Journeyman Plumbers Water Supply and Distribution Questions and Answers — Questions and Answers
Question 1: A newly installed potable water supply system within a commercial building must be tested for integrity. According to most plumbing codes, what is the minimum required hydrostatic test pressure?
- 100 psi for 15 minutes
- The system's working pressure for 2 hours
- 1.5 times the working pressure, but not less than 150 psi, for 2 hours (Correct answer)
- 50 psi for 4 hours
Correct answer: 1.5 times the working pressure, but not less than 150 psi, for 2 hours
Most plumbing codes, including the International Plumbing Code (IPC) and Uniform Plumbing Code (UPC), require that new potable water piping be tested at a pressure of at least 1.5 times the working pressure under which it is to be used. If the working pressure is unknown, a common standard is a minimum of 150 psi. The duration for this test is typically a minimum of 2 hours with no allowable leakage.
Question 2: A plumber is sizing the water distribution system for a single-family residence. The municipal water main provides a static pressure of 95 psi at the property line. Which of the following is required?
- A backflow preventer
- A pressure reducing valve (PRV) (Correct answer)
- A water hammer arrestor at the meter
- A larger diameter service pipe
Correct answer: A pressure reducing valve (PRV)
Most plumbing codes mandate that if the static water pressure from the street main is in excess of 80 psi, a pressure reducing valve (PRV) must be installed to protect the pipes, fixtures, and appliances within the building from damage. The PRV is typically set to maintain a pressure between 50 and 60 psi.
Question 3: To properly size a water supply system, a plumber uses the Water Supply Fixture Unit (WSFU) method. Which of the following best describes the principle behind this method?
- It calculates the peak water demand assuming all fixtures are used simultaneously.
- It assigns a weight to each fixture based on its water consumption, duration of use, and frequency of use to determine the probable peak demand. (Correct answer)
- It measures the static pressure required to operate the most demanding fixture in the system.
- It determines the pipe size based solely on the total number of fixtures in the building, regardless of type.
Correct answer: It assigns a weight to each fixture based on its water consumption, duration of use, and frequency of use to determine the probable peak demand.
The Water Supply Fixture Unit (WSFU) method, developed by Roy B. Hunter, is based on the theory of probability. It recognizes that not all fixtures will be used at the same time. Each fixture is assigned a WSFU value that represents its load-producing characteristics (water consumption, duration, and frequency of use), and these values are summed to estimate the peak probable demand on the system.
Question 4: In a multi-story building, how does an increase in elevation affect the available water pressure at the fixtures on the upper floors?
- Pressure increases by approximately 0.433 psi for every foot of elevation gain.
- Pressure is not affected by changes in elevation.
- Pressure decreases by approximately 0.433 psi for every foot of elevation gain. (Correct answer)
- Pressure decreases only if the pipe diameter is reduced.
Correct answer: Pressure decreases by approximately 0.433 psi for every foot of elevation gain.
Due to the weight of the column of water (hydrostatic head), for every foot of vertical rise in a water pipe, the pressure decreases by approximately 0.433 psi. This pressure loss due to elevation must be accounted for when designing a water distribution system to ensure adequate pressure at the highest fixtures.
Question 5: A plumber is installing water lines for a battery of washing machines in a laundromat. These machines have quick-closing solenoid valves. To prevent damage to the piping, which device is required?
- A check valve on each supply line
- An expansion tank
- A tempering valve
- Water hammer arrestors (Correct answer)
Correct answer: Water hammer arrestors
Fixtures with quick-closing valves, such as washing machines and dishwashers, can cause a sudden stop in water flow, creating a hydraulic shock wave known as water hammer. Plumbing codes require the installation of water hammer arrestors to absorb this shock and prevent damage to pipes, valves, and fixtures.
Question 6: What is the primary purpose of flushing a new potable water line before it is put into service?
- To test the system for leaks at maximum velocity.
- To remove any dirt, debris, or contaminants introduced during construction. (Correct answer)
- To pre-stretch the piping material before applying test pressure.
- To measure the maximum flow rate in gallons per minute (GPM).
Correct answer: To remove any dirt, debris, or contaminants introduced during construction.
Before a new water supply system is disinfected and tested, it must be thoroughly flushed with clean, potable water to remove any foreign materials, such as dirt, pipe shavings, excess flux, or other construction debris, that could contaminate the water or damage fixtures.
Journeyman Plumbers Water Supply and Distribution Questions and Answers
A newly installed potable water supply system within a commercial building must be tested for integrity.
According to most plumbing codes, what is the minimum required hydrostatic test pressure?