Master Plumber Water Supply and Distribution Questions and Answers — Questions and Answers
Question 1: A new potable water system has been installed in a commercial building. According to the IPC, which of the following is an acceptable method for disinfection before the system is put into service?
- Flushing the system with hot water at 140°F for at least 30 minutes.
- Filling the system with a solution containing at least 25 ppm of chlorine and letting it stand for 12 hours.
- Flushing the system thoroughly with clean, potable water until all visible debris is removed.
- Filling the system with a solution containing at least 50 ppm of chlorine and letting it stand for 24 hours. (Correct answer)
Correct answer: Filling the system with a solution containing at least 50 ppm of chlorine and letting it stand for 24 hours.
The International Plumbing Code (IPC) Section 610 outlines the requirements for disinfecting a potable water system. An approved method involves filling the system with a water/chlorine solution of at least 50 parts per million (ppm) and allowing it to stand for 24 hours. Alternatively, a solution of at least 200 ppm can be used for a 3-hour period.
Question 2: A master plumber is designing a water supply system for a multi-story building. The static pressure from the municipal water main is 95 psi. What is required on the water service pipe near its entrance to the building?
- A water hammer arrestor
- A pressure-reducing valve (PRV) (Correct answer)
- A thermal expansion tank
- A backflow preventer
Correct answer: A pressure-reducing valve (PRV)
Most plumbing codes, including the IPC, require a pressure-reducing valve (PRV) to be installed when the static water pressure exceeds 80 psi. This is to protect fixtures and appliances from damage caused by excessive pressure.
Question 3: In a residential hot water supply system, a check valve has been installed on the main water service, creating a closed system. Which of the following is required to mitigate the effects of thermal expansion?
- An additional pressure relief valve set at 100 psi.
- A larger diameter cold water supply pipe to the water heater.
- An approved and adequately sized expansion tank. (Correct answer)
- A circulation pump installed on the hot water line.
Correct answer: An approved and adequately sized expansion tank.
When a backflow preventer, check valve, or pressure-reducing valve creates a closed system, thermal expansion of heated water can cause a dangerous increase in pressure. Plumbing codes mandate that an approved expansion tank or other device designed for thermal expansion control must be installed to absorb this increased volume and pressure.
Question 4: A master plumber needs to determine the required size for a water service pipe for a new office building. The calculation involves determining the total water supply fixture units (WSFU), the developed length of the piping, and pressure losses. What additional piece of information is critical for this calculation?
- The type of insulation on the hot water pipes.
- The number of floors in the building.
- The available static water pressure at the source. (Correct answer)
- The average daily temperature of the supply water.
Correct answer: The available static water pressure at the source.
To properly size a water service pipe, you must know the starting pressure available from the municipal main or other source. This initial pressure is a key factor in calculating whether sufficient pressure will be available at the most remote fixture after accounting for all pressure losses due to friction, elevation, and equipment.
Question 5: Which of the following scenarios explicitly requires the installation of a water hammer arrestor according to the IPC?
- On any water supply line exceeding 100 feet in developed length.
- At the base of every water supply riser in a multi-story building.
- On the water supply lines to fixtures with quick-closing valves. (Correct answer)
- Immediately downstream of the main water meter for the building.
Correct answer: On the water supply lines to fixtures with quick-closing valves.
The IPC Section 604.9 states that a water hammer arrestor shall be installed where quick-closing valves are used. These valves, such as those on clothes washers and dishwashers, can stop the flow of water abruptly, causing a hydraulic shock (water hammer) that can damage pipes and fixtures. The arrestor absorbs this shock.
Question 6: When calculating the total pressure loss in a water distribution system, a master plumber accounts for losses from pipe friction, elevation changes, and the water meter. What other significant source of pressure loss must be included for an accurate design?
- Pressure loss through fittings and valves. (Correct answer)
- The velocity of the water in the public main.
- The ambient temperature surrounding the pipes.
- The age of the municipal water supply infrastructure.
Correct answer: Pressure loss through fittings and valves.
Fittings (like elbows and tees) and valves create turbulence and friction, resulting in pressure loss. This loss is often accounted for by using the concept of 'equivalent length,' where each fitting is assigned a value equal to the pressure loss of a certain length of straight pipe. Failing to include these losses can lead to undersized pipes and insufficient pressure at fixtures.
Master Plumber Water Supply and Distribution Questions and Answers
A new potable water system has been installed in a commercial building.
According to the IPC, which of the following is an acceptable method for disinfection before the system is put into service?