Journeyman Plumbers Exam Isometric Drawings and Analysis 4 — Questions and Answers
Question 1: An isometric drawing shows a pipe transitioning from a 4-inch main to a 3-inch branch using a reducing fitting. What type of fitting is most likely shown?
- A bushing
- A reducing wye or tee (Correct answer)
- A coupling
- A union
Correct answer: A reducing wye or tee
A reducing wye or tee fitting is used to transition from a larger main to a smaller branch while maintaining proper flow direction in DWV systems.
Question 2: In an isometric drawing, a P-trap is shown with its outlet connecting to a horizontal drain pipe. What is the maximum distance the trap outlet can be from the vent under most US codes?
- 6 feet (Correct answer)
- 8 feet
- 10 feet
- 12 feet
Correct answer: 6 feet
Under most US plumbing codes, the trap-to-vent distance (trap arm length) for a P-trap must not exceed the distances in the code table, typically 6 feet for a 1.5" trap.
Question 3: When reviewing an isometric drawing of a water supply system, what symbol typically indicates a gate valve?
- A circle with an X
- Two triangles touching at their points with a line through them (Correct answer)
- A filled diamond
- A circle with a line through it
Correct answer: Two triangles touching at their points with a line through them
Gate valves are typically shown on isometric drawings as two triangles touching at their points (bow-tie shape) representing the wedge gate.
Question 4: An isometric drawing shows a hot water return line looping back to the water heater. What is the primary purpose of this loop as read from the drawing?
- To increase water pressure
- To maintain hot water temperature throughout the supply system (Correct answer)
- To act as a pressure relief route
- To serve as a recirculation loop for gray water
Correct answer: To maintain hot water temperature throughout the supply system
A hot water return line circulates water back to the heater to maintain temperature throughout the distribution system, eliminating long waits for hot water.
Question 5: On an isometric plumbing drawing, a double sanitary tee (back-to-back) is shown in a vertical stack. What is it primarily used for?
- Connecting horizontal drains at two levels
- Serving two back-to-back fixtures such as two bathrooms on opposite sides of a wall (Correct answer)
- Connecting a vent stack to a drain stack
- Creating a cleanout access point
Correct answer: Serving two back-to-back fixtures such as two bathrooms on opposite sides of a wall
A double sanitary tee installed in a vertical stack serves back-to-back fixtures on opposite sides of a wall, such as two bathroom groups.
Question 6: In an isometric drawing of a gas piping system, what does a union fitting allow the installer to do that a coupling does not?
- Increase flow capacity
- Disconnect piping without cutting or threading (Correct answer)
- Reduce the pipe size
- Change pipe material
Correct answer: Disconnect piping without cutting or threading
A union fitting has three parts that allow the piping to be disconnected and reconnected without cutting, which is essential for appliance servicing.
Question 7: An isometric drawing shows a backflow preventer on a domestic water service. What is its function?
- To boost water pressure to upper floors
- To prevent contaminated water from flowing back into the potable supply (Correct answer)
- To meter water usage
- To filter sediment from the supply
Correct answer: To prevent contaminated water from flowing back into the potable supply
A backflow preventer stops contaminated or non-potable water from reversing into the potable water supply due to back-pressure or back-siphonage.
