration basin used to manage surface runoff water and recharge underground aquifers....
basin, commonly found in the
basement__FORCETOC__A basement is one or more floors of a building that are either completely or partially below the ground floor. Basements are typically used as a utility space for a building where such items as the furnace, water heater, breaker panel or fuse box, car park, and air-conditioning system...
of homes. The water may enter via the perimeter drains of a
basement waterproofingBasement Waterproofing refers to techniques used to prevent water from entering the basement of a house or other building. Effective below ground waterproofing will include both drainage and sealers....
system, funneling into the basin or because of rain or natural ground water, if the basement is below the water table level.
Sump pumps are used where basement flooding happens regularly and to remedy dampness where the
water tableThe water table is the level at which the submarine pressure is far from atmospheric pressure. It may be conveniently visualized as the 'surface' of the subsurface materials that are saturated with groundwater in a given vicinity. However, saturated conditions may extend above the water table as...
is above the
foundationA foundation is the lowest and supporting layer of a structure. Foundations are generally divided into two categories: shallow foundations and deep foundations.-Shallow foundations:...
of a home. Sump pumps send water away from a house to any place where it is no longer problematic, such as a municipal
storm drainA storm drain, storm sewer , stormwater drain or drainage well system or simply a drain or drain system is designed to drain excess rain and ground water from paved streets, parking lots, sidewalks, and roofs. Storm drains vary in design from small residential dry wells to large municipal systems...
or a
dry wellA dry well is an underground structure that disposes of unwanted water, most commonly stormwater runoff, by dissipating it into the ground, where it merges with the local groundwater. Often called a soakaway in the UK....
.
Pumps may discharge to the
sanitary sewerA sanitary sewer is a separate underground carriage system specifically for transporting sewage from houses and commercial buildings to treatment or disposal. Sanitary sewers serving industrial areas also carry industrial wastewater...
in older installations. Once considered acceptable, this practice may now violate the
plumbing codeA building code, or building control, is a set of rules that specify the minimum acceptable level of safety for constructed objects such as buildings and nonbuilding structures. The main purpose of building codes are to protect public health, safety and general welfare as they relate to the...
or municipal bylaws, because it can overwhelm the municipal
sewage treatmentSewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater and household sewage, both runoff and domestic. It includes physical, chemical, and biological processes to remove physical, chemical and biological contaminants...
system. Municipalities urge homeowners to disconnect and reroute sump pump discharge away from sanitary sewers. Fines may be imposed for noncompliance. Many homeowners have inherited their sump pump configurations and do not realize that the pump discharges to the sewer. If the discharge is fed to a laundry sink in the basement, it's likely going to the sewer.
Usually hardwired into a home's electrical system, sump pumps may have a
batteryAn electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
backup. The home's pressurized water supply powers some pumps, eliminating the need for electricity at the expense of using potable water, potentially making them more expensive to operate than electrical pumps and creating an additional water disposal problem. Since a sump basin may overflow if not constantly pumped, a backup system is important for cases when the main power is out for prolonged periods of time, as during a severe storm.
There are generally two types of sump pumps —
pedestal and
submersible. The pedestal pump's motor is mounted above the sump, where it is more easily serviced, but is also more conspicuous. The pump impeller is driven by a long, vertical extension shaft and the impeller is in a scroll housing in the base of the pump. The submersible pump is entirely mounted inside the sump, and is specially sealed to prevent electrical
short circuitA short circuit in an electrical circuit that allows a current to travel along an unintended path, often where essentially no electrical impedance is encountered....
s.
Sump pump systems are also utilized in industrial and commercial applications to control
water tableThe water table is the level at which the submarine pressure is far from atmospheric pressure. It may be conveniently visualized as the 'surface' of the subsurface materials that are saturated with groundwater in a given vicinity. However, saturated conditions may extend above the water table as...
-related problems in surface soil. An
artesian aquiferAn artesian aquifer is a confined aquifer containing groundwater under positive pressure. This causes the water level in a well to rise to a point where hydrostatic equilibrium has been reached. This type of well is called an artesian well...
or periodic high water table situation can cause the ground to become unstable due to water saturation. As long as the pump functions, the surface soil will remain stable. These sumps are typically ten feet in depth or more; lined with corrugated metal pipe that contains perforations or drain holes throughout. They may include electronic control systems with visual and audible alarms and are usually covered to prevent debris and animals from falling in.
Components
Modern sump pump components in the United States are standardized. They consist of::
- A plastic, metal or concrete container forming a sump basin, approximately 2 feet (0.6 m) across and 2 to 3 feet (0.6 to 1 m) deep, 15 to 25 U.S. gallons (60 to 100 litre) capacity;
- A sump pump, either 1/3 or 1/2 horsepower (200 or 400 W), either battery or electrically powered (or both);
Pump selection
The selection of a sump pump will rest heavily on the application in which it will be used. To select the appropriate sump pump, consider the following:
- Automatic vs. manual operation — Selection of a manual sump pump means that one will turn the pump on and off when appropriate. Selecting an automatic sump pump means that a switch is wired to the sump pump to turn it on or off at appropriate water levels. Automatic switches include pressure switches, low level pressure switches and float switches.
- Power — Sump pump motive power will vary from 1/4 horsepower to multiple horsepower.
- Head pressure — The head pressure of a sump pump describes the maximum height that the pump will move water. For instance, a sump pump with a 15 ft maximum head (also called a shutoff head) will raise water up 15 ft before it completely loses flow. Technically, head pressure is defined as an expression of a pressure in terms of the height of fluid; P = yρg, where y is the fluid column height, ρ is fluid density and g is the acceleration of gravity. Other considerations may be added to overall head pressure, including loss from elbows/bends and friction loss from long horizontal runs.
- Power cord length — It is important to consider the length of the cord of any special switches that may be connected to the pump. Running a more powerful electrical motor a long distance from the main service panel will require heavier gauge wires to assure sufficient voltage at the motor for proper pump performance.
- Phase and voltage — Sump pumps powered from the AC mains are available with single-phase three-phase motors. rated for 110-120, 220-240, or 460 volts. Three-phase power is typically not available in residential locations.
- Water level sensing switch type — Pressure switches are fully enclosed, usually inside the pump body, making them immune to obstructions or floating debris in the sump basin. Float switches, particularly the types attached to the end of a short length of flexible electrical cable, can get tangled or obstructed, especially if the pump is prone to movement in the basin due to torque effects when starting and stopping. Pressure switches are typically factory set and not adjustable, while float switches can be adjusted in place to set the high and low water levels in the sump basin.
- Backup system and alarm — If redundancy and an alert system are vital for operation of your sump pump, consider a backup system and/or alarm.
Backup components
A secondary, typically battery-powered sump pump can operate if the first pump fails. A battery powered secondary pump requires the following components in parallel with the above others:
- A battery-driven 12 volt sump pump with its own water level sensor, piping, and check valve (the pipes usually join after the check valves to prevent reverse flow through the primary when the secondary unit is pumping);
- A typical lead-acid battery. It may alternately be a marine deep cycle battery
A deep-cycle battery is a lead-acid battery designed to be regularly deeply discharged using most of its capacity. In contrast, starter batteries are designed to deliver short, high-current bursts for cranking the engine, thus frequently discharged of only a very small part of their capacity...
, or special long-life standby battery;
- A trickle-charge
Trickle charging, or float charging, means charging a battery at a similar rate as its self-discharging rate, thus maintaining a full capacity battery. Most rechargeable batteries, particularly nickel-cadmium batteries or nickel metal hydride batteries, have a moderate rate of self-discharge,...
battery charger. May alternately have a specialized controller to manage, monitor and test that the battery holding a charge.
Alternative sump pump systems can be driven by municipal water pressure. Water-powered sump pumps are similar to backup battery-driven systems with a separate pump, float and check valves. One can also use an
ejector pumpʎ̩An injector, ejector, steam ejector, steam injector, eductor-jet pump or thermocompressor is a pump-like device that uses the Venturi effect of a converging-diverging nozzle to convert the pressure energy of a motive fluid to velocity energy which creates a low pressure zone that dɯaws in and...
that uses an ordinary garden hose to supply high pressure water and another garden hose to carry the water away. Although such ejector pumps waste water and are relatively inefficient, they have the advantage of having no moving parts and offer the utmost in reliability.
If the backup sump system is rarely used, a component failure may not be noticed, and the system may fail when needed. Some battery control units test the system periodically and alert on failed electrical components.
A simple, battery-powered water alarm can be hung a short distance below the top of the sump to sound an alarm should the water level rise too high.
Maintenance
Sump basins and sump pumps must be maintained. Typical recommendations suggest examining equipment every year. Pumps running frequently due to higher water table, water drainage, or weather conditions should be examined more frequently. Sump pumps, being mechanical devices, will fail eventually, which could lead to a flooded basement and costly repairs. Redundancy in the system (multiple/secondary pumps) can help to avoid problems when maintenance and repairs are needed on the primary system.
When examining a sump pump and cleaning it, dirt, gravel, sand, and other debris should be removed to increase efficiency and extend the life of the pump. These obstructions can also decrease the pump's ability to drain the sump, and can allow the sump to overflow. The check valve can also jam from the debris. Examine the discharge line opening, when applicable, to ensure there are no obstructions in the line. Even a partially obstructed discharge line can force a sump pump to work harder and increase its chance of overheating and failure.
Resources
- Ann Cameron Siegal, "The Sump Pump's Fault, or Yours?", Washington Post, August 9, 2008
- "Sump Pump Helps Keep Water Out", North Dakota State University Extension Service, June 14, 2005
- Thomas Scherer, "Sump Pump Questions", North Dakota State University Extension Service
- "Sizing Up a Sump Pump" (pdf), University of Illinois Extension
- John Newton & Co. "Sump Pumps - Your Questions Answered"