Journeyman Plumbers Exam Isometric Analysis and Math 4 — Questions and Answers
Question 1: A journeyman needs to find the travel for a 45-degree rolling offset. The true offset diagonal is 10 inches and the vertical rise is 7 inches. What is the travel?
- 12.21 inches (Correct answer)
- 17.00 inches
- 10.00 inches
- 7.07 inches
Correct answer: 12.21 inches
Travel = √(diagonal² + rise²) × 1.414 is incorrect; Travel = true offset × 1.414 = 10 × 1.414 ≈ 14.14 is one method, but with a combined true offset: √(10² + 7²) = √149 ≈ 12.21 inches is the true diagonal set, then multiply by 1.414 for travel.
Question 2: What is the primary purpose of an isometric drawing in plumbing?
- To show a 3D representation of a piping system on a 2D surface (Correct answer)
- To calculate pipe pressures
- To determine pipe sizing
- To show a top-down floor plan
Correct answer: To show a 3D representation of a piping system on a 2D surface
Isometric drawings allow plumbers to visualize and communicate 3D pipe routing using a standardized 2D projection.
Question 3: A plumber calculates the cut length of a pipe using the formula: cut length = center-to-center measurement minus two take-outs. If the center-to-center is 24 inches and each take-out is 1.5 inches, what is the cut length?
- 21 inches (Correct answer)
- 22.5 inches
- 27 inches
- 19.5 inches
Correct answer: 21 inches
Cut length = 24 − (2 × 1.5) = 24 − 3 = 21 inches.
Question 4: On an isometric drawing, all measurements along the three isometric axes are drawn:
- To true (actual) scale (Correct answer)
- Foreshortened to 82%
- Doubled
- At half scale
Correct answer: To true (actual) scale
One of the key advantages of isometric drawing is that measurements along the three axes are drawn to true (actual) scale.
Question 5: If a pipe offset using 45-degree elbows has a spread (run) of 10 inches, what is the set (rise/offset)?
- 10 inches (Correct answer)
- 14.14 inches
- 7.07 inches
- 5 inches
Correct answer: 10 inches
For a 45-degree offset, spread equals the set, so the set is also 10 inches.
Question 6: A plumber is reading an isometric drawing and sees two pipes crossing without a bump shown at the intersection. What does this indicate?
- The two pipes connect at that point (Correct answer)
- The pipes cross without connecting (one passes over or under)
- The drawing has an error
- The pipes are the same size
Correct answer: The two pipes connect at that point
In isometric plumbing drawings, when pipes cross without a bump (jog), they are connected; a bump indicates one pipe crosses over another without connection.
Question 7: What math constant is used to convert between the diagonal travel of a 45-degree offset and the set?
- 0.707 (to get set from travel) or 1.414 (to get travel from set) (Correct answer)
- 3.14159
- 1.732
- 2.000
Correct answer: 0.707 (to get set from travel) or 1.414 (to get travel from set)
For 45-degree offsets: set = travel × 0.707, or travel = set × 1.414; both constants derive from the sine/cosine of 45 degrees.
