Isometric Analysis and Math Flashcards
6 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 6 Isometric Analysis and Math flashcards as text
A plumber needs to install a 45-degree offset. The horizontal distance between the centerlines of the two parallel pipes, known as the 'set', is 20 inches. What is the center-to-center length of the 'travel' piece of pipe?
Answer: 28 1/4 inches
To find the travel for a 45-degree offset, you multiply the 'set' by the constant 1.414. In this case, 20 inches (set) x 1.414 = 28.28 inches. The closest fractional answer is 28 1/4 inches (28.25).
A horizontal drainage line that is 48 feet long must be installed with a uniform grade of 1/8 inch per foot. What is the total fall of the pipe from its starting point to its end point?
Answer: 6 inches
To calculate the total fall, multiply the length of the pipe run by the required grade per foot. Calculation: 48 feet * (1/8 inch/foot) = 6 inches.
When fabricating a rolling offset, a pipe must shift 15 inches horizontally (run) and 20 inches vertically (rise). What is the 'true offset' of this configuration?
Answer: 25 inches
The true offset of a rolling offset is the hypotenuse of the right triangle formed by the run and the rise. Using the Pythagorean theorem (a² + b² = c²), the calculation is 15² + 20² = c². This becomes 225 + 400 = 625. The square root of 625 is 25. Therefore, the true offset is 25 inches.
In pipe measurement, the dimension that must be subtracted from a center-to-center measurement to determine the exact cut length of the pipe is known as:
Answer: Fitting allowance
The fitting allowance, or take-off, is the length from the center of a fitting to the face of the fitting's socket or hub. This amount is subtracted from the center-to-center measurement for each fitting used to find the precise cut length of the pipe.
Which of the following is the correct mathematical constant used to calculate the 'travel' piece when the 'set' of a 60-degree offset is known?
Answer: 1.155
The constant for calculating the travel of a 60-degree offset is 1.155. The formula is: Travel = Set x 1.155. The constant 1.414 is for 45-degree offsets, and 2.613 is for 22.5-degree offsets.
An isometric drawing shows a vertical drain pipe rising from the floor. The line then turns to run horizontally toward the back and to the left. Which combination of fittings would be required to make this change of direction?
Answer: One 90-degree elbow and one 45-degree elbow
To change the pipe's direction from vertical to horizontal, a 90-degree elbow is needed. To then create the horizontal roll to the back and left, a 45-degree elbow is used in combination with the 90. This creates a three-dimensional change in direction that is common in plumbing systems.