Journeyman Plumber ExamDrainage, Waste, and Venting (DWV) SystemsMedium
A plumber is installing a fixture trap for a commercial floor drain in a restaurant kitchen. The drain is intended to receive discharge that may contain food particles and grease. What is the minimum required trap seal depth for this application?
- A2 inches
- B3 inches
- C1 inch
- D4 inches
Show answer & explanationAnswer & explanation
Correct answer: D. 4 inches
For commercial floor drains, especially in kitchens where evaporation or infrequent use might occur, plumbing codes typically require a minimum trap seal depth of 4 inches to provide a more robust barrier against sewer gases and accommodate potential evaporation or pressure fluctuations.
Why the other options are wrong
- A. 2 inches is a common minimum for residential lavatories or similar small fixtures, but not commercial floor drains.
- B. 3 inches is sometimes seen for water closets or certain larger residential fixtures, but still less than typically required for commercial floor drains.
- C. 1 inch is generally insufficient for any trap seal, as it's highly susceptible to evaporation and siphonage.
Commercial Floor Drain Trap Seal
The minimum vertical distance between the weir and the top of the dip of a trap, specifically for commercial floor drains, ensuring a sufficient water barrier against sewer gases.
- Prevents sewer gases from entering the building.
- Must be deep enough to resist evaporation and siphonage.
- Commercial applications often require deeper seals due to harsher conditions.
- Typically 4 inches for commercial floor drains.
Memory trick: Deep Seal, No Smell, All's Well.