Journeyman Plumbers Exam Isometric Drawings and Analysis 5 — Questions and Answers
Question 1: An isometric drawing of a multi-story building shows a soil stack with horizontal branches at each floor. Which fitting at the base of the stack is critical and must be shown on the drawing?
- A reducing coupling
- A long-sweep 90° or combination wye and 1/8 bend at the stack base (Correct answer)
- A sanitary tee
- A P-trap
Correct answer: A long-sweep 90° or combination wye and 1/8 bend at the stack base
The base of a soil stack must transition to horizontal using a long-sweep 90° or combination wye and 1/8 bend to handle the high-velocity flow without blockage.
Question 2: When analyzing an isometric drawing, a plumber notices a wet vent serving multiple fixtures. Which fixture drain is typically permitted to serve as a wet vent under the IPC?
- The toilet (water closet)
- The lavatory or sink drain serving upstream fixtures (Correct answer)
- The kitchen sink drain only
- The floor drain
Correct answer: The lavatory or sink drain serving upstream fixtures
Under the IPC, a lavatory or sink drain that is properly sized can serve as a wet vent for upstream fixtures, carrying both waste and venting air.
Question 3: An isometric drawing shows a building drain sloped at 1/8" per foot instead of the standard 1/4" per foot. Under what condition is this permitted by the IPC?
- Never; 1/4" per foot is always required
- Only for pipe 3 inches and smaller
- For pipes 3 inches and larger where 1/4" slope is not achievable (Correct answer)
- Only for a maximum of 10 feet
Correct answer: For pipes 3 inches and larger where 1/4" slope is not achievable
The IPC permits 1/8" per foot minimum slope for building drains 3 inches and larger when structural conditions prevent the standard 1/4" slope.
Question 4: A plumber reviews an isometric drawing and finds a vent stack that does not connect back to the soil stack above the highest fixture. What code violation does this represent?
- The vent is too small in diameter
- The vent stack must reconnect (re-vent) to the soil stack at least 6 inches above the flood level rim of the highest fixture (Correct answer)
- The vent must be supported every 4 feet
- The vent must terminate at a cleanout
Correct answer: The vent stack must reconnect (re-vent) to the soil stack at least 6 inches above the flood level rim of the highest fixture
Vent stacks must reconnect to the soil or waste stack at a point at least 6 inches above the flood level rim of the highest fixture served to prevent sewer gas entry.
Question 5: When interpreting a complex isometric drawing, a plumber finds a circuit vent. How many fixtures can a single circuit vent typically serve under the IPC?
- 2 fixtures maximum
- 4 fixtures maximum
- 8 fixtures maximum (Correct answer)
- Unlimited, based on pipe size
Correct answer: 8 fixtures maximum
Under the IPC, a circuit vent may serve up to 8 fixtures connected to a horizontal branch drain.
Question 6: An isometric drawing shows an air admittance valve (AAV) terminating the vent on a kitchen sink island. What is the minimum height above the drain inlet an AAV must be installed?
- 2 inches
- 4 inches (Correct answer)
- 6 inches
- 12 inches
Correct answer: 4 inches
An AAV must be installed a minimum of 4 inches above the drain inlet it serves to function properly and prevent submersion.
Question 7: While analyzing an isometric drawing for a rough-in inspection, the plumber finds a drain pipe with a slope of 1/2" per foot. What problem does excessive slope typically cause?
- Increased chance of pipe corrosion
- Liquid runs ahead of solids, leaving solids behind to accumulate and cause clogs (Correct answer)
- Insufficient trap seal depth
- Reduced vent effectiveness
Correct answer: Liquid runs ahead of solids, leaving solids behind to accumulate and cause clogs
Excessive slope causes liquids to outrun solids in the pipe, leaving solids behind which accumulate and cause blockages over time.
