A duckbill valve is a plumbing component used to control the flow of water or other liquids within a pipe. These valves allow liquid to flow in one direction only within the pipe while preventing the flow of liquid in the opposite direction. This flow control technique helps to prevent unwanted materials from contaminating a water supply. They get their name from their appearance, which resembles a duck's closed bill under normal conditions. A duckbill valve may also be known as a check valve or backflow preventer in some parts of the world.
Each duckbill valve resembles a rubber nozzle or nipple with a flanged end. The nozzle consists of two lips or flaps that meet to form a point. The flanged portion of the valve fits snuggly around the walls of the pipe, and another pipe is connected over the nippled end of the valve. As water flows through the pipe, the pressure it creates forces the lips of the bill to open, allowing the water through. Due to insufficient pressure in the opposite direction, the lips cannot open to allow water to flow in the opposite direction.
The most common duckbill valve models are made of elastomeric materials, and are designed for general-purpose applications. Special coatings or materials are used to create food-grade valves, as well as valves used in medical settings. In corrosive environments, the duckbill valve may consist of corrosion-resistant materials designed to withstand the effects of harsh chemicals. Other varieties are made to withstand extreme temperatures or high levels of pressure.
One of the primary advantages of the duckbill valve is its relatively simple design and easy installation. These valves contain few operating components, and require little maintenance. They operate automatically based on water pressure, without the need for complex equipment or manual activation. They are also relatively low in cost compared to other types of backflow prevention devices. In the event of damage or plumbing changes, these valves can easily be removed and replaced to keep the system operating effectively.
These valves must be carefully sized to match the diameter of each pipe to ensure they will function as intended. A duckbill valve that's too large for the pipe may not allow sufficient flow, while those that are too small may not be effective at preventing contamination. Compared to metal valves, a duckbill valve's rubber construction may leave it more vulnerable to damage and corrosion over time.