Isometric Analysis and Math Flashcards
7 cards from real Journeyman Plumbers Exam practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Isometric Analysis and Math flashcards as text
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?
Answer: 10 inches
Total drop = 40 feet × 0.25 inches/foot = 10 inches.
When using 60-degree fittings to make an offset, the set constant (ratio of set to travel) is approximately:
Answer: 0.866
For a 60-degree offset, set = travel × 0.866 (the cosine of 30 degrees, since the fitting angle is 60 degrees).
In isometric pipe drawing, how is a tee fitting typically shown when one branch comes toward the viewer?
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.
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?
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.
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?
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.
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?
Answer: 6.75 inches
Centerline radius = 1.5 × outside diameter = 1.5 × 4.5 = 6.75 inches.
When converting an isometric pipe drawing to a bill of materials, which measurement is used to order pipe lengths?
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.