What a non-return valve does
A non-return valve is a valve in the drain pipe that lets water through in one direction only. When wastewater flows normally towards the sewer, it pushes the valve open. When the water in the sewer rises and tries to flow back, it presses the valve shut. That way the sewage stays in the pipe and out of your cellar.
The principle is simple, but how well it works depends on the right choice and position. A valve that does not close fully because of dirt or build-up does little when water levels are high, and a valve in the wrong place can also hold back your own drainage.
When is a non-return valve worthwhile
A non-return valve is mainly for drain points below the so-called backflow level, the level the water in the public sewer can rise to during a downpour. In practice this means:
- a cellar with a floor drain, washing machine connection or toilet
- a basement with a bathroom or kitchen
- an integral garage or storage room with a drain below street level
- homes in a low-lying street with a combined system
- properties where sewage has come back up before during heavy rain
In many municipalities the backflow level is taken to be street level. The exact requirements and advice vary by municipality, so it is sensible to check there.
Types
There are simple valves fitted into a straight pipe and versions with two valves in a row, one of which can be closed by hand. Drains that carry foul water, such as from a toilet, have different requirements from a pipe that only carries grey water from a washing machine or shower. For drain points well below street level, owners sometimes choose a pump chamber that pumps the water up above the backflow level.
Which solution suits you depends on the layout, the type of wastewater and the existing pipes. An installer can advise you and fit the valve in line with the applicable standards.
Where the valve goes
It is important that the valve only protects the low drain points. Drains from upper floors and the rainwater drain should preferably connect to the sewer before the valve. If they do come out behind the valve, water from above cannot get away when the valve is closed and still flows into the cellar. The valve also needs to be easy to reach, for example in a chamber or behind an access hatch, so it can be checked and cleaned.
Maintenance: a valve must move freely
A non-return valve sits in a pipe carrying wastewater, so grease, hair and paper can cling to it. A valve that sticks half open will not close when water levels are high. A valve that sticks in the closed position holds back your own drainage. That is why it is usually recommended to check and clean the valve at least once or twice a year, and more often if the pipe carries a lot of grease or debris.
It also helps to keep the pipe before and after it clean. Periodic cleaning with high pressure jetting prevents build-up from collecting right up to the valve.
What Bosmans can do for you
If you are considering a non-return valve, it makes sense to first know how the pipes in your property run. With a CCTV drain survey, a Bosmans Rioolservice engineer maps the drainage: where the low points connect, what the fall is like and whether there are sagging sections or open joints. With that footage, you and your installer can make a well-founded choice.
Bosmans also provides drain cleaning and preventive jetting, so the pipe around the valve stays clean. For a blockage in a cellar drain, the 24/7 emergency service is available on +31 85 200 93 27.