OTHER TOPICS | Valves
The Benefits of Rubber Duckbill Check Valves
Exploring the advantages and applications of elastomeric duckbills.
Cal Hayes | Proco Products
Check valves are workhorses in any pumping system. Their job is straightforward: to let flow go one way and stop it from coming back. While they are simple in function, choosing the wrong check valve or sticking with an outdated design can result in valve slam, water hammer, clogged outfalls, corroded hardware, costly maintenance calls and premature system failure. Rubber duckbill check valves are a beneficial option across water, wastewater, stormwater and industrial applications.
What Is a Rubber Duckbill Check Valve?
A rubber duckbill check valve is an elastomeric, one-piece valve shaped like a duck’s bill—flat, pinched lips at the outlet end open under forward flow pressure and seal shut against backflow. Unlike a swing gate or flap valve, there are no moving mechanical parts, no hinges, no seals to replace and nothing to corrode or seize. The entire valve body flexes and responds to pressure differentials naturally.
When fluid flows forward through the valve, the lips open proportionally to the flow rate. When flow stops or reverses, the natural elasticity of the rubber causes the lips to pinch shut, creating a positive, leak-free seal.
| IMAGE 1: Rubber duckbill valves are available in slip-on (pictured), flanged inline and flanged end-of-line configurations (Images courtesy of Proco Products)
Key Advantages
- Elimination of valve slam and water hammer: Valve slam is a widespread and costly problem in water and wastewater systems. When a pump shuts off, the column of liquid moving through the pipe continues briefly due to inertia, then reverses. In a traditional swing gate or flap valve, this reversal slams the gate shut with a loud bang. In larger systems with hundreds of valves, that bang can fracture flanges, stress pipe supports and over time cause ruptures in the piping system. Rubber duckbill valves do not slam. The flexible elastomeric body absorbs and dampens the energy of reversing flow. The lips close progressively rather than slamming shut, effectively eliminating water hammer and protecting both the valve and the surrounding infrastructure. In noise-sensitive environments such as indoor pump stations or near residential areas, this is particularly beneficial.
- No rust, corrosion or biological fouling: In saltwater, wastewater and chemically aggressive environments, steel and iron flap gates are prone to deteriorating even with protective coatings. Rubber duckbill valves are immune to rust, and quality elastomeric valves are also resistant to algae and barnacle growth. For marine outfalls and tidal applications where biological fouling on a metal valve can prevent it from sealing properly, rubber check valves are often a good option. Duckbill valves also perform reliably across a broad temperature range, maintaining flexibility and seal integrity and not warping, cracking or seizing.
- Self-cleaning, sloping bottom: Some duckbill valve designs feature a sloping bottom that allows complete drainage of the valve body after flow stops. This is important in wastewater and stormwater applications, where solid-laden flows would otherwise accumulate in a flat-bottomed check valve, which can lead to clogging and odors, requiring more maintenance. The sloping design ensures that solids—such as rags, grit or debris—pass through rather than settling.
- Safety and community benefits: Traditional open-throat flap gate valves can be hazardous because they are large enough for children or animals to crawl into, creating entrapment risks in municipal drainage and outfall structures. Rubber duckbill valves, with their pinched-shut lips at rest, eliminate this risk.
- Installation flexibility: Rubber duckbill valves are available in slip-on (end-of-pipe), flanged inline and flanged end-of-line configurations. This flexibility makes them useful in retrofit situations where the existing outfall invert is close to a floor or concrete pad, leaving little room to install a rigid flat-bottomed valve. These valves can often be installed without expensive structural modifications to the existing manhole or outfall structure.
| IMAGE 2: Installing a rubber duckbill check valve in Dubai, UAE
Ideal Applications
Rubber duckbill check valves are well-suited for:
- Municipal stormwater and combined sewer overflow (CSO) outfalls that discharge to rivers, creeks and coastal waters
- Wastewater treatment plant effluent discharge points
- Sanitary sewer overflow (SSO) structures
- Marine and tidal outfalls subject to saltwater, barnacles and variable back pressure
- Industrial discharge systems with corrosive or chemically aggressive flow streams
- Water and wastewater pump stations where valve slam and water hammer are recurring problems
- Drainage structures near residential areas where noise is a concern
- Mine tailings outfalls
They are less appropriate in high-pressure, high-velocity applications exceeding 8 feet per second, where abrasion becomes the dominant wear mechanism for any valve type.
Selecting a Rubber Duckbill Check Valve
Not all duckbill valves are created equal. It is important to consider the following selection criteria:
• Flow rate and velocity: Know the gallons per minute (gpm), liters per second (l/s) or gallons per hour (gph). Velocity above 8 feet per second increases wear on any check valve. Match the valve’s full-port bore to the pipe diameter to minimize head loss.
• Back pressure rating: Understand the differential pressure the valve must withstand. Submerged installations in tidal or creek environments will see continuous back pressure. Select a valve rated for that specific condition.
• End connection style: Slip-on valves mount at the end of a discharge pipe. Flanged inline valves install midsystem. Match the connection style to the installation geometry.
• Elastomer compound: Standard chloroprene rubber and ethylene propylene diene monomer (EPDM) work well for fresh water and wastewater. Natural rubber or other specialty compounds may be required for marine, chemical, mining or fire-retardant applications. There are also fire-resistant elastomers.
• Sloping bottom vs. flat bottom: For solids-laden flows, a sloping bottom is recommended. The slope bottom ensures zero standing stagnant water. Full-port designs further reduce head loss and improve flushing efficiency.
• Flush ports: Flanged inline duckbill valves with flush ports on the top and bottom allow maintenance teams to clear any obstruction without dismantling the valve. This is an advantage over swing gate designs.
• Environmental resistance: For marine outfalls, specify algae and barnacle resistance to get the right material. Confirm temperature ratings if the valve will see extreme heat or cold.
| IMAGE 3: Diffusers with a flare-shaped bill are used in wastewater or outfall systems to help spread the discharge
Replacement as an Opportunity to Upgrade
When the time comes to replace aging flap gates or swing gate check valves in outfalls, pump stations or drainage infrastructure, do not simply reorder the same valve that has always been used; consider all options. Ask a local manufacturer for input on engineering data and to provide charts and graphs that answer questions and allow the user to specify the product and assist in elastomer selection.
Also, check to ensure the supplier has the correct type of valves in stock or readily available. There is nothing more frustrating than having a supply issue when the project and team are ready to go.
Cal Hayes is general manager at Proco Products and has over 40 years of experience in the design, studies and patents of duckbill valves. For more information, visit procoproducts.com.
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