Backwater valves are installed in the main sanitary waste piping line from the building to the sanitary waste line on the property, hence they are called in-line backwater valves. They are valves that are installed in your sewer line for the purpose of closing off the pipe when water tries to back up through it; they permit sewage to pass through in only one direction.
There are two basic kinds of backwater valves. One is called the main in-line backwater valve and is installed on the main sanitary line as it exits the building. The other kind is installed on individual floor drains, shower drains, and fixture drains. Of the main in-line type, there are two different classifications of quality. One is PVC, which is a less expensive material. Due to their light weight, PVC valves are relatively inexpensive. The other kind is usually longer lasting and has a cast iron valve body with a bronze valve. Due to the back pressure which can occur in the case of a flood, the cast iron kind are recommended for their ability to withstand greater pressures. If an area in which the valve is to be installed is not prone to flooding or has never flooded, then the less expensive type may be utilized safely. Check with local water authorities and civil engineers to determine the probability of flooding in your area.
Cities and municipalities are responsible for cleaning and inspecting sewer main lines and fixing or repairing lines which are damaged. It is also their responsibility to replace inadequate lines with larger ones when required. However, even if proper maintenance is done, it is still possible for a sewer main to plug and, potentially, allow water and sewage to back flow up the service line and into dwellings. The backwater valve serves to prevent this sewage from backing up in the waste lines and coming out of floor drains, shower drains, toilets and sink drains.
With an excess of rainwater, sanitary systems are more prone to backing up. Some localities have combined the site storm water drain lines with the site sanitary waste drain lines. It is easy to see how these combined sewers are more susceptible to backing up. In the case of flooding, a sump pump and sump pit can prevent rainwater from flooding your basement. These would be used in conjunction with the backwater valve to protect your home.
The determination of whether a backwater valve should be installed in a building during construction should be the responsibility of the design team. Your design professional or plumbing contractor, independently or jointly, should determine whether or not a backwater valve is required. As a home owner you may request one even if your plumbing contractor has not intended to install one. The diagram below and corresponding text indicates what determines the need for it, although each locality may have additional requirements.
Prior to installation, the unit should be thoroughly inspected (see manufacturer’s written instructions). Check the o-rings for tears, cracks, or foreign matter. Make sure the floatation devices are in place on each side of the gate. Make sure the gate moves freely. The unit should be installed with the correct slope as determined by local codes, your design professional, and the manufacturer. Make sure it gets installed in the correct direction. The arrows on the device should be in the direction of the flow of waste toward the outside of the building. Care should be taken that fittings do not get installed within a specific distance from the inlet side of the valve to ensure its proper functioning and to ensure that laminar flow will be maintained. This may be waived in retrofit installations by the local authority having jurisdiction. Take the necessary precautions when applying waste piping solvent to the connections so that solvent does not enter the valve. Re-inspect the unit for foreign material which may have entered the unit during installation. Failure follow the manufacturer’s recommendations and good construction practices may result in a failure of the valve when it is needed to function.
Again, extra care must be taken in the case of a retrofit installation. Sometimes, due to space constraints, a main in-line backwater valve cannot be installed. When this determination is made, then the alternative is individual fixture backwater valves.
In retrofit installations, always run and test all fixtures to ensure that each one runs through the backwater valve, and nothing remains unprotected. Follow manufacturer’s written installation instructions when installing individual backwater valves. Again, failure to follow these instructions may result in failure when the device is needed most. Do not install if proper grade cannot be achieved.
Mainline backwater valves are designed to be virtually maintenance free. However, they are mechanical devices which sit in a sewage environment, and periodic inspections are required. To ensure the satisfactory performance of the backwater valve, follow the recommended inspection schedule, and always inspect after a flood.
If the valve becomes damaged, either by remodeling the building or by some natural disaster like an earthquake, it should be replaced. A redesign of the plumbing system can increase the load beyond the design of the waste system piping, and in this situation, also, the valve should be replaced.