Massachusetts Plumbers Journeyman Practice Exam

What is the required minimum liquid seal for each fixture trap?

1. 1 inch

2. 1 ½ inches

3. 2 inches

4. 2 ½ inches

The correct answer is: 2 inches

The required minimum liquid seal for each fixture trap is 2 inches. This standard is based on plumbing codes, which ensure that a sufficient seal of water is maintained to prevent sewer gases from entering a building through the plumbing system. A liquid seal creates a barrier, trapping the gas while allowing wastewater to flow through. Having a seal of at least 2 inches provides enough water to maintain this barrier despite fluctuations caused by drainage flow, helping to minimize the potential for siphoning or evaporation, which could compromise the seal. Hence, a 2-inch liquid seal effectively ensures that the plumbing system functions safely and efficiently.