Journeyman Plumber ExamDrainage, Waste, and Venting (DWV) SystemsMedium
A plumber is repairing a section of a 4-inch cast iron drainage pipe. The repair involves cutting out a damaged section and replacing it. What is the most common and acceptable method for joining new cast iron pipe to existing cast iron pipe in residential or commercial DWV systems today?
- AThreaded connections.
- BNo-hub couplings (shielded hubless couplings).
- CSolvent welding.
- DLead and oakum joints.
Show answer & explanationAnswer & explanation
Correct answer: B. No-hub couplings (shielded hubless couplings).
While lead and oakum joints were historically common, no-hub couplings (shielded hubless couplings) are the predominant and most convenient method for joining cast iron DWV pipe today, especially for repairs and new installations where speed and ease are important. Solvent welding is for plastic pipe, and threaded connections are rare for drainage.
Why the other options are wrong
- A. Threaded connections are typically used for smaller diameter steel or brass pipe, not common for cast iron drainage.
- C. Solvent welding is the joining method for PVC or ABS plastic pipe, not cast iron.
- D. Lead and oakum joints are traditional but labor-intensive and less common for new work or repairs today.
Cast Iron Pipe Joining Methods
Techniques used to connect sections of cast iron pipe in drainage, waste, and vent systems, varying in historical use and modern application.
- Lead and oakum: traditional, labor-intensive.
- No-hub couplings: modern, easy, widely used.
- Maintains integrity of the DWV system.
- Ensures leak-free connections.
Memory trick: Cast iron, strong and old, but new joints make it bold!