Duckbill check valves are a type of backflow prevention device that uses a rubber duck bill-shaped flap to control the flow of fluid. They are also called flexible check valves, or slow closing rubber check valves and are designed to prevent backflow of liquid or gas through a piping system.
They are a passive, unidirectional, and flow-through valve that requires no external energy source or manual assistance to operate. They are a cost-effective solution to backflow control, especially when compared to mechanical disc or ball check valves that may require expensive and time consuming maintenance as they age.
The most common material used for a duckbill check valve is food grade silicone or rubber. These can resist abrasive slurries and are resistant to organic contaminants such as algae or barnacles.
These are typically available in a slip-on style that fits onto the end of a pipe or a flanged version that can be mounted on the end of a discharge pipe. A flanged version will often need an outer undercut to secure it in place.
They use a pressure differential between the upstream and reverse pressures to open or close. When the upstream pressure is greater than the reverse pressure, the duck bill flap opens and permits fluid to flow through the valve. Once this is achieved, the duck bill flap returns to its flattened position to prevent backflow.
Unlike other types of check valve, a duck bill flap doesn’t slam shut, which helps to prevent water hammer and noise. This is a key feature for many industries, including coastal waters, sewage and municipal water applications.
Other benefits of duckbill check valves include a simple design that does not need any moving mechanical parts to break down or jam, reducing operation costs and maintenance needs. They are rated to handle a variety of different fluids and have an operating temperature range from -65 to +250 degrees Fahrenheit.
Inline duck bill check valves are used to control the flow of a sanitary sewer or drainage system by preventing backflow of wastewater from a drain. They are a versatile option for a variety of applications, including water treatment plants, wastewater sewage, and pumping stations.
They are easy to install and are highly efficient, quiet, and tough. They are powered by line pressure and do not require an outside energy source to operate.
This means they are ideal for tidal systems and sewage treatment plants that rely on natural backpressure to control the flow of water or sludge. The flexible sleeve design of these valves ensures maximum flow with minimum pressure drop.
Another important factor to consider when selecting a duck bill valve is the minimum pressure that must be applied to open it. This is called the cracking pressure and is affected by the material hardness of the sleeve, rebound resilience, and the size of the slit.
When determining the minimum cracking pressure, a good rule of thumb is to compare the material hardness with the rebound resilience. Generally, higher hardness materials will have better rebound resilience and will open and close easier than lower-hardness materials.