Journeyman Plumbers Exam Isometric Drawings and Analysis 3 — Questions and Answers
Question 1: Using an isometric drawing, a plumber measures a pipe run as 6 isometric inches long at 30°. What is the true horizontal length of that pipe?
- 6 inches (Correct answer)
- 5.2 inches
- 3 inches
- 12 inches
Correct answer: 6 inches
On a properly scaled isometric drawing, dimensions along the isometric axes represent true lengths, so 6 isometric inches equals 6 actual inches.
Question 2: A plumber needs to calculate a 45° offset using an isometric drawing. If the offset travel is 12 inches, what is the approximate run?
- 12 inches
- 8.5 inches (Correct answer)
- 17 inches
- 24 inches
Correct answer: 8.5 inches
For a 45° offset, the run equals the offset travel multiplied by 0.707, so 12 × 0.707 ≈ 8.5 inches.
Question 3: An isometric drawing shows a horizontal drain with a 1/4" per foot slope over a 20-foot run. What is the total drop?
- 5 inches (Correct answer)
- 20 inches
- 2.5 inches
- 10 inches
Correct answer: 5 inches
Total drop = 1/4" × 20 = 5 inches over the 20-foot horizontal run.
Question 4: When analyzing an isometric drawing for a parallel offset, which multiplier is used to find the diagonal travel for a 22.5° offset?
- 1.082
- 1.414
- 2.613 (Correct answer)
- 1.307
Correct answer: 2.613
For a 22.5° offset, the travel multiplier is 2.613, applied to the offset distance to find the fitting-to-fitting diagonal length.
Question 5: An isometric drawing shows a 60° offset on a 3-inch pipe. If the set (offset distance) is 9 inches, what is the approximate travel?
- 10.4 inches (Correct answer)
- 7.8 inches
- 18 inches
- 12.7 inches
Correct answer: 10.4 inches
For a 60° offset, travel = set ÷ sin(60°) = 9 ÷ 0.866 ≈ 10.4 inches.
Question 6: When reading an isometric drawing, a plumber sees two parallel pipes that must be offset around the same obstruction. What must be calculated for each pipe separately?
- Only the travel
- Both the travel and the spread between the offsets (Correct answer)
- Only the set distance
- Only the pipe diameter
Correct answer: Both the travel and the spread between the offsets
For parallel offsets, each pipe needs its own travel calculated, and the spread (center-to-center distance) must account for fitting dimensions.
Question 7: On an isometric drawing, a sanitary cross is shown connecting four pipe ends. In which application is a sanitary cross generally NOT permitted in DWV systems under most plumbing codes?
- In a horizontal-to-horizontal connection (Correct answer)
- In a vertical stack connection
- As a test tee fitting
- In a roof drain connection
Correct answer: In a horizontal-to-horizontal connection
Sanitary crosses are generally not permitted for horizontal branch connections because they can allow back-siphonage between opposing branches.
