Ground Bearing Slab and Basement: Non return valve

Besides flooding, drain overflow is the most common cause of water damage to residential and commercial buildings. Due to limited capacity, public sewers can often have problems effectively discharging flood water during periods of heavy rain. Although the mains sewage system has drainage basins and other redundancy systems, as soon as certain capacities are exceeded, sewage can accumulate and, in severe cases, flow back into houses – with dramatic, highly-unpleasant and expensive consequences.

Rooms below the backflow level are particularly affected by this type of water damage. If there are no effective backflow safeguards, wastewater is very quickly pressed, not only into basements, but often over floor slabs into living areas. The result: ground floor rooms and basement rooms can be partially flooded within a very short period of time. To limit consequences from a possible canal overflow, highly-effective solutions are available: backflow stops, backstop pumps and automatic lifting systems.

In the following article, we will talk through the merits of these measures.

© KESSEL AG

Solution 1 for ground bearing slab and basement for secondary usage:
Non return valves

Backflow stops are installed in the backflow-prone dirty water line. If water levels increase beyond a defined point in the duct system, the built-in shutter is activated. The backflow stopper closes the corresponding lines and the inflowing backwater is stopped. When the dammed sewage drains, the backflow opens once again. Backflow closures are differentiated between the connected wastewater free of faeces or faecal matter: In sewage-free wastewater, a mechanical backwater trap is used. This backflow stopper works with a mechanical flap closure, which is triggered by the backwater, as well as with a manually operated emergency seal. For faecal wastewater, an electrically controlled backflow trap must be installed. A probe measures the water level in the sewer pipe and when a certain level is reached, the backflow trap closes a motor-powered flap. This backwater stop should, for safety reasons and to increase protection, be equipped with an alarm function. This means that residents are warned not to use any more equipment which drains through this backwater stopper until the backflow has passed. In the event of power failures, this motor-operated shutter will switch to battery power which ensures permanent protection.

© KESSEL AG

Solution 2 for ground bearing slab and basement:
Automatic lifting systems or backstop pumps

In an automatic lifting system, wastewater from the individual drainage points is fed into the lifting station through the inlet pipe. As soon as a certain water level has been reached in the tank, the pump switches on automatically and feeds the wastewater through the pressure pipe via the backwater loop to the main sewer outlet where it can then drain freely.

Automatic lifting systems are advisable when there is no slope to the mains drainage system and are a necessity when low lying areas such as permanent residences or basements used for storing valuable assets, need to be protected.

Backwater storage systems are also useful for environments that need to be protected against backwater. In the event of back pressure, connected drainage points can still be used as the backflow protection pumps will remove backwater. These systems can only be used when there is an available slope to the main drainage system. In normal operation, the pump is not required due the wastewater being able to to drain naturally.

Not in non-return valves can have major consequences

Regardless of whether it is due to heavy precipitation, significant snowmelt, or after a burst pipe – elevated levels in sewers are far more common than expected. Narrow pipes, blockages, sewer damage or pump failures can also be the cause of an increase in wastewater. Even firefighting operations can cause excess wastewater. All of these situations lead to wastewater accumulating in the disposal canal and being forced back into connected service lines. There it can rise to the backwater level, which on flat terrain is the road surface and on sloping terrain is the upper edge of the next higher canal shaft. If there is no back pressure protection in such situations, damaging and expensive consequences are inevitable. Damage to personal property and possibly significant damage to the building fabric could result in costly new purchases and remedial measures. Therefore, when planning a new home, be sure to install a backwater protection system – the only way to avoid serious damage due to back-flushing wastewater.

In the case of new buildings, the installation of a backwater protection can be carried out during the floor slab installation. Backflow safety devices may only be installed in dirty, rainwater pipes where the drainage points are below the backflow level. It is important to note that back pressures must be regularly serviced to ensure constant working order.