Journeyman Plumbers Drain, Waste, Vent Systems Questions and Answers — Questions and Answers
Question 1: What is the primary purpose of a vent in a drain, waste, and vent (DWV) system?
- To allow for the emergency drainage of stormwater.
- To provide a point of access for cleaning the drain lines.
- To regulate air pressure within the drainage system and prevent the siphoning of trap seals. (Correct answer)
- To filter out solid waste materials before they enter the main sewer line.
Correct answer: To regulate air pressure within the drainage system and prevent the siphoning of trap seals.
The primary purpose of a vent system is to regulate air pressure within the plumbing system. This allows drains to flow freely and prevents the vacuum effect that can siphon water out of fixture traps, which would otherwise allow sewer gases to enter the building.
Question 2: A plumber is installing a horizontal 3-inch PVC drain line that will carry waste from a bathroom group. According to most plumbing codes, what is the MINIMUM required slope for this pipe?
- 1/16 inch per foot
- 1/2 inch per foot
- 1/4 inch per foot
- 1/8 inch per foot (Correct answer)
Correct answer: 1/8 inch per foot
For horizontal drainage pipes between 3 and 6 inches in diameter, the standard minimum slope required by the International Plumbing Code (IPC) is 1/8 inch per foot. This ensures that solids are carried along with the liquids without the risk of stranding.
Question 3: Which of the following is an illegal and prohibited type of trap in a modern DWV system?
- P-trap
- S-trap (Correct answer)
- Drum trap
- Bottle trap
Correct answer: S-trap
S-traps are prohibited because they are prone to self-siphoning, where the velocity of the draining water can pull the trap seal along with it, leaving the trap empty and allowing sewer gas to enter the room. P-traps, when properly vented, prevent this issue.
Question 4: In a residential bathroom, a plumber connects the drain of a lavatory to the vertical drain of a toilet. This configuration, where the lavatory drain also serves as a vent for the toilet, is known as:
- A circuit vent
- An island fixture vent
- A wet vent (Correct answer)
- A crown vent
Correct answer: A wet vent
A wet vent is a pipe that functions as both a drain for one fixture and a vent for another. This is a common and code-compliant method used in bathroom groups to reduce the amount of vent piping required.
Question 5: According to the International Plumbing Code (IPC) and Uniform Plumbing Code (UPC), what is the acceptable range for a fixture trap's water seal depth?
- 1 inch to 3 inches
- 2 inches to 4 inches (Correct answer)
- 3 inches to 5 inches
- 4 inches to 6 inches
Correct answer: 2 inches to 4 inches
Plumbing codes specify that a standard trap seal must be between 2 and 4 inches deep. A seal less than 2 inches is susceptible to evaporation or being siphoned, while a seal deeper than 4 inches can slow drainage and lead to blockages.
Question 6: What is the minimum required length for a trap arm, as measured from the trap weir to the inner edge of the vent?
- One pipe diameter
- Two pipe diameters (Correct answer)
- Four pipe diameters
- There is no minimum length requirement.
Correct answer: Two pipe diameters
The trap arm must be at least two times the diameter of the pipe. This minimum distance prevents the vent from being installed too close to the trap, which would create a prohibited crown vent and could lead to the siphoning of the trap seal.
Journeyman Plumbers Drain, Waste, Vent Systems Questions and Answers
What is the primary purpose of a vent in a drain, waste, and vent (DWV) system?