Master Plumber Exam Plumbing System Design 5 — Questions and Answers
Question 1: A sovent single-stack system eliminates conventional venting through the use of which key component?
- Air admittance valves at each fixture
- An aerator fitting at each story and a deaerator fitting at the base (Correct answer)
- A pressurized air injection system at the stack base
- A vacuum relief valve at the top of the stack
Correct answer: An aerator fitting at each story and a deaerator fitting at the base
The sovent system uses an aerator fitting at each floor connection to introduce air and prevent siphonage, and a deaerator at the base to separate air before it enters the building drain.
Question 2: In designing a recirculating hot water system for a large commercial building, the recirculation pump is sized to overcome which primary system resistance?
- The static head of the tallest riser in the building
- The friction losses through the longest circulation loop (Correct answer)
- The pressure differential between the water heater and the most distant fixture
- The velocity pressure of water flowing through the water heater
Correct answer: The friction losses through the longest circulation loop
The recirculation pump must overcome the friction head loss around the complete recirculation loop — the longer the loop, the greater the required pump head.
Question 3: Under the IPC, what is the maximum number of fixtures that may drain into a 3-inch horizontal branch drain at a 1/4-inch per foot slope?
- 6 drainage fixture units
- 20 drainage fixture units (Correct answer)
- 160 drainage fixture units
- 256 drainage fixture units
Correct answer: 20 drainage fixture units
A 3-inch horizontal branch at 1/4-inch per foot slope has a maximum capacity of 20 drainage fixture units per the IPC drainage sizing tables.
Question 4: When a plumbing system design includes a reduced-pressure zone (RPZ) backflow preventer, where must it be installed relative to the protected premises?
- Downstream of all fixtures it protects
- At the service entrance before any branch connections to the premises (Correct answer)
- After the water meter but before the pressure-reducing valve
- Inside a heated enclosure above the flood plain elevation
Correct answer: At the service entrance before any branch connections to the premises
An RPZ must be installed at the point of service entry before any branch connections to ensure complete protection of the downstream system.
Question 5: Which design approach is used to prevent thermal expansion pressure buildup in a closed hot water system that includes a backflow preventer on the cold supply?
- Increasing the water heater temperature relief valve setting
- Installing a thermal expansion tank on the cold water supply side (Correct answer)
- Reducing the system operating pressure below 60 psi
- Adding a pressure relief valve to the hot water return line
Correct answer: Installing a thermal expansion tank on the cold water supply side
A thermal expansion tank absorbs the increased volume of heated water, preventing dangerous pressure rise in a closed system that cannot expand back through the meter.
Question 6: In gravity-fed rainwater harvesting system design, collected rainwater used for toilet flushing must be treated to which standard before distribution?
- Drinking water (potable) standards per EPA
- Non-potable standards with turbidity below 2 NTU and coliform-free (Correct answer)
- No treatment is required if used only for flushing
- Industrial process water standards only
Correct answer: Non-potable standards with turbidity below 2 NTU and coliform-free
Most codes require harvested rainwater for toilet flushing to be filtered and disinfected to achieve less than 2 NTU turbidity and be free of coliform bacteria.
Question 7: What is the minimum required vent stack size when a drainage stack serves more than 10 branch intervals in a building?
- One-third the diameter of the drainage stack it serves
- One-half the diameter of the drainage stack it serves (Correct answer)
- Equal in diameter to the drainage stack it serves
- Two pipe sizes larger than the largest branch drain
Correct answer: One-half the diameter of the drainage stack it serves
Per IPC, the vent stack for a drainage stack serving more than 10 branch intervals must be at least one-half the diameter of the drainage stack.
Master Plumber Exam Plumbing System Design 5
A sovent single-stack system eliminates conventional venting through the use of which key component?