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PGDB Certifying Plumber practice questions

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Question 1Sanitary plumbing and drainage systems

Under a conventional gravity sanitary drainage system, what is the primary purpose of the vent pipe connected to a fixture drain?

  1. To drain condensate from the water heater relief line
  2. To carry greywater from the fixture to the sewer connection
  3. To supply pressurised water for flushing fixtures
  4. To equalise air pressure in the drain and protect fixture trap seals from siphonage Correct answer.

Explanation

A vent admits air to the drainage system so that pressure differences caused by flowing water are equalised. This protects the water seal in each fixture trap from being siphoned out or blown back, which would allow sewer gas into the building.

Question 2Sanitary plumbing and drainage systems

A water closet trap seal must maintain a minimum depth to resist sewer gas entry. What is the standard minimum trap seal depth for sanitary fixtures?

  1. 50 mm Correct answer.
  2. 150 mm
  3. 100 mm
  4. 25 mm

Explanation

Plumbing codes generally require a minimum water seal of 50 mm in each fixture trap. A deeper seal is acceptable up to the code maximum, but 50 mm is the recognised minimum for effective gas retention.

Question 3Sanitary plumbing and drainage systems

When installing a horizontal drainage branch, why must a uniform fall be maintained along its length?

  1. To keep the pipe above the frost line only
  2. To maintain self-cleansing velocity and prevent solids from settling Correct answer.
  3. To allow the pipe to double as a vent path
  4. To reduce the volume of water needed to flush fixtures

Explanation

Gravity drainage relies on a consistent gradient to move solids along with the liquid. Correct fall produces self-cleansing velocity, so solids do not settle and cause blockages, while excessive fall can leave liquids behind.

Question 4Sanitary plumbing and drainage systems

A backflow prevention device is required on a hose tap used to fill a bucket in a commercial kitchen. What hazard does this device primarily address?

  1. Scale build-up inside the tap body
  2. Freezing of the supply line in winter
  3. Cross-connection allowing contaminants to be drawn back into the potable supply Correct answer.
  4. Excessive water pressure damaging the tap

Explanation

A hose tap can be submerged in a contaminated container, creating a cross-connection. A backflow prevention device stops contaminated water being siphoned back into the drinking water supply during a pressure drop.

Question 5Sanitary plumbing and drainage systems

Which fixture is required to be connected to the sanitary drainage system through a trap that is separate from other fixtures?

  1. A hand basin in a public amenity
  2. A drinking fountain
  3. A water closet pan Correct answer.
  4. A floor waste gully serving a shower area

Explanation

Each fixture must have its own trap, and a water closet must not share a trap with another fixture. Shared traps risk cross-contamination and siphonage between fixtures, so individual trapping is required.

Question 6Sanitary plumbing and drainage systems

What is the function of an inspection opening (IO) installed at the base of a drainage stack?

  1. To support the weight of the stack above
  2. To vent sewer gas to the atmosphere
  3. To provide access for clearing blockages and testing the drain Correct answer.
  4. To measure flow rate in the stack

Explanation

Inspection openings give maintenance access to the drainage system for rodding, clearing blockages, and pressure testing. They are placed at changes of direction and at the base of stacks where blockages commonly occur.

Question 7Sanitary plumbing and drainage systems

A discharge pipe from a domestic dishwasher must be connected to the drainage system in a way that prevents backflow. Which arrangement is acceptable?

  1. Directly connected to the sewer with no air break
  2. Discharging through an air gap or high loop before the trap connection Correct answer.
  3. Discharging onto the floor without any connection
  4. Connected to the toilet cistern inlet

Explanation

Dishwasher discharge must be protected against backflow by an air gap or a high loop arrangement before entering the drainage system. This prevents dirty water from siphoning back and contaminating the appliance or potable supply.

Question 8Sanitary plumbing and drainage systems

Which term describes the vertical pipe that carries soil and waste from upper floors down to the building drain?

  1. Building sewer
  2. Soil and waste stack Correct answer.
  3. Branch drain
  4. Relief vent

Explanation

The soil and waste stack is the vertical drainage pipe that conveys discharge from fixtures on upper levels to the building drain. Branch drains connect fixtures to the stack, and the building sewer carries flow from the drain to the public sewer.

Question 9Sanitary plumbing and drainage systems

A 100 mm diameter horizontal drainage pipe runs at a gradient of 1 in 60. Over a 12 m run, what is the total fall?

  1. 120 mm
  2. 240 mm
  3. 600 mm
  4. 200 mm Correct answer.

Explanation

Fall equals run divided by the gradient ratio: 12 m ÷ 60 = 0.2 m, or 200 mm. This confirms the pipe drops 200 mm over the 12 m length at a 1 in 60 gradient.

Question 10Sanitary plumbing and drainage systems

In a multi-storey building, a vent stack is installed alongside the soil stack. What is the main reason for providing this dedicated vent stack?

  1. To supply air for combustion appliances
  2. To provide a second path for stormwater drainage
  3. To relieve pressure differences along the soil stack and protect trap seals Correct answer.
  4. To carry wastewater in parallel with the soil stack

Explanation

A vent stack runs the height of the drainage stack to equalise air pressure and prevent trap seal loss from siphonage or back pressure. It carries air only and is essential in tall buildings where pressure fluctuations are significant.

Question 11Sanitary plumbing and drainage systems

A fixture trap in a rarely used guest bathroom has lost its water seal. Which cause is most likely?

  1. Oversized branch drain diameter
  2. Evaporation of the trap seal over time Correct answer.
  3. Excessive venting of the fixture
  4. Incorrect pipe gradient in the branch

Explanation

Traps in fixtures that are not used regularly lose their seal through evaporation. The remedy is to run the fixture periodically or install a trap primer where the fixture cannot be regularly used.

Question 12Sanitary plumbing and drainage systems

During a drainage system test, water is held in the system to check for leaks. What is this test commonly called?

  1. Air pressure test
  2. Smoke test
  3. Dye test
  4. Hydrostatic test Correct answer.

Explanation

A hydrostatic test fills the drainage system with water and holds it under pressure to reveal leaks. Smoke and air tests are used to check for gas leaks or vent integrity, while dye tests trace connections.

Question 13Sanitary plumbing and drainage systems

A floor waste gully is installed in a wet area. What is the primary function of the gully riser and its surrounding grate?

  1. To collect surface water and direct it to the drainage system while retaining a trap seal Correct answer.
  2. To vent the drainage system to the room
  3. To increase the flow rate of the fixture branch
  4. To provide a decorative finish to the floor

Explanation

A floor waste gully collects surface water from the floor and delivers it to the drainage system. It incorporates a trap to retain a water seal and prevent sewer gas entering the wet area.

Question 14Sanitary plumbing and drainage systems

When connecting a new fixture branch to an existing soil stack, which fitting should be used to ensure smooth flow and avoid blockage?

  1. A flexible rubber sleeve
  2. A 90-degree tee with the branch entering at right angles
  3. A swept junction fitting with the branch entering in the direction of flow Correct answer.
  4. A straight coupling with a reducer

Explanation

A swept junction directs the branch flow in the direction of the stack flow, reducing turbulence and the chance of solids catching. A sharp right-angle tee creates a ledge where solids can accumulate.

Question 15Sanitary plumbing and drainage systems

Why is it important that a vent pipe terminates above the roof line and away from windows and air intakes?

  1. To allow rainwater to enter the vent for cleaning
  2. To increase the water pressure in the drainage system
  3. To reduce the noise of the drainage system
  4. To prevent sewer gases from entering the building and to allow proper air flow Correct answer.

Explanation

The vent must terminate outdoors above the roof so sewer gases discharge safely away from openings. Correct termination height and location prevent gases re-entering the building through windows or air intakes.

Question 16Sanitary plumbing and drainage systems

A plumbing system uses an air admittance valve (AAV) instead of a traditional vent. What limitation should the plumber consider?

  1. AAVs admit air but do not allow sewer gas to escape, so they must be installed in a ventilated space Correct answer.
  2. AAVs must be installed above the roof line
  3. AAVs increase water pressure in the drainage system
  4. AAVs cannot be used in any building

Explanation

An air admittance valve opens to admit air when pressure drops but closes to prevent sewer gas escaping. It must be located in a ventilated space and within the manufacturer's and code limits, and cannot replace every venting requirement.

Question 17Sanitary plumbing and drainage systems

A drainage pipe passes through a concrete slab. What is the purpose of installing a sleeve around the pipe at the penetration?

  1. To increase the flow capacity of the pipe
  2. To allow for movement and protect the pipe from damage Correct answer.
  3. To provide a vent path through the slab
  4. To prevent water from entering the pipe

Explanation

A sleeve at a slab penetration allows for thermal and structural movement and protects the pipe from abrasion or shear at the concrete edge. It also simplifies sealing and fire-stopping around the penetration.

Question 18Sanitary plumbing and drainage systems

Which condition is most likely to cause a drainage system to experience back pressure and blow trap seals?

  1. A correctly sized vent stack
  2. A partially blocked vent pipe Correct answer.
  3. A branch drain with a 1 in 40 gradient
  4. A trap with a 75 mm seal

Explanation

A blocked vent prevents air from entering the system, so flowing water creates negative or positive pressure that can siphon or blow trap seals. Correct venting and adequate trap depth protect against this.

Question 19Sanitary plumbing and drainage systems

What is the purpose of a reflux valve in a sanitary drainage system?

  1. To prevent reverse flow of sewage back into the building Correct answer.
  2. To measure the volume of wastewater discharged
  3. To vent the drain to the atmosphere
  4. To increase the velocity of flow in the drain

Explanation

A reflux valve allows flow in one direction only, preventing sewage from backing up into the building during surcharge or flooding of the public sewer. It is especially important where fixtures are below the flood level of the sewer.

Question 20Sanitary plumbing and drainage systems

A new sanitary drainage system is being designed for a building with fixtures on the ground floor and a basement. Why should the basement fixtures be protected by a pumped system or reflux valve?

  1. Because basement drainage cannot be vented
  2. Because basement fixtures require larger traps
  3. Because basement pipes must be smaller in diameter
  4. Because basement fixtures are below the flood level of the public sewer Correct answer.

Explanation

Fixtures below the flood level of the public sewer are at risk of sewage backing up into the building. A pumped system or reflux valve protects them from surcharge and prevents contamination of the basement.

Question 21Sanitary plumbing and drainage systems

In a combined drainage system, stormwater and sewage are carried in separate pipes until they reach the public sewer. Why is it important to keep the systems separate within the building?

  1. To increase the water pressure in the sewage pipes
  2. To reduce the number of vent pipes required
  3. To allow sewage to be used for irrigation
  4. To prevent stormwater from overloading the sewage treatment system and to avoid contamination Correct answer.

Explanation

Keeping stormwater separate from sewage prevents large storm flows from overloading the sewage system and treatment works. It also avoids contamination of stormwater and reduces the risk of sewage backing up into the building.

Question 22Sanitary plumbing and drainage systems

A plumber is installing a new toilet in a bathroom and must ensure the fixture is properly vented. Which arrangement best meets the requirement?

  1. Connect the toilet directly to the soil stack with no vent
  2. Provide a vent that connects to the fixture drain within the required distance from the trap Correct answer.
  3. Use an air admittance valve on the toilet cistern
  4. Install a vent only at the top of the stack

Explanation

A fixture drain must be vented within the code-specified distance from the trap to protect the trap seal. Venting only at the top of the stack may not adequately protect a fixture on a long branch.

Question 23Sanitary plumbing and drainage systems

What is the main reason for installing a trap primer on a floor waste gully in a commercial kitchen?

  1. To prevent grease from entering the drain
  2. To vent the gully to the atmosphere
  3. To increase the flow rate of the gully
  4. To maintain the water seal by regularly adding water to the trap Correct answer.

Explanation

A trap primer automatically adds a small amount of water to the trap to replace evaporation and maintain the seal. This is important where the gully is not regularly used and the seal could otherwise dry out.

Question 24Sanitary plumbing and drainage systems

A drainage system in a high-rise building experiences noise and pressure fluctuations when fixtures discharge. Which design change is most likely to reduce these effects?

  1. Reducing the gradient of the horizontal branches
  2. Removing the trap from the lowest fixture
  3. Installing a relief vent and properly sizing the vent stack Correct answer.
  4. Increasing the diameter of the branch drains

Explanation

Relief vents and correctly sized vent stacks help equalise pressure in tall drainage systems and reduce noise and trap seal loss. Venting design is critical in high-rise buildings where flow velocities and pressure variations are greater.

Question 25Sanitary plumbing and drainage systems

A plumber is asked to connect a new fixture to an existing drainage system in a heritage building. The existing vent may be undersized. What is the most appropriate action?

  1. Assess the vent capacity and upgrade it if necessary to protect trap seals Correct answer.
  2. Connect the fixture without checking the vent, as the existing system has worked for years
  3. Install a larger trap on the new fixture only
  4. Block the existing vent to prevent noise

Explanation

Adding a fixture increases the demand on the venting system, so the vent capacity must be assessed and upgraded if required. Undersized venting can cause trap seal loss and must be corrected to maintain a safe system.

Question 26Sanitary plumbing and drainage systems

Under a sanitary drainage design, what is the minimum internal diameter commonly required for a vent stack serving a soil stack in a multi-storey building?

  1. 40 mm
  2. 50 mm Correct answer.
  3. 100 mm
  4. 32 mm

Explanation

Vent stacks are generally sized at not less than 50 mm internal diameter to allow adequate air movement and to resist blockage from frost or debris. A smaller diameter cannot reliably equalise pressures across the height of the stack. Larger diameters such as 100 mm are permitted but are not the minimum.

Question 27Sanitary plumbing and drainage systems

A soil fixture discharges into a drainage system. Which component is installed immediately downstream of the fixture outlet to maintain a water seal?

  1. A fixture trap Correct answer.
  2. A boundary trap
  3. A reflux valve
  4. An inspection shaft

Explanation

Each fixture that discharges to the drainage system must be protected by its own trap, which retains a water seal against sewer gas. The trap is located directly at or below the fixture outlet. Boundary traps, inspection shafts and reflux valves serve other functions in the system.

Question 28Sanitary plumbing and drainage systems

A horizontal sanitary drain is laid at a constant grade. Which statement describes the correct relationship between pipe size and minimum gradient?

  1. Smaller pipes require a flatter gradient to prevent self-siphoning
  2. Larger pipes may use a flatter gradient because they carry the same depth of flow
  3. Larger pipes may use a flatter gradient because they achieve self-cleansing velocity at lower slopes Correct answer.
  4. Gradient is independent of pipe size and is set only by the available fall

Explanation

Self-cleansing velocity depends on the hydraulic radius, so a larger pipe reaches the required velocity at a flatter slope. Codes therefore permit reduced minimum gradients as diameter increases. Smaller pipes need steeper gradients to avoid solids settling.

Question 29Sanitary plumbing and drainage systems

A vent pipe serving a drainage system must terminate in the open air. Which termination detail is required to protect the vent outlet?

  1. A cowl or return bend to exclude rain and birds Correct answer.
  2. A flush finish level with the roof surface
  3. A cap cemented over the pipe end
  4. A mesh screen sealed to the pipe with no opening

Explanation

Vent terminals are fitted with a cowl, return bend or similar fitting that keeps rain and vermin out while still allowing free air movement. The vent must remain open to atmosphere. Sealing or capping the vent defeats its purpose.

Question 30Sanitary plumbing and drainage systems

A 150 mm diameter drain must fall 0.45 m over a 30 m run. What gradient does this represent?

  1. 1 in 50
  2. 1 in 75
  3. 1 in 90
  4. 1 in 67 Correct answer.

Explanation

Gradient is the fall divided into the run: 30 divided by 0.45 equals 66.7, so the grade is approximately 1 in 67. This is within typical limits for a 150 mm drain. The other ratios do not match the stated fall and run.

Question 31Sanitary plumbing and drainage systems

A 100 mm fixture branch connects to a vertical soil stack. Which fitting arrangement is preferred to reduce turbulence and prevent cross-flow into the branch?

  1. A straight tee with the branch at right angles to the stack
  2. A double tee with both branches entering at right angles
  3. A reducing coupling fitted directly to the stack
  4. A swept junction with the branch entering in the direction of flow Correct answer.

Explanation

A swept junction directs flow smoothly down the stack and minimises turbulence and pressure fluctuation that could siphon branch traps. Right-angle tees cause abrupt changes in direction and promote cross-flow. The swept fitting is standard practice for branch connections.

Question 32Sanitary plumbing and drainage systems

A floor waste gully in a large commercial kitchen is rarely used, and its trap seal is evaporating. What is the most appropriate solution?

  1. Fit a larger gully grating
  2. Seal the gully with a solid cover
  3. Increase the gully riser height
  4. Install a trap primer connected to a fixture supply Correct answer.

Explanation

A trap primer delivers a small, regular flow of water to the trap to maintain the seal where the fixture is infrequent. Evaporation is the cause, so the remedy is to replenish water. Sealing the gully would defeat its drainage function and create a trap seal loss elsewhere.

Question 33Sanitary plumbing and drainage systems

A plumber is testing a new sanitary drainage system before backfilling. Which test method checks the pipework for leaks by filling the system with water?

  1. Hydrostatic water test Correct answer.
  2. Air pressure test
  3. Smoke test
  4. Dye test

Explanation

A hydrostatic test fills the system with water, often to a specified head, and holds it while joints are inspected for leaks. It is the standard test for newly installed buried drainage. Air, smoke and dye tests serve other diagnostic purposes.

Question 34Sanitary plumbing and drainage systems

A basement fixture is below the level of the public sewer. What drainage arrangement is required to discharge its waste?

  1. A pumped system with a collecting well and pumps Correct answer.
  2. A larger diameter gravity drain
  3. A gravity drain with a steeper gradient
  4. A reflux valve on the basement drain

Explanation

Where fixtures are below the sewer invert, waste cannot flow by gravity, so a collecting well with pumps lifts the discharge to the gravity system. A reflux valve alone would not lift the waste and would not allow the basement to drain. Gravity options cannot overcome the level difference.

Question 35Sanitary plumbing and drainage systems

A vent pipe passes through a roof space where temperatures fall below freezing. What is the main risk to the drainage system if the vent is not protected?

  1. The vent pipe will expand and crack the roof
  2. The vent will draw sewer gas into the building
  3. The pipe will lose its gradient and pond water
  4. Frost may block the vent, causing trap seal loss Correct answer.

Explanation

Frost can form in the vent terminal or pipe and restrict airflow, which leads to pressure imbalance and trap seal loss when fixtures discharge. Vent pipes in cold roof spaces may need insulation or a frost-resistant terminal. The other outcomes are not the primary consequence of a frozen vent.

Question 36Sanitary plumbing and drainage systems

A plumber is installing an air admittance valve (AAV) on a fixture branch in a building. Which condition must be satisfied for the AAV to function correctly?

  1. It must be sealed inside a wall cavity with no ventilation
  2. It must be installed in a location with free air access and protected from debris Correct answer.
  3. It must be installed below the fixture trap
  4. It must be connected to the soil stack below the lowest branch

Explanation

An AAV admits air when negative pressure occurs but must have free air access to operate, and it must be protected from debris and moisture. It is installed above the fixture trap, not below it. Enclosing it in a sealed cavity prevents it from functioning.

Question 37Sanitary plumbing and drainage systems

A drainage system in a high-rise building experiences pressure fluctuations when many fixtures discharge simultaneously. Which design measure best reduces these fluctuations?

  1. Adding relief vents or a vent stack at intervals Correct answer.
  2. Increasing the number of fixture traps
  3. Removing the stack vent
  4. Reducing the diameter of the soil stack

Explanation

Relief vents or a parallel vent stack equalise pressure in tall drainage systems and prevent trap seal loss. Reducing the stack diameter would worsen pressure variations. Adding traps does not address pressure, and removing the vent makes the problem far worse.

Question 38Sanitary plumbing and drainage systems

A combined drainage system carries sewage and stormwater. Which statement correctly describes a combined system?

  1. Stormwater and sewage are carried in the same pipe to the public sewer Correct answer.
  2. Stormwater is treated on site before joining the sewer
  3. Stormwater is discharged to soakage while sewage goes to the sewer
  4. Stormwater and sewage are carried in separate pipes to the property boundary

Explanation

In a combined system, a single pipe carries both sewage and stormwater to the public combined sewer. Separate systems keep the two flows apart. On-site treatment and soakage describe other arrangements, not a combined system.

Question 39Sanitary plumbing and drainage systems

A 100 mm horizontal drain receives discharge from a group of fixtures. Which condition is most likely to cause the trap seals to be lost by siphonage?

  1. A drain gradient that is too flat
  2. A drain gradient that is too steep
  3. A drain pipe that is too large for the flow
  4. A vent pipe that is too small or partially blocked Correct answer.

Explanation

Inadequate venting allows negative pressure to develop downstream of a discharging fixture, which siphons the trap seal. A vent that is undersized or blocked cannot admit air to balance the pressure. Gradient and pipe size affect flow velocity and self-cleansing but are not the primary cause of siphonage.

Question 40Sanitary plumbing and drainage systems

A new fixture is to be connected to an existing drainage system in a heritage building where the vent may be inadequate. Which approach best ensures the new work performs correctly?

  1. Discharge the fixture to a soakage pit instead of the drain
  2. Increase the fixture trap depth to compensate for poor venting
  3. Install a new vent or AAV for the fixture and verify the existing vent capacity Correct answer.
  4. Connect the fixture without a vent to avoid altering the heritage fabric

Explanation

Where the existing vent cannot be relied on, the new fixture must be given its own vent or an AAV, and the existing vent capacity should be verified to ensure the whole system remains balanced. Increasing trap depth does not compensate for inadequate venting, and discharging to soakage is not acceptable for sanitary waste.

Question 41Water supply and backflow prevention

Under a typical plumbing code, what is the minimum required air gap for a potable water supply discharging into a receiving receptacle?

  1. Half the diameter of the supply pipe
  2. Equal to the diameter of the drain outlet
  3. Twice the effective diameter of the supply pipe
  4. One inch or twice the pipe diameter, whichever is greater Correct answer.

Explanation

The standard minimum air gap is one inch or twice the effective diameter of the supply pipe opening, whichever is larger. This separation prevents cross-connection by backflow even if the receptacle floods. A smaller gap risks contact between the supply outlet and contaminated liquid.

Question 42Water supply and backflow prevention

Which backflow prevention device relies on a differential pressure across two independently acting check valves to maintain protection?

  1. Atmospheric vacuum breaker
  2. Double check valve assembly
  3. Pressure vacuum breaker
  4. Reduced pressure principle assembly Correct answer.

Explanation

A reduced pressure principle assembly uses two check valves plus a differential relief valve that opens when pressure reverses, providing the highest protection for high-hazard applications. The relief valve discharges to atmosphere to protect the potable supply. This design allows it to handle both backpressure and backsiphonage.

Question 43Water supply and backflow prevention

A hose bibb in a residential yard is used to fill a pesticide sprayer with a submerged hose. Which protection method is the minimum acceptable for this connection?

  1. Air gap with a receiver tank
  2. Double check valve assembly at the meter
  3. No protection is required for residential use
  4. Screw-on vacuum breaker at the bibb Correct answer.

Explanation

A hose connection that can be submerged creates a cross-connection, so a hose-bibb vacuum breaker is the minimum required protection. It prevents backsiphonage into the potable supply when pressure drops. Larger assemblies are not required for a simple hose bibb.

Question 44Water supply and backflow prevention

Which water service pipe material is generally prohibited for potable water where it may be subject to lead leaching?

  1. Cross-linked polyethylene
  2. Copper tubing
  3. Galvanized steel
  4. Lead pipe Correct answer.

Explanation

Lead pipe is prohibited for potable water because it can leach lead into the supply and cause serious health effects. Copper, PEX, and galvanized steel are commonly permitted materials subject to local code. The prohibition is based on contamination risk, not structural strength.

Question 45Water supply and backflow prevention

What is the primary purpose of a water hammer arrestor installed near a quick-closing valve?

  1. To prevent backflow into the supply
  2. To filter sediment from the supply
  3. To increase water pressure at the fixture
  4. To absorb pressure surges caused by sudden valve closure Correct answer.

Explanation

A water hammer arrestor contains a cushion of air or a piston that absorbs the pressure surge when flow stops abruptly. This protects piping and fittings from damaging shock. It does not filter, boost pressure, or provide backflow protection.

Question 46Water supply and backflow prevention

In a potable water distribution system, what does the term 'fixture unit' represent?

  1. A measure of the probable flow demand of a fixture Correct answer.
  2. The maximum pressure a fixture can withstand
  3. The physical size of a fixture drain
  4. The volume of water a fixture holds

Explanation

A fixture unit is a dimensionless measure of the probable rate of flow and time of use of a fixture. It is used to size supply and drainage piping based on expected simultaneous demand. It is not a physical dimension or pressure rating.

Question 47Water supply and backflow prevention

Which condition is most likely to cause backsiphonage into a potable water system?

  1. A closed shutoff valve downstream of a fixture
  2. A rise in supply pressure above normal
  3. A water meter installed at the property line
  4. A pressure drop in the supply main Correct answer.

Explanation

Backsiphonage occurs when negative or reduced pressure in the supply main draws contaminated water back through a cross-connection. A sudden pressure drop, such as from a main break or heavy demand, creates this condition. Backpressure, by contrast, comes from a downstream pressure source.

Question 48Water supply and backflow prevention

A pressure vacuum breaker may not be installed where which condition exists?

  1. It is installed above the highest downstream outlet
  2. It is protected from freezing
  3. It is subject to continuous pressure for more than 12 hours Correct answer.
  4. It is installed with a test cock

Explanation

A pressure vacuum breaker has a check and an air inlet that must be able to open; continuous pressure can hold the air inlet closed and defeat protection. Codes limit it to no more than 12 hours of continuous pressure. It must still be installed above the highest downstream outlet.

Question 49Water supply and backflow prevention

What is the correct test sequence start for a reduced pressure principle backflow assembly?

  1. Open test cock 1 and record the static line pressure Correct answer.
  2. Open test cock 2 and observe the relief valve discharge
  3. Close the upstream shutoff valve first
  4. Open the downstream shutoff valve fully

Explanation

Testing begins by opening test cock 1 to establish line pressure and confirm the first check holds. Subsequent steps check the relief valve opening point and the second check. Closing valves or opening downstream first would not establish the baseline reading.

Question 50Water supply and backflow prevention

A water main break causes a sudden loss of pressure in a neighborhood. Which device provides protection for a commercial irrigation system connected to that main?

  1. Check valve at the pump discharge
  2. Atmospheric vacuum breaker on each head
  3. Pressure reducing valve at the meter
  4. Reduced pressure principle assembly at the service connection Correct answer.

Explanation

An RPZ assembly protects against both backsiphonage and backpressure at the service connection, making it suitable for irrigation hazards. A main break creates backsiphonage risk that requires a device with relief capability. Simple check valves and pressure valves do not provide cross-connection protection.