CHECK VALVES
protects both the valve and the surrounding infrastructure. Indoor pump stations and facilities near residential areas also benefit from the quieter operation.
Salt, chemicals, and marine growth Steel and iron flap gates deteriorate in saltwater, wastewater, and chemically aggressive environments, even with protective coatings. Rubber does not rust, and quality elastomeric valves resist algae and barnacle growth. On marine outfalls and tidal installations, where fouling on a metal gate can prevent it from sealing, the rubber valve is the better option. Temperature is a further consideration. Duckbill valves remain flexible and hold their seal across a broad temperature range, including conditions in which metal valves may warp, crack, or seize under thermal stress.
Solids that settle In wastewater and stormwater service, a flatbottomed check valve collects the solids that remain after flow stops. Rags, grit, and debris accumulate, leading to clogging, odors, and more maintenance. Some duckbill designs use a sloping bottom that drains the valve body completely, so solids pass through with the flow instead of settling.
Open throats and public safety A traditional open-throat flap gate can be large enough for a child or animal to crawl into, creating an entrapment risk at municipal drainage and outfall structures. A duckbill at rest keeps its lips pinched shut, which removes that hazard.
Tight retrofit geometry Duckbill valves are available in slip-on( end-ofpipe), flanged inline, and flanged end-of-line configurations. That range is useful in retrofits
Installing Duckbill Check Valve.
where the existing outfall invert sits close to a floor or concrete pad and leaves too little clearance for a rigid flat-bottomed valve. In many cases, you can install a duckbill without costly structural modifications to the manhole or outfall structure. Where duckbills fit and don’ t Rubber duckbill check valves are well suited to:
• Municipal stormwater and combined sewer overflow( CSO) outfalls discharging to rivers, creeks, and coastal waters
• Wastewater treatment plant effluent discharge points
• Sanitary sewer overflow( SSO) structures
• Marine and tidal outfalls exposed to saltwater, barnacles, and variable back pressure
• Industrial discharge systems carrying corrosive or chemically aggressive flow
• Water and wastewater pump stations with recurring valve slam and water hammer
• Drainage structures near residential areas where noise is a concern
• Mine tailings outfalls
They are a poorer match for high-pressure, high-velocity service above 8 feet per second, where abrasion becomes the dominant wear mechanism for any valve type.
Specifying the valve
Duckbill valves differ considerably in design and construction. The following criteria determine whether a particular valve suits a particular installation.
Flow rate and velocity: Establish flow in GPM, L / s, or GPH. Velocity above 8 feet per second accelerates wear on any check valve. Matching the valve’ s full-port bore to the pipe diameter minimizes head loss.
Back pressure rating: Determine the differential pressure the valve must withstand. Submerged installations in tidal or creek environments see continuous back pressure, and the valve should be rated for that specific condition.
End connection: Slip-on valves mount at the end of a discharge pipe, while flanged inline valves install mid-system. The installation geometry dictates the choice.
28” 730 Proco Duckbills with an enlarged soft cuff to fit over a 32” RCP pipe in Queensland Australia.
Elastomer compound: Standard chloroprene and EPDM perform well in fresh water and wastewater. Marine, chemical, mining, and fire-retardant applications may require natural rubber or other specialty compounds, and fireresistant elastomers are also available.
56 Valve World November 2026 www. valve-world. net