Which device is used to maintain a liquid seal and prevent sewer gas emissions?

The device used to maintain a liquid seal and prevent sewer gas emissions is the trap. Traps are plumbing fittings that stop gases from entering buildings while allowing for the passage of wastewater. They create a water seal, which acts as a barrier against sewer gases. This seal is formed by the water that remains in the curved section of the trap, thus preventing harmful gases from escaping into the living space.

On the other hand, vacuum breakers are designed to prevent backflow into the water supply, primarily protecting against contamination but do not maintain a liquid seal. Stack vents allow air to enter the drainage system to prevent vacuum conditions but also do not block sewer emissions directly. Water hammer arrestors are devices that temporarily absorb shock in the piping system caused by sudden changes in water flow, unrelated to preventing gas emissions.