DWV system layout, trap and vent requirements, and slope rules tested on plumbing licensing exams.
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- What does DWV stand for in plumbing?
- Drain, Waste, Vent - the system that removes used water and waste from buildings
- Name the three main components of a DWV system
- Drainage (pipes carrying waste), waste fixtures (sinks, toilets), and vent system (allows air circulation)
- What is a trap in a plumbing system?
- A U-shaped bend in a pipe that holds water to create a seal, blocking sewer gases from entering the building
- What is the most common trap type used in modern residential plumbing?
- P-trap (petcock trap) - resembles the letter P
- Why is the S-trap prohibited in most modern plumbing codes?
- It can self-siphon, causing the trap seal to be lost and allowing sewer gases to enter
- What is trap seal depth?
- The vertical distance of water standing in the trap bend, typically 2 to 4 inches
- What minimum trap seal depth is required by most plumbing codes?
- 2 inches
- Why is trap seal depth critical?
- If too shallow, water evaporates and the seal is lost; if too deep, it may discharge improperly
- What is the proper slope for horizontal drainage pipes?
- 1/4 inch per foot of pipe run (1 in 48 or approximately 2 percent grade)
- What is the maximum allowable slope for horizontal drainage pipes?
- 1/2 inch per foot (never more, as it can cause solids to settle improperly)
- What happens when a drainage pipe has insufficient slope?
- Wastewater flows too slowly, causing solids to accumulate and pipes to clog
- What is a trap arm in plumbing?
- The horizontal section of pipe between the trap outlet and the vent connection
- What is the maximum length of a trap arm before a vent is required?
- Generally 2 to 3 feet depending on pipe diameter and code, but varies by jurisdiction
- What is the purpose of cleanouts in a DWV system?
- To provide access for clearing blockages and inspecting the drainage system
- How far apart should cleanouts be spaced in horizontal runs?
- No more than 100 feet apart, or at every change of direction exceeding 45 degrees
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