Master Plumber Exam Gas Piping Systems 3 — Questions and Answers
Question 1: A sediment trap (drip leg) on a gas appliance connection must be installed:
- Upstream of the appliance shutoff valve
- Immediately upstream of the appliance inlet, after the shutoff valve (Correct answer)
- At the meter only
- Only on boilers, not furnaces
Correct answer: Immediately upstream of the appliance inlet, after the shutoff valve
The sediment trap must be located immediately upstream of the appliance to catch debris before it enters the appliance valve.
Question 2: Which gas pressure range is classified as 'intermediate pressure' under NFPA 54?
- 0.5 psi to 2 psi
- 2 psi to 5 psi (Correct answer)
- 5 psi to 125 psi
- Over 125 psi
Correct answer: 2 psi to 5 psi
Intermediate pressure gas systems operate between 2 psi and 5 psi according to NFPA 54 classifications.
Question 3: When a gas pipe passes through a concrete floor slab, it must be:
- Wrapped in PTFE tape
- Sleeved in a conduit sealed at both ends (Correct answer)
- Coated with joint compound
- Tested at double the normal pressure
Correct answer: Sleeved in a conduit sealed at both ends
Gas piping through concrete must be sleeved to protect the pipe from corrosion and allow for movement without cracking.
Question 4: What is the purpose of a pressure regulator on a gas system?
- To increase gas pressure for high-BTU appliances
- To reduce and maintain stable downstream gas pressure (Correct answer)
- To measure total gas consumption
- To filter contaminants from the gas supply
Correct answer: To reduce and maintain stable downstream gas pressure
A pressure regulator reduces higher upstream pressure to a stable, lower downstream pressure suitable for appliances.
Question 5: Under the International Fuel Gas Code, gas piping is NOT permitted to be run through which location?
- Exterior walls
- Concealed spaces in wood-frame walls
- Elevator shafts or dumbwaiter shafts (Correct answer)
- Crawl spaces
Correct answer: Elevator shafts or dumbwaiter shafts
Gas piping is prohibited in elevator shafts, dumbwaiter shafts, and similar enclosed shafts due to the severe fire and explosion risk.
Question 6: A master plumber is testing a new gas piping system with air before the gas is turned on. The test pressure must be held for a minimum of:
- 5 minutes
- 10 minutes (Correct answer)
- 15 minutes
- 30 minutes
Correct answer: 10 minutes
NFPA 54 requires the test pressure to be maintained for a minimum of 10 minutes with no measurable pressure drop.
Question 7: Which of the following best describes the specific gravity of natural gas compared to air?
- Natural gas is heavier than air and sinks to the floor
- Natural gas has the same density as air
- Natural gas is lighter than air and rises toward the ceiling (Correct answer)
- Natural gas density varies with outdoor temperature only
Correct answer: Natural gas is lighter than air and rises toward the ceiling
Natural gas (primarily methane) has a specific gravity of about 0.55, making it lighter than air, so it rises and dissipates upward.
Master Plumber Exam Gas Piping Systems 3
A sediment trap (drip leg) on a gas appliance connection must be installed: