Pump shutdown and valve slam When a pump shuts off, the liquid column in the discharge line keeps moving briefly under its own inertia, then reverses. A swing gate or flap valve caught in that reversal slams shut with an audible bang. The noise is the symptom, but the real concern is the load behind it. In larger systems with hundreds of valves, repeated slamming can fracture flanges, stress pipe supports, and, over time, rupture piping. A duckbill handles the same reversal differently. Its flexible body absorbs and damps the energy of the returning flow, and the lips close progressively instead of all at once. This effectively eliminates water hammer and π www. valve-world. net Valve World November 2026
When a check valve reaches the end of its service life, replacing it with the same design may seem like the simplest option. But changing operating conditions, maintenance demands and installation constraints can make it worth reconsidering the choice. This article compares rubber duckbill valves with traditional metal designs and examines what to consider when specifying a replacement.
By Cal Hayes, General Manager at Proco Products
About the author
Cal Hayes, General Manager at Proco Products, has more than 40 years of experience designing, studying, and patenting duckbill valves.
Many check valves in service today were selected long before the current operations staff. When a flap gate on a stormwater outfall or a swing check in a lift station wears out, it is usually replaced with an identical unit because the drawings call for it and the part number is already on file. However, it is a perfect opportunity to review your options. Across water, wastewater, stormwater, and industrial systems, rubber duckbill check valves are increasingly replacing metal flap gates and swing gates. A check valve passes flow in one direction and blocks it in the other. What separates the designs is how they behave over years of pump cycles, tidal back pressure, solids, and salt. The wrong choice, or an outdated one, can lead to valve slam and water hammer, clogged outfalls, corroded hardware, repeated maintenance calls, and systems that fail ahead of schedule.
How a duckbill works
A duckbill check valve is a single elastomeric body. Its outlet narrows to flat, pinched lips shaped like a duck’ s bill. Forward pressure
CHECK VALVES
Rethinking the check valve at replacement time
Duckbill check valves are ideal for situations where the existing outfall is close to the ground.
pushes the lips apart, and they open in proportion to the flow rate. When flow stops or reverses, the rubber’ s natural elasticity draws the lips back together into a leak-free seal. The valve has no hinge, no mechanical moving parts, and no seals to replace. The entire body flexes in response to the pressure differential, so nothing can rust or seize.
Where metal valves struggle
Pump shutdown and valve slam When a pump shuts off, the liquid column in the discharge line keeps moving briefly under its own inertia, then reverses. A swing gate or flap valve caught in that reversal slams shut with an audible bang. The noise is the symptom, but the real concern is the load behind it. In larger systems with hundreds of valves, repeated slamming can fracture flanges, stress pipe supports, and, over time, rupture piping. A duckbill handles the same reversal differently. Its flexible body absorbs and damps the energy of the returning flow, and the lips close progressively instead of all at once. This effectively eliminates water hammer and π www. valve-world. net Valve World November 2026
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