Free Journeyman Plumbers Water Supply and Distribution Questions and Answers — Questions and Answers
Question 1: A newly installed copper potable water distribution system in a commercial building must be tested for leaks. According to most model plumbing codes, what is the minimum required hydrostatic test pressure?
- 1.25 times the working pressure
- 100 psi or the working pressure, whichever is less
- 1.5 times the working pressure, but not less than 100 psi (Correct answer)
- Equal to the street main pressure
Correct answer: 1.5 times the working pressure, but not less than 100 psi
Most plumbing codes, including the International Plumbing Code (IPC) and Uniform Plumbing Code (UPC), require a hydrostatic test pressure of at least 1.5 times the system's working pressure. Additionally, there is often a minimum requirement, typically 100 psi, to ensure a thorough test even in low-pressure systems. This high pressure will reveal any leaks at joints or defects in the piping.
Question 2: In a residential hot water supply system with a backflow preventer or check valve installed at the source, what device is essential to protect the water heater and piping from excessive pressure due to thermal expansion?
- A pressure-reducing valve
- A water hammer arrestor
- A dielectric union
- A potable water expansion tank (Correct answer)
Correct answer: A potable water expansion tank
When water is heated, it expands. In a 'closed' system, created by a check valve or backflow preventer, this expansion creates a dangerous increase in pressure. A potable water expansion tank is designed with an air bladder to absorb this expanded water volume, keeping the system pressure within a safe range.
Question 3: A plumber is sizing a water service pipe for a single-family home using the Water Supply Fixture Unit (WSFU) method. The total WSFU load is 28, the developed length to the furthest fixture is 120 feet, and the static street pressure is 55 psi. Using a typical IPC/UPC sizing table, what is the minimum required size for the copper water service pipe?
- 3/4 inch
- 1 inch (Correct answer)
- 1 1/4 inch
- 1 1/2 inch
Correct answer: 1 inch
Based on typical plumbing code sizing tables (like those in the UPC or IPC), you would find the appropriate pressure range (e.g., 46-60 psi), then cross-reference the developed length column (e.g., 100-150 feet) with the WSFU load. For a load of 28 WSFU at that length and pressure, a 3/4" pipe is typically insufficient, making a 1-inch pipe the correct minimum size to maintain adequate pressure and flow.
Question 4: Which of the following locations would specifically require the installation of a water hammer arrestor according to most modern plumbing codes?
- At the connection to an outdoor hose bibb
- On the hot water supply line to a kitchen sink
- On the water supply lines for a clothes washing machine (Correct answer)
- At the highest point in the water distribution system
Correct answer: On the water supply lines for a clothes washing machine
Water hammer is caused by the sudden stoppage of water flow, creating a shockwave. Modern codes require water hammer arrestors to be installed near any quick-closing valves. The solenoid valves in a clothes washing machine are a prime example of quick-closing valves, making arrestors mandatory on both the hot and cold supply lines to prevent damage to the pipes.
Question 5: A plumber is performing a field test on a Reduced Pressure Principle (RP) backflow preventer (ASSE 1013). During the test of the relief valve, what is the minimum differential pressure at which the valve must begin to open and drip?
- 0.5 psid
- 5.0 psid
- 1.0 psid
- 2.0 psid (Correct answer)
Correct answer: 2.0 psid
According to the ASSE 1013 standard for Reduced Pressure Principle backflow prevention assemblies, the relief valve is a critical safety component. During a field test, it must open and begin to discharge water when the pressure differential between the check valves drops to 2.0 psid (pounds per square inch differential) or above. This ensures it will function correctly to prevent backflow.
Question 6: When installing a water service line, what is the general code requirement for the minimum horizontal separation distance between the potable water line and a sanitary sewer line in the same trench?
- The water line must be placed on a shelf 12 inches above the sewer line. (Correct answer)
- There is no minimum separation if the sewer pipe is cast iron.
- The pipes must be separated by at least 5 feet of undisturbed earth.
- A minimum of 18 inches is required, regardless of pipe material.
Correct answer: The water line must be placed on a shelf 12 inches above the sewer line.
To prevent contamination of the potable water supply in case of a leak, plumbing codes mandate specific separation requirements. The most common rule is that if the water line and sewer line are in the same trench, the water line must be placed on a solid shelf of earth at least 12 inches above the top of the sewer line. If they are at the same elevation, a much greater horizontal separation is required.
