plumbing question: what is the purpose of a "check valve"?

Why would one want to use a check valve for a sump pump. Is there any harm done to the pump if backflow occurs?

Public Comments

1. Check valves are usually installed to prevent backflow/excess flow.
2. it prevents contaminated water from going back into your system
3. It prevents the flow of water or liquid from going the wrong way in a pipe. It lets the liguid go through the valve but not backflow
4. One way valve, commonly used on sump pump output to prevent the water from flowing back into the pump.
5. no harm to the pump but backflow could end up where you don't want it.
6. we use check valves in refrigeration too., they are also used in a number of different applications. This link has some pretty good information on check valves check it out. http://en.wikipedia.org/wiki/Check_valve
7. It really depends on the codes in your city, but it would be a good idea to have a backflow valve in any plumbing system. However, it would be especially important to have with a sump pump. Since the sump pump is the lowest part in your plumbing system, if the city sewer line backs up then all the sewage will end up over flowing form the tank where the pumps and located in. Depending of the location of the sump pump, an over flow will cost thousands to clean up. So my point back flow good.
8. The premise of a sump pump system is you have a pit or some lowered spot that you want the water to drain into, and then pump that water out of the pit to another location. The reason you want the check valve is usually you are pumping the water to a higher location (that's the reason your using a pump and not just draining it by gravity). If you do not have the check valve, the water you put into the line could run back into the pit. This will result in either the sump pump constantly going on and off as it pumps the same water out, only to have it run back into the pit. Or worse, the added backflow could cause the sump pit to overflow, flooding the area around the pump.
9. A check valve only permits flow of liquids in one direction. Otherwise if the pressure drops, (pump shuts off), whats contained in the lines that did not make it to the discharge point will not be allowed to fall back past the check valve into the pump or the container in which it comes from. It can cause damage to the pump over time because the pump will be continuously be trying to push the same material through the lines putting more wear and tear on the pump. You also dont want the container being backfilled everytime the pump shuts off or if the system backs up and fills the pipe. It could overflow the container.
10. Besides all the excellent reasons cited above, the valve can also prevent mice from crawling into the pump and causing sticky problems.