Master Plumber DWV and Storm Drainage Questions and Answers — Questions and Answers
Question 1: According to most plumbing codes, what is the minimum required air pressure and duration for testing a DWV (Drain, Waste, and Vent) system?
- 10 psi for 10 minutes
- 5 psi for 15 minutes (Correct answer)
- 15 psi for 5 minutes
- 5 psi for 30 minutes
Correct answer: 5 psi for 15 minutes
Standard plumbing codes, such as the IPC and UPC, typically require a DWV system to be tested with air at 5 psi for a duration of 15 minutes without any drop in pressure. This test ensures the system is airtight and free of leaks.
Question 2: A plumber is installing a horizontal drainage line for a series of sinks in a commercial building. The total developed length of the 4-inch pipe run is 120 feet. According to common plumbing codes, how many cleanouts are required for this section of piping?
- One at the end of the run
- One at the beginning and one at the end
- One at the beginning, one at the end, and one in the middle (Correct answer)
- One every 50 feet
Correct answer: One at the beginning, one at the end, and one in the middle
Most plumbing codes require a cleanout at the upper terminal of a horizontal drain and an additional cleanout for each 100 feet of developed length, or fraction thereof. Since the run is 120 feet, it requires a cleanout at the beginning, one for the first 100 feet, and another for the remaining 20 feet, which is often placed at the end of the run. Therefore, three cleanouts are necessary.
Question 3: Which of the following is an unacceptable practice when designing or installing a storm drainage system?
- Sizing conductors and leaders based on the maximum projected roof area and local rainfall rate.
- Discharging storm water onto a flat, graded area away from the building on a residential property.
- Connecting the primary roof drain system directly to the sanitary sewer system. (Correct answer)
- Providing a separate, independent secondary (overflow) drain system.
Correct answer: Connecting the primary roof drain system directly to the sanitary sewer system.
It is a fundamental plumbing principle and a strict code requirement that storm water drainage systems must be kept separate from sanitary sewer systems. Combining them can overwhelm sewage treatment facilities during heavy rainfall, leading to untreated sewage discharges.
Question 4: In a DWV system, what is the primary purpose of a vent?
- To provide a secondary path for waste in case of a clog.
- To filter out sewer gases before they enter the building.
- To equalize air pressure within the drainage system, protecting fixture trap seals from siphonage and back pressure. (Correct answer)
- To increase the velocity of waste flowing through the pipes.
Correct answer: To equalize air pressure within the drainage system, protecting fixture trap seals from siphonage and back pressure.
The vent system is crucial for maintaining neutral air pressure in the drainage pipes. As water flows down a drain, it can create negative pressure (siphonage) that pulls water from fixture traps, or positive pressure (back pressure) that pushes sewer gas through the trap. Vents allow air to enter and exit the system, preventing these issues and ensuring smooth drainage.
Question 5: A master plumber is overseeing the installation of an under-floor cleanout in a crawl space with limited access. According to the Uniform Plumbing Code (UPC), what is the maximum distance the cleanout can be from an access door or crawl hole?
- 20 feet
- 15 feet
- 10 feet
- 5 feet (Correct answer)
Correct answer: 5 feet
The Uniform Plumbing Code (UPC) specifies that an under-floor cleanout shall not be located more than 5 feet from an access door, trap door, or crawl hole to ensure it is readily accessible for maintenance and rodding.
Question 6: When sizing a vertical storm drain conductor for a large commercial building, which of the following factors is most critical?
- The number of plumbing fixtures in the building.
- The total length of the horizontal storm drain.
- The maximum projected roof area and the local hourly rainfall rate. (Correct answer)
- The material of the DWV piping.
Correct answer: The maximum projected roof area and the local hourly rainfall rate.
The size of vertical conductors, leaders, and horizontal storm drains is determined by the amount of water they must carry. This is calculated based on the size of the surface area collecting rain (the projected roof area) and the intensity of the rainfall in that specific geographic location (rainfall rate).
Master Plumber DWV and Storm Drainage Questions and Answers
According to most plumbing codes, what is the minimum required air pressure and duration for testing a DWV (Drain, Waste, and Vent) system?