Checking the Stormwater Backflow Challenge

Controlling stormwater is a growing challenge for utilities and municipal authorities as they look to mitigate the economic and health impacts of excess water. Choosing the right check valve is a key part of the stormwater solution.

For water utilities and municipal authorities, stormwater management is a growing challenge. Changing weather patterns as a result of climate change is prompting more intense events that are increasing the volume of snow and rain water entering water management systems. At the same time increasing urbanisation is reducing the capacity of the environment to absorb surface runoff. With impervious surfaces such as pavements and roofs preventing precipitation from naturally soaking into the ground water is increasingly directed into storm drains, sewer systems and drainage ditches. However, often aging drainage infrastructure can be overwhelmed and as a result, poorly managed stormwater can see flooding events with backflow into residential areas, office parks and commercial areas. Inevitably, such events result in significant problems. For example, flooding can cause erosion, turbidity due to suspended solids, property damage, and traffic disruption.

There are also potential health and environmental implications. In many urban environments, excess storm water is channelled into the existing sewage system where it can then overwhelm the network and cause backflows and flooding with contaminated water through Combined Sewage Outfalls (CSOs). Such outfalls are increasingly seen as a key source of poor quality water and can lead to the presence of bacterial and virus pathogens that may impact human health as well as the aquatic environment. Stormwater runoffs can also prove damaging to natural water courses by increasing pollution and nutrient concentrations.

Poorly controlled stormwater or backflowing sewage not only results in temporary flooding, it can also see an increase in the presence of standing water, itself a significant health hazard. According to the World Health Organization (WHO), for example, standing water can act as a breeding ground for mosquitos and the multiple diseases they can spread. Indeed, mosquito-borne diseases are among the world’s leading causes of illness and death today. The significant consequences of poorly managed stormwater runoff mean that many authorities, municipalities and utilities are looking to control any excess runoff more effectively.

Managing stormwater with check valves

Gray infrastructure, such as culverts, gutters and storm sewers are key infrastructure elements that help to control stormwater. Green measures such as increasing pervious surfaces that allow water to penetrate into the soil also play a role. However, check valves are used in all stormwater and wastewater systems. These simple passive devices allow the one-way flow of fluids but automatically close to prevent any backflow. Check valves rely on flow velocity or a pressure differential to operate without any manual or automated intervention. One of the key characteristics is the minimum pressure required to open the valve, known as the cracking pressure.

By controlling and preventing backflow, check valves prevent discharges from wastewater treatment plants, Sanitary Sewer Overflow (SSO), CSOs and other and outfalls from flowing back and contaminating clean water supplies. When properly specified and correctly operating, check valves can also help to prevent flooding and standing water, ensure water flows in the correct direction and prevent potentially damaging phenomena such as water hammer. In addition, check valves are widely used to control odours. They protect residential and commercial areas from the backflow of methane and hydrogen sulphide gases from sewer systems and wet wells for example. By providing reliable backflow prevention, check valves have saved millions in potential damage to homes and offices and vegetation.

However, some types of check valve are vulnerable to failure and wear due to their design or can become blocked with debris. Some check valves are vulnerable to corrosion for example, or the disc – which rotates on a trunnion – may wear or the valve seat may erode. Similar issues can affect ball and spring check valves where corrosion can prevent the valve gate from properly seating. Some kinds of check valves may also become jammed with debris. Consequently, corrosive fluids or abrasive materials such as suspended solids may cause flap and swing check valves to fail, seize or to work sub-optimally. As a result, they may not completely prevent backflow and other associated problems such as water hammer. Water can also accumulate at the bottom of some types of check valves, leading to the presence of standing water. It is also the case that maintenance on certain types of check valve can be expensive and difficult.

Choosing the right check valve

While some check valve designs are susceptible to corrosion, fouling and erosion, the duckbill type is constructed of robust rubber or other elastomeric material. As the name suggests, the duckbill valve is a one-piece flexible sleeve shaped like a duck’s beak that parts at the cracking pressure and recloses below this threshold. Any reverse differential pressure firmly closes the valve preventing any backflow. Duckbill check valves are ideal for stormwater applications because they are non-mechanical, have low losses and do not slam on closure. They are also resistant to organic contamination such as algae and barnacles and have no problem discharging flows containing suspended entrained solids, even those containing abrasive slurries. Suitably specified and manufactured of an appropriate elastomer, check valves are also resistant to corrosive materials and are fireproof. For example, ProFlex™ check valves contain nothing that can rust or corrode and can be constructed out of the ANSI/NSF-61 material suitable for drinking water. Such check valves will not warp and operate over a wide range of temperature conditions, from -65 to +250º F. Due to their extremely simple design and robust construction rubber check valves also require zero maintenance and exhibit a substantial life expectancy of the order of 35 to 50 years. This is far longer than the 5-10 years typical mechanical check valves. In addition, the 711/731 ProFlex™ valve includes a low slope design leaving the outfall close to the floor and are engineered to crack open at just a few inches of head. This allows full drainage through the valve and eliminates any potential problems with standing water.

Rubber check valves can be installed on pre-existing pipelines or other infrastructure and are often used to replace existing flap gates which have proved inadequate. An example comes from Long Branch city in northern New Jersey which experienced severe flooding during Hurricane Sandy in 2012. As water levels rose, the city’s drainage system allowed flow reversals and acted as a path for flood waters to re-enter the town. To prevent similar events in the future, the city upgraded its drainage system by retrofitting Proco ProFlex™ duckbill check valves approved by FEMA. As a result, the city is now far less vulnerable to flow reversals during extreme weather events. See more about preparing a city for storm water events

When check valves used in stormwater systems fail or don’t properly seal, they can allow backflow. It’s an event which can cause extensive damage to homes, offices, and streets and also potentially represents significant health and environmental impacts. With the challenge of stormwater growing, it is more important than ever to make the right choice on check valves.

Properly designed and operating check valves prevent flooding and standing water, control back pressure from wastewater treatment plants and outfalls, and ensure water flows through piping in the correct direction. You can learn more about eliminating standing water in check valves

You can see an animated example of how the right check valves help cites and suburban neighborhoods mitigate odors and prevent rising rain water, stormwater and sewage through manhole covers. See our video about using check valves in urban and suburban drainage

Proco Products are leading check valve manufacturers. See our range of rubber check valves here.