Richard Bateman, Product Marketing Manager at RWC, looks at check valves and how they help prevent backflow before it becomes a serious issue.

Backflow can lead to serious problems, such as contaminated water, hazardous situations, and major disruptions, so homeowners need to ensure all preventions are in place – and that usually involves a call to their plumber. Backflow is caused by the differences in pressure between the mains supply and the household’s water system. 

Regardless of what causes this difference – it could be anything from a burst pipe to works on the mains – simple physics mean water flows back from the outlet and ends up in the home’s water supply. 

Technically, this process is called back-pressure or siphonage and any item can be affected, including garden hoses, washing machines, and dishwashers. That means that water contaminated with pesticides, detergents, and chemicals can end up being used in food preparation or for drinking, causing serious health risks to the user. 

So, how can you tell if it’s happened? Well, the tell-tale signs are pretty obvious and, if your customers are complaining about water that looks, smells, or tastes strange, then backflow is a very likely cause.

Quite apart from the obvious health risks, backflow can cause major disruption too. Systems have to be drained and thoroughly cleaned and, on the rare occasions water gets back into the mains, whole neighbourhoods could be locked down – and we’ve all had plenty enough of that already.

Backflow is a serious enough issue to warrant legislation. The 1999 Water Supply (Water Fittings) Regulations for England and Wales classify water in five fluid categories. All of them except Category 1 (clean safe water, unconnected to anything else) require the installation of devices to protect against backflow. 

Categories 4 and 5 (containing toxic substances dangerous to human health) are the most serious, often apply to buildings in public use, and require specialist valves. That leaves Categories 2 and 3 both of which are common within a domestic application. 

Fluid Category 2 defines water that’s changed in taste or appearance, probably as a result of micro-organisms or fluctuations in temperature. Fluid Category 3 presents a higher degree of risk, but not enough to be life-threatening. 

In both Fluid Categories 2 and 3, devices must be installed to protect against backflow. The most common form of devices is check valves, which simply act to ensure water flows only one way, therefore, preventing it from re-entering the system and helping keep households safe. 

There are a number of types of check valve. Type EA (verifiable) and type EB (non-verifiable) single check valves are used to protect against backflow in Fluid Category 2 applications. Similarly, type EC (verifiable) and ED (non-verifiable) double check valves are used in Fluid Category 3 applications. 

Double-check valves are typically two single check valves linked together, providing failsafe backup if one of the check valves fail for any reason. Double check valves also have screws on each side so that the valve port can be opened and cleaned, as debris can build up over time.

When you’re fitting a check valve, the first thing to know is which fluid category you’re dealing with – and this can be found on the water regulations website. In any case, we’d recommend double check valves for appliances which use hot water, cleaning products, or chemicals – and that includes swimming pools for anyone lucky enough to have one.

The correct backflow prevention is key, but it’s also important to understand where to fit any device specified. The device should be installed as close to the potential risk point as possible. A typical example would be a mixer tap that is ‘passing’ and allowing hot water back down the cold supply. 

This would be identified as a Fluid Category 2 contamination risk. A single check valve is recommended as an ideal solution. The valve must be installed to the cold supply as close to the tap as possible.   

Installing the device as close as possible to the risk is again essential when locating the device in Fluid Category 3 applications. An example is on the connection to an unvented hot water cylinder. 

Due to the potential of contaminated water passing from the cylinder back down the cold supply feed as it heats, it is essential that a Fluid Category 3 type device is installed – commonly a double check valve to the feed pipe – again as close to the potential risk site as possible. 

Backflow is just part of the job and, at some time or another, all plumbers will come across cases. As always, it’s best to prevent it from happening in the first place.