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Red Seal Plumber practice questions

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Question 1Plumbing systems planning, installation, testing and servicing

When sizing a water service pipe for a single-family dwelling using the fixture-unit method, which factor must be applied to the total fixture-unit count before selecting the pipe size from the sizing table?

  1. The developed length of the building supply and the available pressure differential Correct answer.
  2. The number of storeys served above the meter
  3. The total drainage fixture units connected downstream
  4. The heating capacity of the domestic hot water tank

Explanation

Water pipe sizing by fixture units requires converting the fixture-unit total into an equivalent demand and then checking that the available pressure can push that flow through the developed length of piping. Both the developed length and the pressure differential between the supply and the fixture determine the allowable pressure loss per unit length.

Question 2Plumbing systems planning, installation, testing and servicing

A lavatory drain is connected to a branch with a vertical drop of 1.5 m before it reaches the horizontal branch. What is the minimum trap arm length requirement that governs this connection?

  1. The trap arm may be any length provided the trap is vented
  2. The trap arm must be exactly twice the trap seal depth
  3. The trap arm must not exceed the developed length permitted for the pipe size, and the vent must be taken before the fall exceeds one pipe diameter Correct answer.
  4. The trap arm must be at least 1.5 m long

Explanation

A trap arm must be vented before the pipe falls more than one pipe diameter, otherwise the trap becomes a crown-vented S-trap that siphons. The maximum developed length of the trap arm is also limited by pipe size to keep the air path open.

Question 3Plumbing systems planning, installation, testing and servicing

Which material is generally prohibited for use as an underground building drain because it is subject to deformation and joint failure under backfill loads?

  1. PVC Schedule 40 DWV
  2. Cast iron soil pipe
  3. Vitrified clay pipe
  4. Copper drainage tube Type DWV Correct answer.

Explanation

Copper drainage tube is not commonly approved for buried building drains because thin-wall copper can deform and its soldered joints are vulnerable under backfill and soil movement. Cast iron, PVC DWV and vitrified clay are all accepted buried drainage materials where installed to code.

Question 4Plumbing systems planning, installation, testing and servicing

What is the primary purpose of installing a backwater valve on a basement fixture branch?

  1. To equalize pressure in the vent stack
  2. To regulate the flow of storm water into the sanitary drain
  3. To stop sewage from reversing into the basement when the public sewer surcharges Correct answer.
  4. To prevent sewer gas from entering the building

Explanation

A backwater valve is a one-way check device that closes when flow reverses, protecting low-level fixtures from surcharge in the public sewer. It is required where fixtures are below the level of the next upstream manhole cover.

Question 5Plumbing systems planning, installation, testing and servicing

A plumbing drawing shows a soil stack rising through a two-storey house. At what point must the stack be vented to the outside?

  1. At the base of the stack below the lowest branch
  2. At every fixture connection
  3. Only where the stack changes direction
  4. Only at the top of the stack above the roof Correct answer.

Explanation

A soil stack is extended full size through the roof to vent the drainage system and relieve pressure. The roof extension must terminate in open air clear of windows and air intakes as specified by code.

Question 6Plumbing systems planning, installation, testing and servicing

What is the minimum air gap required between a fixture outlet and the flood-level rim of a receiving receptacle for a typical plumbing fixture?

  1. Equal to the diameter of the outlet
  2. Twice the diameter of the outlet Correct answer.
  3. One half the diameter of the outlet
  4. 25 mm regardless of outlet size

Explanation

The standard air gap is twice the effective diameter of the fixture outlet, with a minimum absolute dimension. This prevents backflow by ensuring that a cross-connection cannot form even under surcharge.

Question 7Plumbing systems planning, installation, testing and servicing

During a hydrostatic test of a new DWV system, what is the typical minimum test pressure and duration for a system that will be tested with water?

  1. A 1 m head of water maintained for 30 minutes
  2. A 10 m head of water maintained for 2 hours
  3. A 3 m head of water maintained for 4 hours
  4. A 3 m head of water maintained for 15 minutes Correct answer.

Explanation

DWV systems are commonly tested with a 3 m head of water held for at least 15 minutes before inspection, with all joints exposed and checked for leaks. Some jurisdictions allow a 10 m head for certain systems, but the standard minimum is the 3 m head.

Question 8Plumbing systems planning, installation, testing and servicing

A fixture drain serving a water closet must connect to the branch using which type of fitting?

  1. A sanitary tee on its back
  2. A double sanitary tee
  3. A wye or combination wye-and-eighth bend Correct answer.
  4. A reducing coupling

Explanation

Water closets and other fixtures with large solids discharge require a wye or combination fitting so flow enters the branch in the direction of travel and solids do not accumulate. Sanitary tees are restricted to vertical-to-horizontal connections where flow is not likely to clog.

Question 9Plumbing systems planning, installation, testing and servicing

A plumber is installing a water heater in a basement and must provide a temperature and pressure relief valve discharge. Where must the discharge pipe terminate?

  1. Into the sanitary drainage system through a trapped connection
  2. Directly into the floor drain trap
  3. To a point within 150 mm of the floor in a manner that prevents scalding Correct answer.
  4. To the exterior of the building above the roof line

Explanation

The T&P relief discharge must terminate in a safe place, typically within 150 mm of the floor, so that hot water or steam is released without scalding occupants. It must not be connected directly to drainage in a way that allows backflow or blockage.

Question 10Plumbing systems planning, installation, testing and servicing

In a commercial kitchen, a pre-rinse spray valve is installed on a sink. Which backflow protection method is appropriate for this connection?

  1. A vacuum breaker on the hose Correct answer.
  2. A hose bibb vacuum breaker is sufficient
  3. A reduced-pressure principle backflow preventer on the building main
  4. An air gap at the sink rim

Explanation

A hose-connected spray valve at a sink is protected by an atmospheric or hose-connection vacuum breaker installed at the outlet, which prevents back-siphonage from the hose. A building-level RPZ does not protect against a local cross-connection at the fixture.

Question 11Plumbing systems planning, installation, testing and servicing

A building has a water service entering at 350 kPa static pressure. The building is 20 m tall and the highest fixture is 18 m above the meter. What is the approximate residual pressure at the highest fixture before friction losses?

  1. Approximately 525 kPa
  2. Approximately 0 kPa
  3. Approximately 175 kPa Correct answer.
  4. Approximately 350 kPa

Explanation

Static pressure drops by roughly 10 kPa per metre of elevation, so 18 m of rise reduces pressure by about 180 kPa. Subtracting this from 350 kPa leaves approximately 170 kPa, close to 175 kPa, before friction losses are considered.

Question 12Plumbing systems planning, installation, testing and servicing

A horizontal drain 75 mm in diameter runs 12 m and must be installed with uniform slope. What is the minimum fall required for a 1 in 50 slope?

  1. 60 mm
  2. 240 mm Correct answer.
  3. 360 mm
  4. 120 mm

Explanation

A 1 in 50 slope over 12 m requires 12 000 mm divided by 50, which equals 240 mm of fall. Slope is expressed as a ratio of fall to run, so the calculation is straightforward.

Question 13Plumbing systems planning, installation, testing and servicing

A vent stack serving a bathroom group is installed in a cold climate. Which installation detail prevents frost closure at the roof termination?

  1. Increasing the vent size at least one nominal size above the minimum through the roof Correct answer.
  2. Extending the vent only 150 mm above the roof
  3. Installing a rain cap directly on the vent
  4. Reducing the vent diameter at the roof

Explanation

In areas subject to frost, the vent must be increased at least one nominal pipe size above the minimum through the roof and flashing to prevent frost from closing the opening. This is a recognized cold-climate requirement.

Question 14Plumbing systems planning, installation, testing and servicing

A pump discharges into a drainage sump. Which detail is required to prevent the pump discharge from creating a cross-connection with the drainage system?

  1. An air gap between the discharge pipe and the sump flood level Correct answer.
  2. A vacuum breaker on the discharge pipe
  3. A check valve on the discharge line
  4. A trap on the sump inlet

Explanation

Any pipe discharging into a drainage receptacle must maintain an air gap above the flood level rim to prevent backflow. A check valve and trap do not provide the physical separation needed for cross-connection control.

Question 15Plumbing systems planning, installation, testing and servicing

Which of the following is the correct method for testing a new gas piping system installed in a commercial building before it is placed in service?

  1. A soap bubble test at operating pressure only
  2. A vacuum test on the piping
  3. A pressure test with air or inert gas at a pressure and duration specified by code, with the gauge observed for leakage Correct answer.
  4. A flow test with gas at operating pressure

Explanation

Gas piping must be pressure-tested with air, inert gas or gas at a specified test pressure for a specified period, and the gauge must show no drop. Soap bubble testing is only a supplementary leak check, not the acceptance test.

Question 16Plumbing systems planning, installation, testing and servicing

A plumber must install a cleanout at the base of a stack. What is the maximum distance a cleanout may be located from the base of the stack where the stack is more than 1.5 m from the building drain?

  1. The cleanout may be located anywhere on the horizontal branch
  2. The cleanout must be installed at the base of the stack within the distance allowed by code, typically not more than 1.5 m above the floor Correct answer.
  3. The cleanout must be installed on the roof
  4. Cleanouts are never required at the base of a stack

Explanation

A cleanout is required at the base of every stack, and where the stack does not connect directly to the building drain, the cleanout is placed at the base within the code-specified distance above the floor. This provides access for rodding the stack and building drain.

Question 17Plumbing systems planning, installation, testing and servicing

A 100 mm diameter building drain must pass under a footing. Which method of protection is required?

  1. The pipe must be replaced with a smaller diameter
  2. The pipe may be installed without protection if it is PVC
  3. The pipe must be encased in concrete or sleeved with provisions for settlement Correct answer.
  4. The pipe may be installed in a sleeve with the annular space sealed

Explanation

Where a building drain passes under a footing, the pipe must be protected against differential settlement and loads, typically by encasement in concrete or a properly sized sleeve. This prevents shear failure at the footing.

Question 18Plumbing systems planning, installation, testing and servicing

In a multi-storey building, a vent stack is offset horizontally to clear a structural beam. What is the minimum slope required for the offset portion of the vent?

  1. The offset must be vertical only
  2. The offset may be installed level
  3. The offset must be installed with a slope back to the stack of at least 1 in 50 Correct answer.
  4. The offset must slope away from the stack at 1 in 100

Explanation

Horizontal offsets in vent piping must slope back toward the stack so that condensate and rainwater drain back rather than collect and block the vent. A slope of at least 1 in 50 is the recognized minimum.

Question 19Plumbing systems planning, installation, testing and servicing

A water closet is installed in a public washroom and must meet accessibility requirements. What is the required height of the water closet seat above the finished floor?

  1. 430 mm to 480 mm Correct answer.
  2. 300 mm to 350 mm
  3. 380 mm to 400 mm
  4. 500 mm to 550 mm

Explanation

Accessible water closets are installed with the seat height between approximately 430 mm and 480 mm above the finished floor. This range accommodates transfer from a wheelchair while remaining usable for ambulatory users.

Question 20Plumbing systems planning, installation, testing and servicing

A plumber is installing a grease interceptor for a restaurant. Which factor determines the required capacity of the interceptor?

  1. The height of the vent stack
  2. The total fixture-unit count of the drainage system
  3. The number and type of fixtures discharging grease-laden waste and the retention time required Correct answer.
  4. The size of the building water service

Explanation

Grease interceptor sizing is based on the flow rate and grease load from the fixtures served, along with the retention time needed for separation. Fixture units, water service size and vent height do not directly determine grease interceptor capacity.

Question 21Plumbing systems planning, installation, testing and servicing

A building's water supply system experiences water hammer when a solenoid valve closes quickly. Which solution best addresses the cause?

  1. Increasing the pipe diameter throughout the system
  2. Installing a pressure-reducing valve at the meter
  3. Installing an arrestor near the quick-closing valve Correct answer.
  4. Removing the check valve from the service line

Explanation

Water hammer is caused by the sudden stop of flow creating a pressure surge, and an arrestor installed close to the quick-closing valve absorbs that surge. A pressure-reducing valve lowers static pressure but does not absorb the surge itself.

Question 22Plumbing systems planning, installation, testing and servicing

A drainage system serving a high-rise building requires a vertical stack with branches at each floor. Which design consideration most affects the need for a relief vent?

  1. The total number of fixtures on the stack
  2. The stack height and the resulting pneumatic pressure fluctuations Correct answer.
  3. The material of the stack
  4. The diameter of the building drain

Explanation

Tall stacks develop significant pneumatic pressure fluctuations from the falling water, which can siphon traps on lower floors. Relief vents are used to equalize pressure in stacks exceeding the height limits set by code.

Question 23Plumbing systems planning, installation, testing and servicing

A commercial building has a fire sprinkler system connected to the domestic water supply. Which backflow prevention assembly is typically required at the connection point?

  1. A hose bibb vacuum breaker
  2. A reduced-pressure principle backflow preventer Correct answer.
  3. A double check valve assembly
  4. An atmospheric vacuum breaker

Explanation

A fire sprinkler system connection is a high-hazard cross-connection because of stagnant water, chemicals and possible booster pumps, so a reduced-pressure principle backflow preventer is required. A double check valve is used only for lower-hazard connections.

Question 24Plumbing systems planning, installation, testing and servicing

A plumber is commissioning a new hot water recirculation system in a large building. Which factor most directly determines the required pump head?

  1. The number of fixtures served
  2. The total length of the hot water piping and the pressure drop through the return loop Correct answer.
  3. The diameter of the cold water service
  4. The capacity of the water heater

Explanation

Recirculation pump head must overcome friction losses through the longest supply path and the return loop, which depend on pipe length, fittings and flow rate. Heater capacity, fixture count and cold service size do not determine the head requirement.

Question 25Plumbing systems planning, installation, testing and servicing

A storm drainage system on a flat roof must be designed to prevent ponding. Which combination of features is most appropriate?

  1. Downspouts discharging onto the roof surface
  2. A single roof drain at the low point with no overflow
  3. Roof drains connected to the sanitary sewer
  4. Roof drains with strainers, overflow scuppers or secondary drains, and a slope to the drains Correct answer.

Explanation

Flat roof drainage requires primary roof drains with strainers, secondary or overflow drainage to handle blockage or exceedance, and adequate slope to direct water to the drains. Connecting storm drainage to the sanitary sewer is generally prohibited.

Question 26Plumbing systems planning, installation, testing and servicing

A plumber is sizing a water distribution system and needs to determine the probable demand for a building. Which quantity is the starting point for using fixture unit values?

  1. The developed length of the longest run
  2. The diameter of the building drain
  3. The static pressure at the meter outlet
  4. The total number of fixture units connected to the system Correct answer.

Explanation

Sizing begins with summing the fixture units of all fixtures served, then converting that total to probable demand using the appropriate fixture unit-to-flow table. Developed length and pressure are used later to check whether that demand can be delivered.

Question 27Plumbing systems planning, installation, testing and servicing

When joining copper tube to a bronze pump housing in a potable water line, which practice prevents galvanic corrosion at the connection?

  1. Apply pipe dope to the threads before assembly
  2. Install a dielectric union between the dissimilar metals Correct answer.
  3. Wrap the joint with silicone tape
  4. Increase the pipe size at the pump flange

Explanation

Copper and bronze in contact with an electrolyte can drive galvanic corrosion; a dielectric union breaks the metallic path between the two materials. Pipe dope and tape seal threads but do not interrupt electrical continuity.

Question 28Plumbing systems planning, installation, testing and servicing

A plumber is installing a floor drain in a commercial washroom and must provide a trap primer. What is the purpose of the trap primer?

  1. To prevent debris from entering the drain body
  2. To maintain the trap seal by replenishing water lost to evaporation Correct answer.
  3. To vent the drain line to the stack
  4. To increase the flow rate through the floor drain

Explanation

Floor drains that see little use lose their trap seal through evaporation, allowing sewer gas into the building. A trap primer delivers a small amount of water periodically to keep the seal intact.

Question 29Plumbing systems planning, installation, testing and servicing

A plumber is pressure-testing a new potable water system with water. Which result indicates the test has been successfully completed?

  1. The system reaches test pressure briefly and then is drained
  2. The system holds the specified test pressure for the required duration with no drop beyond allowance Correct answer.
  3. The system is tested at working pressure only
  4. The system shows a small continuous drop that stabilizes

Explanation

A hydrostatic test is passed when the system holds the specified pressure for the required time without leakage or unacceptable pressure loss. A continuing drop indicates a leak or trapped air that must be resolved.

Question 30Plumbing systems planning, installation, testing and servicing

A plumber is installing a lavatory in a public washroom and must meet barrier-free requirements. Which installation detail supports accessibility?

  1. Insulating the supply and waste pipes under the lavatory Correct answer.
  2. Installing the faucet with a single cross handle
  3. Reducing the drain size to increase velocity
  4. Mounting the mirror directly above the faucet

Explanation

Protective insulation on exposed supply and drain piping under a barrier-free lavatory prevents contact burns and injury to a seated user. Accessibility standards require the pipes to be wrapped or otherwise protected.

Question 31Plumbing systems planning, installation, testing and servicing

A plumber is roughing in a horizontal branch serving a water closet and must select the fitting where the closet bend connects to the branch. Which fitting type is required at this change of direction?

  1. A double sanitary tee
  2. A vent tee
  3. A sanitary tee installed on its back
  4. A long-radius bend or a pattern that provides a sweeping flow path Correct answer.

Explanation

Drainage fittings must provide a smooth, sweeping path so solids are not caught at the change of direction. Long-radius bends and drainage patterns are designed for this purpose, whereas vent fittings are not.

Question 32Plumbing systems planning, installation, testing and servicing

A plumber is installing a water heater and must route the temperature and pressure relief valve discharge. Which installation satisfies the requirements?

  1. Terminate the discharge inside the heater enclosure
  2. Route the discharge to a safe point of disposal with gravity flow and no valve or reduction Correct answer.
  3. Route the discharge to a floor drain through a reduced-diameter copper tube
  4. Install a shutoff valve on the discharge to allow servicing

Explanation

The T&P relief discharge must run full size, by gravity, to a safe point of disposal and must not be trapped, valved, or reduced. Any restriction can prevent the valve from relieving pressure safely.

Question 33Plumbing systems planning, installation, testing and servicing

A plumber is designing a venting arrangement for a battery of fixtures on one floor. Which condition requires a relief vent?

  1. A stack serving more than the permitted number of branch intervals Correct answer.
  2. A floor drain with a trap primer
  3. A single lavatory on a short branch
  4. A water closet connected to a vertical stack

Explanation

When a stack carries more than the permitted number of branch intervals, a relief vent is required to protect trap seals from pressure fluctuations. A single small fixture group does not trigger that requirement.

Question 34Plumbing systems planning, installation, testing and servicing

A plumber is installing a water service and must protect it where it passes through a foundation wall. Which detail is required?

  1. Provide a sleeve or annular space to allow movement and prevent shear damage Correct answer.
  2. Reduce the pipe diameter at the wall
  3. Embed the pipe rigidly in the concrete
  4. Install a check valve at the wall penetration

Explanation

A sleeve or clearance around the service pipe prevents the wall from shearing or crushing the pipe as the building settles. Rigid embedding removes that protection.

Question 35Plumbing systems planning, installation, testing and servicing

A plumber is sizing a gas line for a commercial range. Which factor most directly increases the required pipe diameter for a given appliance input?

  1. A longer developed length of piping Correct answer.
  2. A larger building footprint
  3. A higher supply pressure at the meter
  4. A higher appliance efficiency rating

Explanation

Pressure loss from friction increases with developed length, so a longer run requires a larger pipe to deliver the same input at the required pressure. Higher supply pressure, by contrast, can allow a smaller pipe.

Question 36Plumbing systems planning, installation, testing and servicing

A plumber is installing a sewage ejector pit in a basement. Which detail is required to control odors and prevent sewer gas from entering the building?

  1. Seal the pit and omit venting
  2. Provide a tight pit cover with a vent connected to the venting system Correct answer.
  3. Discharge the pit directly to the storm system
  4. Install a floor drain in the pit connected to the building drain

Explanation

An ejector pit receiving sewage must have a gas-tight cover and be vented to the outside through the venting system. An unvented or open pit releases sewer gas into the building.

Question 37Plumbing systems planning, installation, testing and servicing

A plumber is installing a backflow preventer on a boiler feed line connected to the potable system. Which device provides protection against both backsiphonage and backpressure?

  1. A reduced pressure principle assembly Correct answer.
  2. An air gap fitting at the fixture
  3. A vacuum breaker
  4. A dual check valve

Explanation

A reduced pressure principle assembly protects against both backpressure and backsiphonage and is required for hazardous cross-connections such as boiler feed lines. Vacuum breakers protect only against backsiphonage.

Question 38Plumbing systems planning, installation, testing and servicing

A plumber is installing a horizontal storm drain from a roof drain. Which condition must the pipe meet to drain freely?

  1. It must be level to prevent turbulence
  2. It must be installed with a trap at the roof drain
  3. It must slope away from the discharge point
  4. It must slope continuously toward the point of discharge Correct answer.

Explanation

Storm drainage must flow by gravity, so the pipe must slope continuously toward the discharge point. Level or reverse-sloped pipe allows ponding and debris accumulation.

Question 39Plumbing systems planning, installation, testing and servicing

A plumber is installing a potable water line near a sewer line in a trench. Which installation protects the potable water?

  1. Lay the water line directly below the sewer without separation
  2. Allow the lines to touch where the trench is narrow
  3. Connect the two lines with a bypass for testing
  4. Lay the water line above the sewer with adequate separation and use approved materials at crossings Correct answer.

Explanation

Water mains and sewers must be separated, with the water line generally above the sewer, and crossings must be constructed to prevent contamination. Direct contact or placing water below the sewer creates a contamination risk.

Question 40Plumbing systems planning, installation, testing and servicing

A plumber is installing a fixture that requires a trap with a specific water seal depth. What is the minimum water seal depth for a standard trap?

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

Explanation

A standard trap must maintain a water seal of at least 50 mm to resist sewer gas while remaining self-cleaning. Deeper seals are permitted within limits but the minimum is 50 mm.

Question 41Plumbing systems planning, installation, testing and servicing

A plumber is commissioning a booster pump serving upper floors. Which condition indicates the pump is cavitating?

  1. Lower motor current than rated
  2. Steady discharge pressure with quiet operation
  3. Noisy operation with vibration and reduced discharge pressure Correct answer.
  4. Increased flow at the highest fixture

Explanation

Cavitation occurs when the pump inlet pressure falls below the vapour pressure of the water, producing vapour bubbles that collapse and cause noise, vibration, and loss of performance. The remedy is to correct the suction conditions.

Question 42Plumbing systems planning, installation, testing and servicing

A plumber is installing a cleanout on a horizontal drainage line. Which location is acceptable?

  1. Only at the fixture trap
  2. At the end of the horizontal line and at changes of direction greater than 45 degrees Correct answer.
  3. Only where the line passes through a wall
  4. Only at the top of the stack

Explanation

Cleanouts are required at the end of horizontal runs and at changes of direction that exceed 45 degrees so the line can be rodded. They must remain accessible for maintenance.

Question 43Plumbing systems planning, installation, testing and servicing

A plumber is installing a water closet in a commercial building and must set the fixture level. Which practice ensures a proper seal at the closet flange?

  1. Omit the seal and rely on the bolts
  2. Use two stacked wax rings to raise the fixture
  3. Set the fixture with a new wax or elastomer seal compressed evenly onto the flange Correct answer.
  4. Grout the base before connecting the seal

Explanation

The closet seal must be a single properly sized gasket compressed evenly between the fixture horn and the flange. Stacking seals or omitting the seal creates leak paths.

Question 44Plumbing systems planning, installation, testing and servicing

A plumber is installing a recirculating hot water system in a large building. Which factor most directly determines the recirculation pump head requirement?

  1. The diameter of the building drain
  2. The pressure loss through the longest return loop plus the fixture demand Correct answer.
  3. The height of the vent stack
  4. The number of fixtures on the system

Explanation

The pump must overcome friction loss in the return loop while delivering the design recirculation flow, so the longest loop's pressure loss plus the required flow sets the head. Fixture count and drain size do not determine pump head.

Question 45Plumbing systems planning, installation, testing and servicing

A plumber is installing a floor drain in a concrete slab. Which detail prevents the drain body from being crushed or displaced during pouring?

  1. Secure the drain to the formwork and protect the opening during the pour Correct answer.
  2. Backfill around the drain with loose gravel only
  3. Cover the drain with a plastic sheet only
  4. Set the drain on the subgrade without anchoring

Explanation

The drain body must be anchored to the formwork and its opening protected so concrete placement does not move or fill it. Proper anchoring keeps the strainer at the finished floor elevation.

Question 46Plumbing systems planning, installation, testing and servicing

A plumber is installing a vent through a roof in a cold climate. Which detail prevents frost closure of the vent?

  1. Increase the vent diameter at least one size through the roof penetration Correct answer.
  2. Reduce the vent to the minimum size at the roof
  3. Install a screen with fine mesh over the vent
  4. Terminate the vent below the roof surface

Explanation

Moisture-laden air can freeze and close a small vent in cold weather, so the vent is increased at least one size through the roof. Fine screens and low termination aggravate frost and are not the remedy.

Question 47Plumbing systems planning, installation, testing and servicing

A plumber is installing a grease interceptor for a restaurant. Which sizing approach is appropriate?

  1. Size by the fixture capacity and flow rate of the fixtures discharging to the interceptor Correct answer.
  2. Size by the building's total water service diameter
  3. Size by the number of floor drains in the kitchen
  4. Size by the building drain slope

Explanation

Grease interceptor capacity is based on the flow rate and grease load of the fixtures connected to it, typically derived from fixture capacity. Service size and drain slope do not determine grease retention capacity.

Question 48Plumbing systems planning, installation, testing and servicing

A plumber is installing a water supply line and must provide a shutoff valve for a fixture. Which valve type allows throttling without damage to the seat?

  1. A butterfly valve used only for isolation
  2. A globe valve Correct answer.
  3. A check valve
  4. A gate valve

Explanation

A globe valve is designed for throttling because its plug moves perpendicular to the seat and can be partially closed without damaging the seating surfaces. Gate valves are intended for full-open or full-closed service.

Question 49Plumbing systems planning, installation, testing and servicing

A plumber is installing a drainage system in a high-rise building and must address stack flow. Which design measure reduces pressure fluctuations in the stack?

  1. Eliminate the vent at the top of the stack
  2. Provide a yoke vent or relief vent at intervals along the stack Correct answer.
  3. Reduce the stack diameter as height increases
  4. Connect the stack directly to the storm system

Explanation

Tall stacks develop high velocities and pressure swings, so yoke or relief vents are used to equalize pressure and protect trap seals. Reducing diameter or eliminating the top vent worsens the problem.

Question 50Plumbing systems planning, installation, testing and servicing

A plumber is installing a fixture drain and must maintain the required slope. Which statement describes the purpose of the slope on a horizontal drainage line?

  1. To increase the pressure within the drain
  2. To carry solids with the flow by gravity at a self-cleaning velocity Correct answer.
  3. To reduce the venting requirement
  4. To allow the trap to drain completely

Explanation

Horizontal drainage relies on gravity, and the prescribed slope produces a self-cleaning velocity that carries solids to the building drain. Slope does not create pressure or eliminate venting.