Master Plumber Exam Plumbing System Design & Sizing 4 — Questions and Answers
Question 1: Which of the following best describes the 'critical path' in a water distribution system design?
- The pipe with the highest pressure
- The longest or most restrictive path from source to the most remote fixture (Correct answer)
- The shortest route from the meter to the building
- The path carrying the most fixture units
Correct answer: The longest or most restrictive path from source to the most remote fixture
The critical path is the route with the greatest friction loss, used to size piping so the most remote or demanding fixture receives adequate pressure.
Question 2: A combination waste and vent system (CW&V) is permitted by IPC for which types of fixtures?
- Water closets and urinals only
- Floor drains, sinks, and lavatories in specific configurations (Correct answer)
- All fixtures above the second floor
- Only fixtures on the ground floor with direct access to the sewer
Correct answer: Floor drains, sinks, and lavatories in specific configurations
IPC Section 912 permits CW&V for floor drains, sinks, and lavatories where the system is designed with oversized horizontal drains acting as both drain and vent.
Question 3: What minimum residual pressure must be maintained at a flush valve water closet during peak demand per IPC?
- 8 psi
- 15 psi
- 25 psi (Correct answer)
- 40 psi
Correct answer: 25 psi
Flush valve water closets require a minimum residual pressure of 25 psi to operate properly, per IPC Table 604.3.
Question 4: When calculating the total demand in WSFU (water supply fixture units) for a system, what accounts for demand diversity?
- Adding all fixture units and multiplying by 1.5
- Using the probability curve that converts WSFU to gallons per minute (Correct answer)
- Applying a 25% safety factor to all pipe diameters
- Using the peak hour demand from the utility meter
Correct answer: Using the probability curve that converts WSFU to gallons per minute
Hunter's probability curve converts total WSFU to an estimated peak GPM, inherently accounting for the fact that not all fixtures operate simultaneously.
Question 5: An isometric drawing of a plumbing system is used primarily for what purpose?
- Showing the exterior elevation of the building
- Depicting a three-dimensional view of piping layout without true perspective (Correct answer)
- Calculating structural loads on floor joists
- Determining the number of fixtures per square foot
Correct answer: Depicting a three-dimensional view of piping layout without true perspective
An isometric diagram presents pipe runs in three dimensions on a 2D drawing, making it easier to visualize connections, slopes, and spatial relationships.
Question 6: Which sizing standard is used for gas piping design to ensure adequate BTU delivery to all appliances?
- Fixture unit method (Hunter's)
- Longest-length method or branch-length method per NFPA 54/IPC (Correct answer)
- Manning's roughness equation
- Hazen-Williams formula
Correct answer: Longest-length method or branch-length method per NFPA 54/IPC
NFPA 54 and IPC gas piping provisions use the longest-length or branch-length method to ensure pressure drop does not reduce BTU delivery below appliance requirements.
Question 7: What is the purpose of a 'check valve' in a plumbing system design?
- To regulate water pressure to 80 psi
- To allow flow in one direction only and prevent backflow (Correct answer)
- To provide thermal expansion relief
- To balance flow between parallel supply branches
Correct answer: To allow flow in one direction only and prevent backflow
A check valve permits flow in only one direction, preventing backflow that could contaminate supply water or damage equipment.
Master Plumber Exam Plumbing System Design & Sizing 4
Which of the following best describes the 'critical path' in a water distribution system design?