A sump pump
is a pump
used to remove water that has accumulated in a sump
pit. A sump pit, commonly found in the home basement
, is simply a hole to collect water. The water may enter via the perimeter drains of a basement waterproofing
system, funneling into the pit, or may arrive because of rain or because of natural ground water, if the basement is below the water table level.
In some cases, a sump pump is used when a lower floor is below the municipal sewer lines, to pump greywater or blackwater waste from that floor to the sewer lines.
Sump pumps are installed particularly where basement flooding is seen as a problem, but are also used to ameliorate dampness where the water table is normally above the foundation of a home. Sump pumps send water away from a house to any place where it no longer presents a problem, such as a municipal storm drain or a dry well. Older properties may have their sump pumps connected to the sanitary sewer, but this is frowned upon now (and may be against the plumbing code) because it can overwhelm the municipal sewage treatment system.
Sump pumps are usually hardwired into a home's electrical system, and may have a battery backup. Some even use the home's pressurized water supply to power the pump, eliminating the need for electricity. Since a sump pit may overflow if not constantly pumped, a backup system is important for cases when the main power is out for prolonged periods of time.
There are generally two types of sump pumps: pedestal and submersible. The pedestal pump's motor is mounted above the pit, where it is more easily serviced but also more conspicuous. The submersible pump is entirely mounted inside the pit, and is specially sealed to prevent electrical short circuits.
Modern sump pump components in the United States are standardized. They consist of::
- A plastic or metal canister forming a sump liner, approximately 2 feet (0.6 m) across and 2 to 3 feet (0.6 to 1 m) deep, 15 to 25 US gallons (60 to 100 L);
- A sump pump, either 1/3 or 1/2 horsepower (200 or 400 W), either battery or electrically powered (or both);
- A set of pipes, typically 1.5 inch (38 mm) PVC, that are routed from the pump, through a check valve, and out of the house;
- A check valve allows water to flow up and out through the pipes, so when the pump turns off, the water in the pipes doesn't flow backwards back into the sump;
Optionally, some homes (especially ones with finished basements) have a secondary battery-powered sump pump in case the first pump fails. Setting up a battery backed-up secondary pump involves purchasing and installing the following components in parallel with the above others:
- A battery-driven 12 V 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 car battery. May alternately be a marine deep cycle battery, or special long-life standby battery, these are more expensive but run longer and have a longer life sitting idle;
- A typical trickle-charge car battery charger available at any automobile parts store. May alternately have a specialized controller to manage, monitor and test the battery to insure it has enough fluid inside and is holding the required charge.
Alternatives to battery driven backup sump pumps include:
- Sump pump system driven by municipal water pressure. These are similar to backup battery driven systems with a separate pump, float valve and check valve.
In the event your primary and backup system fail, you may be able to keep your sump well emptied using these methods:
- A water driven emergency pump. These are typically used to empty swimming pools. One commercial product is named the "pumps-a-lot".
- A gasoline powered 110V backup generator into which the sump may be plugged. This does require several manual steps such as positioning the generator outside, filling it with gas and running power cords. A typical sump may require 1200 watts of power to start so a 1500 watt generator would be required.
- A marine hand bilge pump and a bucket.
One of the problems with most backup sump systems is they are rarely used so a component failure will not be noticed and the system will fail to operate when needed. Some battery control units test the system periodically and alert for some failed components, mainly electrical. Backup systems should be tested monthly. A good time to test is just after a rain storm. Pull the plug on the sump pump so the sump well fills to verify the backup system activates and empties the well.
Do not place backup components on the floor. Should the system initially fail the over flowing sump well will most certainly damage the electronics.
A device every home with a basement should have is a simple battery powered water alarm. The water sensor can be hung a few inches below the top of the sump well and will sound a shrill alarm should the pumping system fail and the water level rise too high.
Sump tanks 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 highly mechanical, will fail eventually, which could lead to a flooded basement requiring costly repairs.
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.
- 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