Single or double: Check valves and their applications

mixer tap with backflow

From contaminating water to hazardous situations and major disruptions – backflow in homes is bad news. The good news though is that there’s a quick and efficient way that you can help prevent it from happening and that’s by using the right check valves. In this blog, we’ll look at the various types, the applications they can be used for, and how they help.

Backflow is bad news

Backflow can lead to serious problems, so installers and homeowners need to ensure all preventions are in place. Backflow is caused by the differences in pressure between the mains supply and the home’s water system.

There are a number of differences that could cause this pressure 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 water outlet or appliance 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.

Floguards Single

Following Backflow Legislation

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) requires the installation of devices to protect against backflow.

Categories 4 and 5 (containing toxic substances dangerous to human health) are the most serious, and 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 such as RWC’s Reliance Valves Floguard, which simply act to ensure water flows only one way, therefore, preventing it from re-entering the system and helping keep households safe.

Knowing the different types of check valve

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 that use hot water, cleaning products or chemicals – and that includes swimming pools for anyone lucky enough to have one!

Plumber under sink installing check valve

Where to install check valves

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.

We’re here to help you get it right

Preventing backflow is a fundamental requirement of every plumbing and heating installer’s skillset. As always, it’s best to prevent it from happening in the first place, and RWC’s family of brands has developed a range of single and double-check valves to solve this problem – available across our JG SpeedfitReliance Valves and SharkBite ranges.

We’re also here to provide installers with the right advice and support to get the job done, and to keep homes and homeowners safe. If you need help with backflow prevention, contact us here.

Lee Halstead Headshot

Lee Halstead

Technical Sales Engineer - JG Speedfit/Reliance/SharkBite & JG Underfloor

About the author

As a seasoned professional in plumbing and heating, having earned City and Guilds Plumbing Craft and Advanced Craft certifications in 1991, I have dedicated myself to mastering the craft.

For over two decades, I operated as a self-employed plumbing and heating engineer, serving both residential and new build sectors.

In 2015, I transitioned into the role of a Technical Sales Engineer with RWC. In this capacity, I have leveraged my extensive field experience and technical knowledge to provide invaluable support and build strong relationships with customers. As a spokesperson for RWC, I am thrilled to share my expertise and promote the cutting-edge products and services we offer in the plumbing and heating industry.