A sump pump is a pump used to remove water that has accumulated in a water collecting sump pit, commonly found in the basement of homes. The water may enter via the perimeter drains of a basement waterproofing system, funneling into the pit 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 table is above the foundation 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 drain or a dry well. Pumps may be connected to the sanitary sewer in older properties. Now, this practice may be against the plumbing code or at least municipal bylaws because it can overwhelm the municipal sewage treatment system.
Usually hardwired into a home's electrical system, sump pumps may have a battery backup. The home's pressurized water supply powers some pumps, 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;
Selecting the Right PumpEdit
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 you 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.
- Horsepower: Sump pump horsepower 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’ max head (also called a shutoff head) will pump water up 15’ before it completely loses flow. Technically, head pressure is defined as an expression of a pressure in terms of the height of fluid; P = ypg, where p is fluid density and y is the fluid column height. Other considerations may be added to overall head pressure, including loss from elbows/bends and friction loss from long horizontal runs.
- Cord Length: The cord length of a sump pump describes the length of the power cord. It is also important to consider the length of the cord of any special switches that may be connected to your pump.
- Phase & Voltage: Sump pumps are available in single and three phase. The voltages offered include 115, 230, and 460 volt.
- Backup System & Alarm: If redundancy and an alert system are vital for operation of your sump pump, consider a backup system and/or alarm.
A secondary, typically battery-powered sump pump can operate if the first pump fails. A secondary pump requires 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 battery. It may alternately be a marine deep cycle battery, or special long-life standby battery;
- A trickle-charge 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. These pumps are similar to backup battery-driven systems with a separate pump, float and check valves.
If the backup sump systems 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 few inches below the top of the sump well to sound a shrill alarm should 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