Journeyman Plumbers Exam Isometric Analysis and Math 5 — Questions and Answers
Question 1: A sanitary drain must run 40 feet at a slope of 1/4 inch per foot. How much lower is the downstream end compared to the upstream end?
- 10 inches (Correct answer)
- 8 inches
- 5 inches
- 12 inches
Correct answer: 10 inches
Total drop = 40 feet × 0.25 inches/foot = 10 inches.
Question 2: When using 60-degree fittings to make an offset, the set constant (ratio of set to travel) is approximately:
- 0.866 (Correct answer)
- 0.707
- 0.500
- 1.000
Correct answer: 0.866
For a 60-degree offset, set = travel × 0.866 (the cosine of 30 degrees, since the fitting angle is 60 degrees).
Question 3: In isometric pipe drawing, how is a tee fitting typically shown when one branch comes toward the viewer?
- As a line branching along the front 30-degree axis toward the viewer (Correct answer)
- As a vertical line only
- As a horizontal line only
- It cannot be shown in isometric
Correct answer: As a line branching along the front 30-degree axis toward the viewer
In isometric drawing, branches are drawn along the appropriate isometric axis, including the front 30-degree axis for pipes coming toward the viewer.
Question 4: A plumber must offset a 3-inch pipe around a structural beam using two 45-degree elbows. The set required is 9 inches. What is the face-to-face pipe length between the two elbows?
- 12.73 inches minus the two elbow take-outs (Correct answer)
- 9.00 inches
- 12.73 inches plus the two elbow take-outs
- 9.00 inches minus the two elbow take-outs
Correct answer: 12.73 inches minus the two elbow take-outs
Travel = 9 × 1.414 = 12.73 inches total center-to-center; the cut pipe = 12.73 minus the take-outs of both elbows.
Question 5: Which formula correctly calculates the true length of a pipe in a rolling offset if the horizontal offset is H and the vertical rise is V?
- True offset = √(H² + V²), then travel = true offset × offset constant (Correct answer)
- Travel = H + V
- Travel = H × V
- Travel = √(H + V) × 1.414
Correct answer: True offset = √(H² + V²), then travel = true offset × offset constant
First find the true (diagonal) offset using the Pythagorean theorem: √(H² + V²), then multiply by the appropriate travel constant for the fitting angle.
Question 6: A plumber uses a pipe with an outside diameter of 4.5 inches and needs to determine the centerline radius when installing a 90-degree bend with a 1.5D radius. What is the centerline radius?
- 6.75 inches (Correct answer)
- 9.00 inches
- 4.50 inches
- 3.375 inches
Correct answer: 6.75 inches
Centerline radius = 1.5 × outside diameter = 1.5 × 4.5 = 6.75 inches.
Question 7: When converting an isometric pipe drawing to a bill of materials, which measurement is used to order pipe lengths?
- The cut (spool) length after subtracting fitting take-outs (Correct answer)
- The center-to-center measurement
- The face-to-face measurement of installed pipe
- The overall system length
Correct answer: The cut (spool) length after subtracting fitting take-outs
Pipe is ordered and cut to the spool (cut) length, which equals center-to-center minus the take-outs of both end fittings.
