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NITC Master Plumber practice questions

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Question 1Plumbing Systems Design and Layout

When laying out a building drain, what is the minimum horizontal slope required for a 100 mm (4 in) diameter pipe?

  1. 1 in 25 (4%)
  2. 1 in 100 (1%) Correct answer.
  3. 1 in 200 (0.5%)
  4. 1 in 50 (2%)

Explanation

Standard plumbing codes require a minimum fall of 1 in 100 (approximately 1%, or 1/8 inch per foot) for drainage pipes of 100 mm (4 in) diameter and larger. Smaller pipes need steeper gradients because their wetted perimeter relative to flow depth is less efficient. Using a flatter slope risks solids settling and blockage.

Question 2Plumbing Systems Design and Layout

In a sanitary drainage system, what is the primary purpose of a vent pipe?

  1. To provide a secondary path for stormwater
  2. To equalize air pressure and protect trap seals Correct answer.
  3. To increase the velocity of wastewater flow
  4. To carry away sewer gases to the outdoors

Explanation

A vent allows air to enter the drainage system so that pressure in the pipe remains near atmospheric, preventing siphonage of trap seals as waste flows. While it also discharges gases above the roof, its functional role in protecting trap seals is the design driver. Venting does not increase flow velocity or handle stormwater.

Question 3Plumbing Systems Design and Layout

A horizontal branch serving a water closet must connect to a vertical stack. The design specifies a fitting whose branch joins its vertical barrel at 45 degrees. Which fitting arrangement meets this requirement?

  1. A double sanitary tee on the vertical stack
  2. A sanitary tee with the branch entering horizontally
  3. A reducing coupling with a sweep elbow
  4. A wye branch with a 45-degree bend, or a combination fitting Correct answer.

Explanation

A wye's branch meets its straight barrel at 45 degrees; an added 45-degree bend aligns the inlet with the horizontal branch. A combination fitting provides that arrangement in one fitting. Sanitary tees may be permitted for ordinary horizontal-to-vertical drainage, but they do not meet the specified 45-degree branch-junction design.

Question 4Plumbing Systems Design and Layout

What is the minimum required air gap between a fixture outlet and the flood-level rim of a receptor for a water closet with a flushometer valve?

  1. Two times the effective opening of the outlet Correct answer.
  2. Half the diameter of the drain
  3. One pipe diameter of the supply
  4. Equal to the trap seal depth

Explanation

An air gap must be at least twice the effective opening of the water supply outlet and never less than 25 mm (1 in) above the flood-level rim. This separation prevents backflow by providing an unobstructed physical break. The other values do not correspond to the standard air gap rule.

Question 5Plumbing Systems Design and Layout

A 15 mm (1/2 in) nominal copper tube supplies a group of fixtures with a total demand of 30 fixture units. What is the primary factor that determines the minimum pipe size?

  1. The pressure at the meter only
  2. The number of fixture units alone
  3. The developed length plus equivalent length of fittings, and the available pressure Correct answer.
  4. The diameter of the building drain

Explanation

Supply pipe sizing requires balancing available pressure against friction losses from developed length, equivalent fitting lengths, elevation changes, and fixture demand. Fixture units alone do not determine size because a short run with high pressure can use a smaller pipe than a long run with low pressure. The building drain diameter is unrelated to supply sizing.

Question 6Plumbing Systems Design and Layout

For a residential water heater installation, what is the purpose of a thermal expansion tank on a closed system?

  1. To store hot water for peak demand
  2. To absorb the volume increase as water is heated and prevent excessive pressure Correct answer.
  3. To provide a backup supply during outages
  4. To reduce the temperature of the hot water

Explanation

In a closed system with a backflow preventer or check valve, heated water cannot expand back into the main, so pressure rises. A thermal expansion tank contains a compressed air charge that absorbs the added volume and keeps system pressure within safe limits. It does not store hot water, provide backup supply, or cool the water.

Question 7Plumbing Systems Design and Layout

In a drainage layout, what does the term 'developed length' refer to?

  1. The straight-line distance between the two farthest fixtures
  2. The total length of pipe measured along the centerline, including fittings Correct answer.
  3. The vertical rise of the stack
  4. The length of the vent terminal above the roof

Explanation

Developed length is measured along the centerline of the piping run, including the equivalent lengths of fittings and valves. It is the value used in friction-loss calculations for both drainage and supply design. Straight-line distance, stack rise, and vent terminal height are separate quantities.

Question 8Plumbing Systems Design and Layout

A building has a 100 mm (4 in) building drain and a 100 mm (4 in) building sewer. What is the minimum required slope for the building sewer?

  1. 1 in 25 (4%)
  2. 1 in 50 (2%)
  3. 1 in 100 (1%) Correct answer.
  4. 1 in 200 (0.5%)

Explanation

Building sewers of 100 mm (4 in) diameter and larger must slope at not less than 1 in 100 (1%) unless a lower slope is specifically engineered and approved. The same minimum applies to the building drain. Steeper slopes are permitted but not required, and flatter slopes risk solids deposition.

Question 9Plumbing Systems Design and Layout

Which condition requires the installation of a backwater valve on a building drain?

  1. When fixtures are installed below the elevation of the next upstream manhole Correct answer.
  2. When the building has more than three stories
  3. When the water closet is a flushometer type
  4. When the building drain connects to a public sewer

Explanation

A backwater valve is required where drainage fixtures are below the elevation of the next upstream manhole or the public sewer, because a surcharge could otherwise cause sewage to back up into the building. Simple connection to a public sewer, building height, or fixture type alone does not trigger the requirement.

Question 10Plumbing Systems Design and Layout

What is the minimum trap seal depth required for a plumbing fixture trap?

  1. 25 mm (1 in)
  2. 100 mm (4 in)
  3. 50 mm (2 in) Correct answer.
  4. 75 mm (3 in)

Explanation

Fixture traps must maintain a water seal of not less than 50 mm (2 in) and not more than 100 mm (4 in) to resist sewer gas while remaining self-cleaning. A shallower seal evaporates or siphons too easily, and a deeper seal traps debris. The 50 mm minimum is the standard requirement.

Question 11Plumbing Systems Design and Layout

A horizontal branch drain serving a kitchen sink connects to a vertical stack. What fitting is generally required at the stack connection?

  1. A test tee
  2. A sanitary tee Correct answer.
  3. A double sanitary tee
  4. A wye branch with a 45-degree bend

Explanation

For a horizontal branch from a sink, a sanitary tee is acceptable at the vertical stack because the fixture does not discharge the heavy solids associated with water closets. The tee provides a smooth entry and adequate venting. Wye-and-bend fittings are reserved for water closet branches and other heavy-discharge fixtures.

Question 12Plumbing Systems Design and Layout

What is the primary function of a relief vent in a drainage system?

  1. To provide fresh air to a fixture trap
  2. To drain condensate from the vent system
  3. To terminate the vent above the roof
  4. To relieve pressure in a stack between the fixture branch and the stack vent Correct answer.

Explanation

A relief vent provides an additional path for air to enter the drainage stack between the fixture branch and the stack vent, reducing pressure fluctuations that could siphon traps. It is commonly used on stacks serving multiple floors. It does not supply fresh air to a single trap, drain condensate, or serve as the roof terminal.

Question 13Plumbing Systems Design and Layout

In a water distribution layout, which arrangement best prevents thermal siphoning between a hot and cold water line that share a common vertical run?

  1. Install a check valve on the cold line
  2. Separate the lines with an air gap
  3. Maintain a minimum horizontal separation and insulate the hot line Correct answer.
  4. Place the hot line above the cold line

Explanation

Thermal siphoning occurs when hot water circulates through a shared cold line due to density differences. Maintaining separation between hot and cold runs and insulating the hot pipe limits heat transfer. An air gap is not applicable to pressurized supply lines, and a check valve does not stop internal circulation within a shared run.

Question 14Plumbing Systems Design and Layout

What is the minimum size of a building vent stack that serves a 100 mm (4 in) drainage stack?

  1. 50 mm (2 in) Correct answer.
  2. 75 mm (3 in)
  3. 40 mm (1.5 in)
  4. 100 mm (4 in)

Explanation

A vent stack serving a 100 mm (4 in) drainage stack is generally required to be at least 50 mm (2 in) in diameter, though the exact size depends on the total fixture units and developed length per the sizing tables. It must never be smaller than the minimum allowed by the vent sizing table. A 40 mm vent is below the minimum for this stack size.

Question 15Plumbing Systems Design and Layout

Which fixture is required to be connected to a grease interceptor in a commercial kitchen layout?

  1. A dishwasher with a built-in grinder
  2. A mop sink
  3. A pre-rinse sink and a three-compartment sink Correct answer.
  4. A hand sink

Explanation

Grease-laden waste from pre-rinse sinks, three-compartment sinks, and similar food-preparation fixtures must pass through a grease interceptor before entering the drainage system. Hand sinks and mop sinks carry minimal grease and are typically exempt. Dishwashers may require separate treatment depending on local rules but are not the standard interceptor connection.

Question 16Plumbing Systems Design and Layout

What is the purpose of a circuit vent in a drainage layout?

  1. To vent a group of fixtures on a horizontal branch using a single vent Correct answer.
  2. To terminate the building drain
  3. To provide combustion air to a boiler
  4. To vent a single fixture trap

Explanation

A circuit vent allows a single vent to serve a group of fixtures connected to one horizontal branch, provided the branch is sized and arranged per code. It reduces the number of individual vents while protecting trap seals. It does not vent a single trap, supply combustion air, or terminate the building drain.

Question 17Plumbing Systems Design and Layout

A two-story building has a soil stack serving water closets on both floors. What is the minimum required size of the stack if the total fixture units exceed the capacity of a 75 mm (3 in) stack?

  1. 100 mm (4 in) Correct answer.
  2. 75 mm (3 in)
  3. 65 mm (2.5 in)
  4. 50 mm (2 in)

Explanation

When the total fixture units on a soil stack exceed the capacity of a 75 mm (3 in) stack, the next standard size, 100 mm (4 in), must be used. Stack sizing is based on fixture unit load and the number of branch intervals. A 50 mm or 65 mm stack is far too small for water closet service.

Question 18Plumbing Systems Design and Layout

In a pumped drainage system serving a basement fixture, what device prevents sewage from flowing back into the sump when the pump is off?

  1. A gate valve on the discharge line
  2. A check valve on the discharge line Correct answer.
  3. A vacuum breaker on the discharge line
  4. A relief valve on the discharge line

Explanation

A check valve on the discharge line of a sewage ejector pump closes when the pump stops, preventing backflow into the sump. A gate valve is for isolation only and does not prevent reverse flow. Vacuum breakers and relief valves address different concerns and do not stop backflow.

Question 19Plumbing Systems Design and Layout

What is the minimum required size of a vent terminal above the roof for a 50 mm (2 in) vent stack?

  1. 75 mm (3 in)
  2. 25 mm (1 in)
  3. 40 mm (1.5 in)
  4. 50 mm (2 in) Correct answer.

Explanation

A vent stack must extend through the roof at full size, so a 50 mm (2 in) vent stack requires a 50 mm (2 in) terminal. Reducing the terminal below the vent stack size would restrict airflow and is not permitted. The terminal must also extend the required distance above the roof surface.

Question 20Plumbing Systems Design and Layout

A horizontal wet vent is used to vent a bathroom group. Which condition must be met for the wet vent to be acceptable?

  1. The wet vent must be installed below the building drain
  2. The wet vent must be at least one pipe size larger than the drain it serves
  3. The wet vent must connect to a dry vent at its downstream end Correct answer.
  4. The wet vent may serve any number of fixtures regardless of load

Explanation

A horizontal wet vent carries waste from fixtures while also serving as the vent for other fixtures, and it must connect to a dry vent at its downstream end to maintain airflow. It is also limited in the fixture units it may serve and in the fixtures it may drain. It is not required to be larger than the drain, and it is not installed below the building drain.

Question 21Plumbing Systems Design and Layout

What is the primary reason for installing a trap primer on a floor drain?

  1. To prevent grease from entering the drain
  2. To maintain the water seal by replenishing evaporated water Correct answer.
  3. To increase the flow rate through the drain
  4. To provide a vent for the floor drain

Explanation

Floor drains that receive infrequent flow lose their trap seal through evaporation, allowing sewer gas to enter. A trap primer supplies a small amount of water periodically to maintain the seal. It does not increase flow, intercept grease, or vent the drain.

Question 22Plumbing Systems Design and Layout

In a multi-story building, what is the function of a yoke vent?

  1. To connect the vent stack to the soil stack at each floor to equalize pressure Correct answer.
  2. To provide combustion air to the water heater
  3. To terminate the vent above the roof
  4. To drain the vent stack of condensate

Explanation

A yoke vent connects the vent stack to the soil or waste stack at each floor level, equalizing pressure between the two and reducing the risk of trap siphonage. It is used where the vent stack and drainage stack are separate. It does not supply combustion air, drain condensate, or serve as the roof terminal.

Question 23Plumbing Systems Design and Layout

What is the minimum required clearance between a water closet and a side wall in a residential bathroom layout?

  1. 380 mm (15 in) Correct answer.
  2. 150 mm (6 in)
  3. 600 mm (24 in)
  4. 760 mm (30 in)

Explanation

A water closet must be installed with at least 380 mm (15 in) of clear space from its centerline to any side wall or partition. This clearance allows comfortable use and access for maintenance. Larger clearances are permitted but the minimum is 380 mm.

Question 24Plumbing Systems Design and Layout

A building's water service enters at 400 kPa (58 psi) and the highest fixture is 10 m above the meter. What is the approximate static pressure at the fixture, ignoring friction?

  1. Approximately 300 kPa (43 psi) Correct answer.
  2. Approximately 400 kPa (58 psi)
  3. Approximately 500 kPa (73 psi)
  4. Approximately 200 kPa (29 psi)

Explanation

Static pressure decreases by about 9.8 kPa per meter of elevation (0.433 psi per foot). A 10 m rise reduces pressure by roughly 98 kPa (14.2 psi), leaving about 300 kPa (43 psi). Friction losses would reduce it further, and the other values do not reflect the elevation loss.

Question 25Plumbing Systems Design and Layout

Which of the following is a required characteristic of a cleanout installed on a building drain?

  1. It must be installed at every change of direction greater than 45 degrees Correct answer.
  2. It must be installed only at the building sewer connection
  3. It must be installed at the highest point of the drain
  4. It must be concealed within a wall cavity

Explanation

Cleanouts are required at the building sewer connection, at the building drain, and at each change of direction greater than 45 degrees in horizontal drainage piping, among other locations. They must remain accessible, so concealing one in a wall cavity without an access panel is not acceptable. The highest point of the drain is not a cleanout location.

Question 26Plumbing Systems Design and Layout

In sizing a water distribution system for a building, what does the term 'fixture unit' represent when applying a demand load table?

  1. The probable peak flow demand a fixture imposes relative to a standard fixture Correct answer.
  2. The physical pipe length from the fixture to the nearest branch connection
  3. The actual volume of water a fixture draws during one full flush cycle
  4. The minimum static pressure needed for the fixture to operate correctly

Explanation

Fixture units are a dimensionless weighting that expresses the probable simultaneous demand of a fixture relative to a reference fixture, allowing dissimilar fixtures to be summed for pipe sizing. They are not a volume, a length, or a pressure value. The demand curve then converts the accumulated fixture units into an expected flow rate.

Question 27Plumbing Systems Design and Layout

A designer is laying out a water service pipe that will pass beneath a paved roadway on a site. Which installation practice best protects the service line in this location?

  1. Lay the pipe at a depth providing adequate cover for the expected traffic loading Correct answer.
  2. Install the line with a continuous upward slope back toward the public main
  3. Reduce the pipe diameter to limit the trench width and backfill volume
  4. Support the pipe on blocking at intervals with the trench left open

Explanation

Buried water service piping under vehicular traffic must be placed deep enough, or otherwise protected, so that the expected wheel loading is not transmitted to the pipe. Adequate cover and proper bedding distribute surface loads safely. Diameter, slope direction, and leaving trenches open do not address structural protection of the line.

Question 28Plumbing Systems Design and Layout

A horizontal soil pipe carries a water closet discharge and connects to a vertical stack. Which fitting arrangement is required at that connection to keep the flow from backing up into the branch?

  1. A vent tee with the branch entering above the stack flow line
  2. A double sanitary tee with both inlets on the same level
  3. A wye branch with a 45-degree bend directing flow downward into the stack Correct answer.
  4. A sanitary tee installed in the vertical stack at the branch connection

Explanation

Where a horizontal branch carrying a water closet discharge enters a vertical drainage stack, the connection must be made with fittings that turn the flow downward in the direction of stack flow, such as a wye and bend combination. A tee on its back or side can allow solids and water to deflect across the stack and back up the branch. The geometry of a wye with a bend guides the discharge smoothly downward.

Question 29Plumbing Systems Design and Layout

A drainage layout shows a horizontal branch with a change in direction of 90 degrees in a run serving a lavatory. How is the developed length of that branch measured for slope and sizing purposes?

  1. Along the centerline of the pipe including the fitting allowances at the bend Correct answer.
  2. As the straight-line horizontal distance between the two endpoints
  3. As the horizontal distance plus the vertical drop of the branch
  4. Along the inside wall of the pipe through the bend

Explanation

Developed length is measured along the centerline of the piping and includes the additional length contributed by fittings at changes in direction. Using only the straight-line distance ignores the extra run through the bend. Centerline measurement is the standard basis for applying slope and sizing rules.

Question 30Plumbing Systems Design and Layout

A designer must size a horizontal branch that serves several fixtures and connects to a stack where the branch also acts as a wet vent for fixtures on the same floor. Which principle governs the branch sizing in this arrangement?

  1. The branch size is set only by the largest fixture drain connected to it
  2. The branch may be sized on drainage load alone because the vent function is incidental
  3. The branch must be sized so the drainage load and the vented fixtures are both accommodated without exceeding the allowable load for its diameter Correct answer.
  4. The branch may be reduced one nominal size because wet venting improves air flow

Explanation

When a horizontal branch serves as a wet vent, it carries both drainage and venting duty, so its size must satisfy the drainage load limits for its diameter while remaining adequate for the fixtures it vents. Oversizing or undersizing without checking both functions can starve the vent or overload the drain. Sizing on drainage load alone, or on the largest fixture drain alone, ignores the dual role.

Question 31Water Supply and Distribution Systems

In a domestic cold-water supply system served directly by the public main, what is the primary purpose of installing a check valve on the service line at the meter outlet?

  1. To automatically drain the service line when the main is shut off
  2. To measure the volume of water consumed by the premises
  3. To reduce the pressure of water entering the building to a safe level
  4. To prevent backflow of water from the premises piping into the public main Correct answer.

Explanation

A check valve is a one-way device that allows flow into the premises but closes when flow reverses, protecting the public main from contamination by back-siphonage. Pressure reduction requires a pressure-reducing valve, drainage requires a drain valve, and consumption measurement requires a water meter, so those functions belong to different fittings.

Question 32Water Supply and Distribution Systems

A storage cistern supplies a cold-water distribution pipe serving several fixtures. Which arrangement best prevents contamination of the stored water?

  1. A submerged inlet with the outlet taken from the bottom of the cistern
  2. An inlet discharging above the highest possible water level with an air gap Correct answer.
  3. An inlet connected directly to the distribution pipe without any gap
  4. A sealed cistern pressurized by compressed air from the top

Explanation

Discharging the inlet above the maximum water level creates a physical air gap so that back-siphonage from the distribution pipe cannot reach the stored water. Submerged inlets or direct connections allow reverse flow to draw contamination into the cistern, which is why water bylaws require the air gap.

Question 33Water Supply and Distribution Systems

What is the standard nominal outside diameter of a copper tube designated as Type L, size 15 mm, in common plumbing practice?

  1. 22 mm
  2. 15 mm Correct answer.
  3. 12 mm
  4. 18 mm

Explanation

Metric copper tube is designated by its nominal outside diameter, and a 15 mm tube has an actual outside diameter of approximately 15 mm regardless of wall thickness. The type (K, L, M) changes the wall thickness and bore, not the nominal outside diameter.

Question 34Water Supply and Distribution Systems

A plumber is installing a cold-water branch and needs a fitting that allows a 90-degree change of direction with a swept, low-resistance flow path. Which fitting is most appropriate?

  1. A reducing bush
  2. A straight coupling
  3. A sanitary tee
  4. A 90-degree elbow Correct answer.

Explanation

A 90-degree elbow provides a compact right-angle change of direction on a pressure pipe run. A sanitary tee is a drainage fitting with a sweep for branch discharge, a coupling joins straight lengths, and a reducing bush adapts diameters, so none of those serves the same purpose on a supply branch.

Question 35Water Supply and Distribution Systems

Which property of water most directly explains why a distribution system must be designed to accommodate pressure surges when a valve is closed quickly?

  1. Water has a high specific heat capacity
  2. Water has a low viscosity
  3. Water is virtually incompressible Correct answer.
  4. Water has a high surface tension

Explanation

Because water is nearly incompressible, the kinetic energy of a moving column cannot be absorbed by compression when a valve closes abruptly, so it produces a pressure surge, commonly called water hammer. Designers allow for this by limiting velocities, using slow-closing valves, and installing surge arrestors.

Question 36Water Supply and Distribution Systems

What is the principal function of a pressure-reducing valve installed on the service pipe of a building connected to a high-pressure main?

  1. To remove suspended solids from the incoming water
  2. To maintain a reduced, stable downstream pressure regardless of upstream variations Correct answer.
  3. To prevent water from freezing in the service line
  4. To increase the flow rate at the furthest fixture

Explanation

A pressure-reducing valve throttles the incoming flow to hold a set downstream pressure even as the upstream main pressure fluctuates. This protects fixtures and fittings from excessive pressure while still delivering adequate flow. It does not boost flow, prevent freezing, or filter water.

Question 37Water Supply and Distribution Systems

Which material is generally preferred for underground cold-water service lines because it resists corrosion and is joined by heat fusion?

  1. Cast iron
  2. Galvanized steel
  3. Lead
  4. Polyethylene (PE) Correct answer.

Explanation

Polyethylene pipe is corrosion-resistant, flexible, and joined by heat fusion or mechanical compression fittings, making it well suited to buried cold-water service lines. Galvanized steel corrodes, cast iron is used mainly for drainage, and lead is prohibited for potable water.

Question 38Water Supply and Distribution Systems

A building's cold-water system is being designed with a storage cistern feeding a booster pump set. Which factor most directly determines the required capacity of the cistern?

  1. The length of the longest branch run only
  2. The diameter of the incoming service pipe only
  3. The number of fixtures and the daily demand they create Correct answer.
  4. The colour coding of the distribution pipework

Explanation

Cistern capacity is sized from the total daily demand, which depends on the number and type of fixtures served plus any fire or process allowance, and on the refill rate from the incoming main. Pipe diameter and run length affect hydraulics but do not by themselves set storage volume.

Question 39Water Supply and Distribution Systems

A cold-water branch supplies a group of fixtures with a total loading unit value of 30. Using a typical design chart, the branch is sized so that the velocity stays within accepted limits. What is the main reason for limiting velocity in the pipe?

  1. To keep noise and erosion within acceptable levels Correct answer.
  2. To increase the pressure at the fixtures
  3. To prevent the water from becoming corrosive
  4. To reduce the amount of pipe insulation required

Explanation

Excessive velocity produces noise, erosion-corrosion of pipe walls, and water hammer on valve closure, so design charts cap velocity. Lower velocity does not raise fixture pressure; it reduces friction loss, which is a side benefit of correct sizing rather than the controlling reason.

Question 40Water Supply and Distribution Systems

A plumber measures a static pressure of 300 kPa at the ground-floor tap of a building. What approximate static pressure would be expected at a tap 10 m higher in the same building, ignoring friction?

  1. Approximately 400 kPa
  2. Approximately 200 kPa Correct answer.
  3. Approximately 300 kPa
  4. Approximately 100 kPa

Explanation

Static pressure falls by about 10 kPa for every metre of rise, so a 10 m increase in height reduces pressure by roughly 100 kPa, giving about 200 kPa. Friction losses would reduce it further, so 200 kPa is an upper estimate.

Question 41Water Supply and Distribution Systems

A direct cold-water supply to a tall building cannot deliver adequate pressure to upper floors. Which solution is most appropriate?

  1. Reducing the number of taps on the ground floor
  2. Installing a cistern and booster pump set serving the upper floors Correct answer.
  3. Fitting a larger water meter at the boundary
  4. Increasing the diameter of the ground-floor branch only

Explanation

When the mains pressure is insufficient for the upper storeys, the standard approach is to break the supply into a storage cistern and pump the water to a high-level or rooftop tank, or to use a booster set. Enlarging pipework cannot create pressure that the main does not provide.

Question 42Water Supply and Distribution Systems

What is the minimum recommended air gap between the outlet of a warning pipe from a cistern and the flood level of the receiving surface, in a typical installation?

  1. Half the diameter of the warning pipe
  2. Twice the diameter of the warning pipe
  3. The diameter of the warning pipe, subject to a minimum Correct answer.
  4. No gap is required if the pipe discharges to a drain

Explanation

The warning pipe outlet must terminate with a visible air gap at least equal to the pipe diameter, and not less than a stated minimum, above the flood level of the receiving surface. This gap makes an overflow immediately visible and prevents back-siphonage into the cistern.

Question 43Water Supply and Distribution Systems

In a pumped cold-water distribution system, an accumulator vessel is installed on the discharge side of the pump. What is its main purpose?

  1. To store drinking water for emergency use
  2. To absorb pressure fluctuations and reduce pump cycling Correct answer.
  3. To measure the flow delivered by the pump
  4. To filter sediment from the pumped water

Explanation

An accumulator or pressure vessel contains a trapped air charge that compresses and expands, smoothing pressure surges and reducing the frequency of pump start-stop cycles. It does not store potable water for use, filter water, or meter flow.

Question 44Water Supply and Distribution Systems

A section of copper supply pipe is to be connected to a galvanized steel pipe. What precaution is most important at this joint?

  1. Increasing the pipe diameter at the transition
  2. Wrapping the joint in insulation to keep it warm
  3. Using a dielectric union to separate the dissimilar metals Correct answer.
  4. Soldering the steel directly to the copper with lead solder

Explanation

Copper and galvanized steel form a galvanic couple, and in the presence of water the less noble metal (the zinc coating on steel) corrodes rapidly. A dielectric union or isolating fitting breaks the electrical path and prevents this bimetallic corrosion.

Question 45Water Supply and Distribution Systems

Why is a loose-jointed or flexible coupling sometimes used in a long run of above-ground cold-water pipe?

  1. To reduce the noise of water flowing through the pipe
  2. To allow for thermal expansion and minor building movement Correct answer.
  3. To prevent the growth of bacteria in the pipe
  4. To increase the pressure rating of the pipeline

Explanation

Flexible couplings and expansion loops accommodate the dimensional changes caused by temperature variation and slight structural movement, preventing overstressing of joints. They do not raise the pressure rating, disinfect the water, or silence flow noise.

Question 46Water Supply and Distribution Systems

A plumber is testing a new cold-water installation with a pressure test. What is the usual purpose of maintaining the test pressure for a specified period?

  1. To reveal leaks or loss of pressure from defective joints Correct answer.
  2. To sterilize the pipework before use
  3. To calibrate the pressure gauge
  4. To allow the pipe to expand fully

Explanation

Holding the test pressure for a set period allows any leak or faulty joint to show up as a drop in pressure or visible escape of water. Sterilization is a separate chlorination procedure, and gauge calibration is not the purpose of the test.

Question 47Water Supply and Distribution Systems

A cold-water storage cistern is located in a roof space that may be subject to frost. Which measure best protects the stored water and the pipework?

  1. Increasing the cistern capacity to provide a thermal store
  2. Insulating the cistern and all exposed pipework, including the warning pipe Correct answer.
  3. Painting the cistern black to absorb heat
  4. Draining the cistern completely every winter

Explanation

Insulating the cistern body and lagging all exposed pipes, including the warning pipe, prevents freezing and protects the stored water. Draining the system each winter is impractical, and painting or enlarging the cistern does not prevent frost damage.

Question 48Water Supply and Distribution Systems

Which statement correctly describes the relationship between flow rate, pipe diameter, and velocity in a full-flowing cold-water pipe?

  1. For a given flow rate, velocity decreases as the pipe diameter decreases
  2. For a given flow rate, velocity is independent of pipe diameter
  3. For a given flow rate, velocity is proportional to the square of the diameter
  4. For a given flow rate, velocity increases as the pipe diameter decreases Correct answer.

Explanation

Velocity equals flow rate divided by cross-sectional area, and area falls with the square of the diameter. Reducing the diameter for the same flow therefore raises the velocity, which is why undersized branches cause noise and high friction loss.

Question 49Water Supply and Distribution Systems

A plumber observes that the pressure at a tap drops sharply whenever a nearby washing machine valve opens. Which explanation is most consistent with this observation?

  1. The pipe run to the tap has excessive friction loss and cannot sustain flow without a large pressure drop Correct answer.
  2. The static pressure in the system has permanently increased
  3. The water main has frozen solid
  4. The tap is fitted with an aerator that increases pressure

Explanation

When a second outlet draws flow, the velocity in the shared pipe rises and friction loss increases, so the pressure available at the tap falls. This points to an undersized or excessively long shared run rather than a change in static pressure.

Question 50Water Supply and Distribution Systems

A building uses a break tank and booster set to supply the upper floors, while the lower floors are fed directly from the main. Why is a break tank used rather than connecting the booster pump directly to the main?

  1. To increase the pressure available from the public main
  2. To avoid the need for any pressure test on the system
  3. To reduce the size of the distribution pipework
  4. To guarantee that pump suction cannot draw contaminants back into the public main Correct answer.

Explanation

A break tank creates a physical air gap between the public main and the pumped system, so a pump failure or surge cannot back-siphon water into the main. It is a backflow protection measure, not a pressure booster, and it does not remove the need for testing.