Backwater also known as Backflow Valves
This article covers the basics of sewer backwater valves.
The normally closed backwater valve is no longer permitted to be installed on the main sewer lateral unless it is vented properly, which in most cases, not feasable. However, this valve can still be installed on branch lines like floor drains.
The normally open backwater valve has to be checked and cleaned of waste buildup every now and then to increase chance of protection. It’s a simple procedure.
Sewer Backwater valves only offer protection from the municipal street line. If your own service line gets clogged, then your own waste drainage will back up until you notice the problem. They offer protection from your neighbours, not your own drainage. Installing closed style valves on branch lines will effectively increase your protection (from your neighbours). Water alarms help too and should be a part of your defence.
This video is informative and covers this topic more visually. It looks to be a promotional type video for a Toronto company, but it covers the essentials of backwater valves and drainage.
If you need your valve checked and/or cleaned or you need consulting to help figure out why your valve failed you, call Jay’s Sewer & Drain Service.