waterseal

A water seal is a barrier formed by a standing column of water that blocks the passage of gases or vapors while allowing flow under controlled conditions. It relies on gravity and confinement to create a temporary, self-regulating barrier. Water seals are used in various engineering and medical devices to prevent backflow and to control ventilation.

In plumbing, water seals are most familiar in traps such as the U-shaped sections of piping called P-traps beneath sinks, bathtubs, and floor drains. The water contained in the trap forms a seal that blocks sewer gases from entering a building. The seal must be maintained by regularly supplying water; evaporation, leaks, or siphoning can break it. Proper venting and trap design help prevent siphon effects that might empty the seal.

In medical settings, water-seal chambers are used in chest drainage systems. A column of water provides a one-way barrier that allows air and fluid to escape from the body while preventing air from flowing back in. The system often includes a suction control and requires careful monitoring for bubbling, fluctuations, and fluid levels to assess drainage and detect leaks or blockages.

Water seals are also used in certain laboratory and industrial arrangements to prevent backflow while permitting venting or pressure equalization. Limitations include evaporation, mineral buildup, freezing in cold environments, and potential for blockage. Regular inspection and maintenance are required to keep a water seal functional.