I85PREP
⌘ K
RBSE Sec Voc Plumbing study materials
RBSE Sec Voc Plumbing study resources

RBSE Sec Voc Plumbing practice questions

One question at a time. Build your RBSE Sec Voc Plumbing understanding.

First 50 of 199 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Trade Fundamentals, Tools, Materials and Safety

On a plumbing site, which item of personal protective equipment is specifically required when cutting galvanized pipe with a powered abrasive saw?

  1. Face shield with safety glasses beneath Correct answer.
  2. Cloth dust mask
  3. Steel-toed gumboots
  4. Rubber apron

Explanation

An abrasive cut-off saw throws hot metal particles and abrasive grit at high velocity toward the operator's face, so a face shield worn over safety glasses is the standard protection. The glasses alone do not stop particles reaching the cheeks and neck, while a face shield alone leaves gaps at the sides. Respiratory and foot protection are useful on site but do not address this specific hazard.

Question 2Trade Fundamentals, Tools, Materials and Safety

Which hand tool is designed to cut an opening in sheet metal for a fixture outlet in a duct or thin panel?

  1. Hole saw Correct answer.
  2. Aviation snips
  3. Hacksaw
  4. Torque wrench

Explanation

A hole saw consists of a cylindrical toothed blade on an arbor and cuts clean circular openings sized to fit valves, nipples, and fixture connections. Aviation snips cut along a line rather than producing a sized round hole, and a hacksaw is for straight cuts on pipe and stock. A torque wrench applies measured tightening force and does not cut material.

Question 3Trade Fundamentals, Tools, Materials and Safety

A length of copper tube is marked 1/2 inch nominal size. What does the nominal size of copper tube indicate?

  1. The exact outside diameter in inches
  2. The thread size of the fittings used on it
  3. The approximate inside diameter for which fittings are sized Correct answer.
  4. The inside diameter of the tube wall

Explanation

Copper water tube is designated by a nominal size that approximates the inside diameter, and fittings are catalogued to match that nominal size. The actual outside diameter is fixed per nominal size regardless of wall thickness, and it does not equal the nominal figure. Copper tube for water supply is joined by soldering or press fittings rather than by threads.

Question 4Trade Fundamentals, Tools, Materials and Safety

Which plastic piping material is joined by solvent cementing and is commonly used for drain, waste, and vent lines?

  1. Chlorinated polyvinyl chloride
  2. Polypropylene random copolymer
  3. Cross-linked polyethylene
  4. Polyvinyl chloride Correct answer.

Explanation

PVC is joined with solvent cement, which softens the mating surfaces so they fuse into a continuous joint, and it is widely used for DWV and cold-water lines. PEX is joined with mechanical or crimp fittings and is used mainly for hot and cold distribution. CPVC is a different material with different cement and temperature limits, and PP-R is joined by heat fusion.

Question 5Trade Fundamentals, Tools, Materials and Safety

A safety data sheet for a solvent cement shows a flash point of 15 degrees Celsius. What does this tell the worker?

  1. The cement is corrosive to skin only below 15 degrees Celsius
  2. The cement gives off flammable vapour at ordinary site temperatures Correct answer.
  3. The cement will not burn until heated above 15 degrees Celsius
  4. The cement is safe to store beside any heat source

Explanation

A flash point near or below normal ambient temperature means the liquid releases enough vapour to ignite at a spark or flame under everyday conditions. Solvent cements for PVC and CPVC are therefore kept away from open flame, pilot lights, and sparking tools, and the area is ventilated. The flash point is a flammability figure and says nothing about corrosivity.

Question 6Trade Fundamentals, Tools, Materials and Safety

What is the purpose of a plumbing trap seal in a drainage system?

  1. To increase flow velocity in the branch
  2. To hold a water seal that blocks sewer gas from entering the building Correct answer.
  3. To filter solids before they reach the stack
  4. To support the weight of the fixture

Explanation

The trap retains a measured depth of water that forms a barrier between the drainage system and the occupied space, preventing sewer gases from passing into the room. The depth of the seal, not the shape of the trap alone, determines how well it resists pressure fluctuations. Traps do not strain solids, carry fixture weight, or accelerate flow.

Question 7Trade Fundamentals, Tools, Materials and Safety

A worker must excavate a trench 1.8 metres deep in ordinary soil for a sewer line. Which precaution applies before anyone enters the trench?

  1. Wait until the sewer pipe is laid before assessing the walls
  2. Enter freely because the depth is below 2 metres
  3. Rely on the pipe bedding to keep the walls stable
  4. Provide a protective system such as sloping, shoring, or a trench box Correct answer.

Explanation

Trenches at this depth in ordinary soil require a protective system to guard against wall collapse, and the competent person must inspect the excavation before entry and as conditions change. Collapse can occur suddenly in apparently firm ground, so depth alone does not make entry safe. Bedding material at the bottom provides no support to the walls.

Question 8Trade Fundamentals, Tools, Materials and Safety

Which statement correctly describes the difference between a pipe wrench and a basin wrench?

  1. A pipe wrench is used only on plastic pipe because its jaws are smooth
  2. A basin wrench is designed for tightening large soil-pipe couplings
  3. A basin wrench has a long shank and a pivoting jaw for reaching a nut behind a sink bowl Correct answer.
  4. A pipe wrench has serrated jaws and is used on chrome-plated supply tubes

Explanation

A basin wrench is made for the cramped space under a sink, with a long shaft and a spring-loaded pivoting jaw that grips a nut that is out of direct reach. A pipe wrench has hardened serrated jaws that bite into iron and steel pipe but would damage finished chrome. Neither tool is intended for plastic soil couplings or smooth-jawed work.

Question 9Trade Fundamentals, Tools, Materials and Safety

A plumber needs to join two lengths of large-diameter cast iron soil pipe with a flexible coupling. Which material is normally used for the gasket in a no-hub coupling?

  1. Threaded couplings with pipe dope
  2. Neoprene or rubber sleeve clamped with stainless steel bands Correct answer.
  3. Solvent cement applied to the spigot ends
  4. Lead poured into the hub joint

Explanation

No-hub couplings use an elastomeric sleeve, usually neoprene or a similar rubber, held by stainless steel bands tightened to a specified torque so the joint stays flexible and resists shear. Solvent cement does not bond cast iron, and leaded hub joints are a different, older method. Cast iron soil pipe is not threaded in this application.

Question 10Trade Fundamentals, Tools, Materials and Safety

Why must a dielectric union be installed where copper tube connects to a steel pipe?

  1. To allow the joint to be taken apart without a wrench
  2. To break electrical continuity and reduce galvanic corrosion at the joint Correct answer.
  3. To increase the pressure rating of the steel pipe
  4. To prevent thermal expansion of the copper tube

Explanation

Dissimilar metals in contact with an electrolyte form a galvanic cell, and the less noble metal, here the steel, corrodes preferentially. A dielectric union inserts an insulating barrier so the metals are electrically separated while still making a sound pressure-tight joint. It does not raise pressure ratings or absorb expansion.

Question 11Trade Fundamentals, Tools, Materials and Safety

What is the main reason for installing a cleanout at the base of a soil stack?

  1. To measure flow in the drainage system
  2. To give access for clearing a blockage in the building drain Correct answer.
  3. To support the stack above the floor
  4. To vent the stack to the outdoors

Explanation

A cleanout provides a plugged opening through which a drain auger or rod can be introduced to clear a stoppage in the building drain or stack base. Venting is done by the vent stack and its termination, not by a cleanout. Cleanouts carry no flow-measuring or structural function.

Question 12Trade Fundamentals, Tools, Materials and Safety

Which practice best protects a soldered copper joint from failing immediately after assembly?

  1. Reheat the fitting while the solder is still molten
  2. Cool the joint with a wet rag and apply full system pressure at once
  3. Wipe the joint and allow it to cool naturally before pressure testing Correct answer.
  4. Open the nearest valve to flush water through the hot joint

Explanation

Solder needs to solidify and the joint to cool before it is disturbed or pressurised, otherwise the still-molten alloy can crack or be pushed out of the cup. Wiping removes excess solder and flux residue while the joint is warm. Flooding a hot joint with water can quench it unevenly and weaken the bond.

Question 13Trade Fundamentals, Tools, Materials and Safety

A plumber is selecting a hanger for a horizontal run of copper tube. Which requirement should govern the spacing chosen?

  1. The manufacturer's or code-listed support spacing for that tube size and material Correct answer.
  2. The length of the longest ladder on site
  3. The number of fittings in the run
  4. The colour coding of the pipe

Explanation

Support spacing depends on the pipe material, diameter, and the weight of its contents, and it is set by the applicable code or the manufacturer's listings so the pipe does not sag or stress joints. Colour coding identifies services but does not determine spacing. Ladder length and fitting count have no bearing on support intervals.

Question 14Trade Fundamentals, Tools, Materials and Safety

Which tool is used to check that a drainage line falls at the required gradient over a long run?

  1. Laser level Correct answer.
  2. Rotary hammer
  3. Pipe cutter
  4. Micrometer

Explanation

A laser level establishes a consistent reference line or plane so the fall over a long distance can be measured and maintained accurately. A micrometer measures small thicknesses, a rotary hammer drills masonry, and a pipe cutter cuts tube. Gradient is a matter of elevation change over distance, which a levelling device resolves.

Question 15Trade Fundamentals, Tools, Materials and Safety

What is the correct action before using a propane torch to solder inside a basement near a gas-fired water heater?

  1. Close all basement windows to keep the flame steady
  2. Check for and remove ignition sources and ensure adequate ventilation Correct answer.
  3. Open the tank valve fully to clear the area
  4. Cover the water heater with a wet cloth and proceed

Explanation

Open flame near a gas appliance risks igniting accumulated gas or flammable vapours, so ignition sources such as pilot lights are shut off or isolated and the space is ventilated before the torch is lit. Closing windows concentrates fumes instead of removing them. A wet cloth does not isolate a pilot flame or prevent vapour ignition.

Question 16Trade Fundamentals, Tools, Materials and Safety

Which property of a plumbing material makes it suitable for a concealed hot-water line that may freeze in winter?

  1. Resistance to freezing damage combined with temperature rating for hot water Correct answer.
  2. Ability to be threaded
  3. High density compared with steel
  4. High thermal conductivity

Explanation

A material used for hot water in a freeze-prone location must be rated for the service temperature and able to tolerate expansion if its contents freeze. PEX, for example, is rated for hot water and can expand without splitting, unlike rigid materials that may rupture. Conductivity, density, and threadability are not the deciding factors.

Question 17Trade Fundamentals, Tools, Materials and Safety

What does the term developed length mean when calculating the drain size for a fixture?

  1. The depth of the trap seal
  2. The total length measured along the centreline of the pipe including fittings Correct answer.
  3. The length of pipe delivered to site
  4. The straight-line distance between the fixture and the stack

Explanation

Developed length follows the actual path of the pipe, adding the equivalent lengths of bends and fittings, because each fitting adds friction that a straight-line measurement ignores. It is used with the fixture load to size the branch correctly. Delivered pipe length and trap seal depth are unrelated to this calculation.

Question 18Trade Fundamentals, Tools, Materials and Safety

Which statement about the safe use of a ladder while installing pipe near an overhead line is correct?

  1. Two workers may stand on the same ladder to steady it
  2. A ladder may be leaned against the pipe being installed
  3. Non-conductive ladders are preferred and the required clearance from power lines is maintained Correct answer.
  4. Aluminium ladders may be used if the line is insulated

Explanation

Overhead power lines require a maintained clearance, and non-conductive ladders such as fibreglass reduce the risk of contact current. Aluminium conducts electricity and must not be used near live lines regardless of insulation. Leaning a ladder on unsupported pipe or loading it with two people creates fall hazards.

Question 19Trade Fundamentals, Tools, Materials and Safety

Which fitting is used to connect two pipes of different diameters in a straight run?

  1. Tee
  2. Cap
  3. Reducer Correct answer.
  4. Elbow

Explanation

A reducer has one end sized for the larger pipe and the other for the smaller, allowing a straight transition between different diameters. An elbow changes direction, a tee creates a branch, and a cap closes off a pipe end. None of those performs a diameter change in a straight line.

Question 20Trade Fundamentals, Tools, Materials and Safety

A plumber must cut a thread on a steel pipe. Which sequence is correct for a sound, leak-free threaded joint?

  1. Ream the pipe end after assembly to remove burrs
  2. Ream the pipe end, cut the thread, apply jointing compound, and tighten to engage the threads fully Correct answer.
  3. Cut the thread and assemble without reaming or sealing
  4. Cut the thread, apply compound to the male thread, and assemble hand tight only

Explanation

Reaming removes the internal burr that would restrict flow, cutting a tapered thread matches the fitting, and a suitable compound or tape seals the small spiral gap between the threads. Tightening must engage enough threads to develop a seal without splitting the fitting. Skipping reaming or sealing produces restricted flow and leaks, and reaming after assembly is impossible.

Question 21Trade Fundamentals, Tools, Materials and Safety

What is the function of a vent stack in a plumbing drainage system?

  1. To store water for flushing
  2. To carry sewage to the sewer
  3. To admit air so trap seals are not siphoned Correct answer.
  4. To supply potable water to fixtures

Explanation

The vent allows air to enter the drainage system so that pressure in the pipe stays close to atmospheric and the water seal in each trap is not pulled out by siphonage. It carries air, not sewage or water. Water supply and storage are functions of the distribution and tank systems.

Question 22Trade Fundamentals, Tools, Materials and Safety

A plumber is working in a confined space such as a pit and the atmosphere has not been tested. What is the correct approach?

  1. Test the atmosphere and provide ventilation and rescue arrangements before entry Correct answer.
  2. Lower a rope and enter without testing if the pit is shallow
  3. Enter quickly and leave if breathing becomes difficult
  4. Enter with a dust mask and a torch

Explanation

Confined spaces can contain oxygen-deficient or toxic atmospheres that give little warning, so testing, forced ventilation, and a rescue plan are required before entry. Relying on symptoms is dangerous because collapse can occur without warning. A dust mask filters particles only and does not supply oxygen or remove all toxic gases.

Question 23Trade Fundamentals, Tools, Materials and Safety

Which statement correctly compares a compression fitting with a flared fitting on copper tube?

  1. A compression fitting uses a brass ring compressed onto the tube, while a flared fitting uses a cone pressed against a flared tube end Correct answer.
  2. A flared fitting uses a rubber sleeve, while a compression fitting uses solder
  3. Both fittings require the tube end to be threaded
  4. Both fittings are only suitable for plastic pipe

Explanation

A compression fitting seals by crushing a brass or copper olive onto the outside of the tube as the nut is tightened, while a flared fitting seals at a flared cone of the tube pressed against a matching seat. Neither type requires threads on the tube itself. They are mechanical joints for metal tube and do not use solder or rubber sleeves.

Question 24Trade Fundamentals, Tools, Materials and Safety

Why is it important to keep the ends of plastic pipe capped or plugged during storage on site?

  1. To prevent the pipe from rolling
  2. To stop the pipe from changing colour
  3. To keep dirt, debris, and small animals out of the bore Correct answer.
  4. To make the pipe easier to cut

Explanation

Open pipe ends collect soil, grit, and sometimes rodents, and that material can block valves, meters, and small orifices once the system is assembled. Capping the ends keeps the bore clean until installation. The practice has nothing to do with rolling, colour, or ease of cutting.

Question 25Plumbing Fixtures, Fittings and Appliances

Which fixture fitting is installed at the connection between a water closet and its drain to seal the drain opening and prevent sewer gas from entering the bathroom?

  1. A supply stop valve
  2. A floor drain strainer
  3. A water hammer arrestor
  4. A closet flange Correct answer.

Explanation

The closet flange (water closet flange) is fastened to the floor and to the drain pipe, and it receives the closet bolts and the wax ring that seals the fixture outlet. It anchors the water closet and provides the gas-tight joint between fixture and drainage system.

Question 26Plumbing Fixtures, Fittings and Appliances

A lavatory faucet delivers 1.5 gpm at 60 psi. What is the approximate flow rate if the same faucet is supplied at 15 psi, assuming turbulent flow through the aerator and a square-root relationship between pressure and flow?

  1. 1.5 gpm
  2. 0.38 gpm
  3. 0.75 gpm Correct answer.
  4. 3.0 gpm

Explanation

For a fixed orifice with turbulent flow, flow varies as the square root of pressure. Reducing pressure to one quarter (60 to 15 psi) gives a flow multiplier of the square root of 0.25, which is 0.5, so 1.5 gpm becomes about 0.75 gpm.

Question 27Plumbing Fixtures, Fittings and Appliances

In a public restroom, which device is required at each lavatory to prevent backflow from a submerged outlet when the faucet outlet is below the fixture rim?

  1. An air gap or vacuum breaker Correct answer.
  2. A double check valve assembly
  3. A pressure-reducing valve
  4. A thermal expansion tank

Explanation

A submerged faucet outlet creates a cross-connection risk, so an air gap or an approved vacuum breaker is used to break the siphon and protect the potable supply. Double check assemblies and pressure-reducing valves serve different functions and do not provide the required fixture-level protection.

Question 28Plumbing Fixtures, Fittings and Appliances

What is the primary purpose of the trap seal in a plumbing fixture?

  1. To filter debris from the waste flow
  2. To increase drain velocity
  3. To retain a water barrier that blocks sewer gas Correct answer.
  4. To reduce water pressure at the fixture

Explanation

The trap holds a measured depth of water (the trap seal) that blocks sewer gas and odors from entering the building while allowing waste to pass. Trap seal depth and venting requirements are set by code to keep that barrier intact.

Question 29Plumbing Fixtures, Fittings and Appliances

A water closet is rated at 1.28 gallons per flush. How many gallons does it use for 25 flushes?

  1. 64 gallons
  2. 40 gallons
  3. 25 gallons
  4. 32 gallons Correct answer.

Explanation

Multiply the per-flush volume by the number of flushes: 1.28 gallons times 25 equals 32 gallons. This is a straightforward consumption calculation used when comparing high-efficiency fixtures.

Question 30Plumbing Fixtures, Fittings and Appliances

Which condition indicates that a fixture trap has lost its seal?

  1. The fixture drainpipe has a slope greater than required
  2. The fixture drains slowly but has no odor
  3. Sewer odor is present at the fixture and gurgling is heard when nearby fixtures drain Correct answer.
  4. The fixture supply pressure is higher than normal

Explanation

Sewer odor plus gurgling points to a lost trap seal, often caused by siphonage from inadequate venting or by evaporation in an unused fixture. The water barrier is gone, so gas can pass into the room.

Question 31Plumbing Fixtures, Fittings and Appliances

What is the standard function of an air gap in a fixture installation?

  1. To vent the building drain to the outdoors
  2. To separate the potable water supply from the fixture rim by an unobstructed distance Correct answer.
  3. To allow air to enter the drain to speed flow
  4. To balance pressure between hot and cold supplies

Explanation

An air gap is the unobstructed physical distance between a potable water outlet and the flood-level rim of the receiving fixture. That separation prevents backflow by making it impossible for waste to reach the supply.

Question 32Plumbing Fixtures, Fittings and Appliances

A shower valve must limit the maximum delivered water temperature to protect bathers. Which device is designed to do this?

  1. A pressure-balancing valve only
  2. A thermostatic mixing valve Correct answer.
  3. A check valve on the hot supply
  4. A gate valve on the cold supply

Explanation

A thermostatic mixing valve senses outlet temperature and adjusts the hot and cold mix to hold a set maximum, which is the function required for scald protection. A pressure-balancing valve responds to pressure changes but does not directly control temperature to a set limit.

Question 33Plumbing Fixtures, Fittings and Appliances

Which fixture is classified as a water closet in plumbing terminology?

  1. A urinal
  2. A toilet Correct answer.
  3. A bidet
  4. A drinking fountain

Explanation

In plumbing codes and specifications, a water closet is the fixture commonly called a toilet, receiving waste and discharging it through a trap to the drainage system. Urinals, bidets, and drinking fountains are separate fixture categories.

Question 34Plumbing Fixtures, Fittings and Appliances

A flushometer valve on a water closet is chattering and fails to shut off completely. Which condition is the most likely cause?

  1. A missing closet bolt cap
  2. An undersized drain line
  3. A clogged fixture trap
  4. A worn diaphragm or piston in the valve Correct answer.

Explanation

Chattering and failure to seat fully in a flushometer usually trace to a worn or debris-damaged diaphragm or piston inside the valve. The repair is to clean or replace that internal part and verify the supply pressure is adequate.

Question 35Plumbing Fixtures, Fittings and Appliances

What is the minimum required size of a lavatory drain outlet in most plumbing codes for a standard lavatory?

  1. 1 1/4 inches Correct answer.
  2. 2 inches
  3. 1 1/2 inches
  4. 3 inches

Explanation

Standard lavatories are commonly listed with a 1 1/4 inch drain outlet, and the trap and fixture drain are sized to match that outlet. Oversizing the fixture outlet is not required and larger sizes apply to other fixtures.

Question 36Plumbing Fixtures, Fittings and Appliances

A fixture has a drain outlet that discharges into a receptor with a visible gap. What is this arrangement called?

  1. A direct waste connection
  2. A combination waste and vent
  3. An indirect waste connection Correct answer.
  4. A wet vent connection

Explanation

An indirect waste connection discharges fixture waste through an air gap into a receptor rather than piping it directly to the drainage system. This protects the potable supply and the drainage system from contamination in applications such as food service equipment.

Question 37Plumbing Fixtures, Fittings and Appliances

How much water does a 1.6 gpf water closet use for 12 flushes?

  1. 24.0 gallons
  2. 12.0 gallons
  3. 15.2 gallons
  4. 19.2 gallons Correct answer.

Explanation

Multiply the flush volume by the number of flushes: 1.6 gallons times 12 equals 19.2 gallons. Comparing this with a 1.28 gpf fixture shows the savings per flush.

Question 38Plumbing Fixtures, Fittings and Appliances

A drinking fountain is being installed. Which requirement protects the potable water supply at the fixture?

  1. The fountain must be supplied at 80 psi
  2. The fountain must be connected with an air gap or approved backflow preventer Correct answer.
  3. The fountain must have a 2 inch trap
  4. The fountain must drain to a floor drain

Explanation

Drinking fountains and similar potable outlets require an air gap or approved backflow protection so that a submerged or flooded condition cannot contaminate the supply. The other items are not the governing requirement for supply protection.

Question 39Plumbing Fixtures, Fittings and Appliances

Which fixture is designed to receive the discharge of a clothes washer and provide an air break?

  1. A water closet
  2. A standpipe Correct answer.
  3. A laundry sink
  4. A floor drain

Explanation

A washer standpipe receives the flexible hose discharge and holds a trap seal while providing an air break between the hose and the drainage system. A laundry sink may accept indirect waste, but the standpipe is the fixture designated for washer discharge.

Question 40Plumbing Fixtures, Fittings and Appliances

A lavatory drains slowly but the trap is clear. What is the most likely cause?

  1. A partially closed supply stop
  2. A loose closet bolt
  3. A blocked or improperly sloped branch drain Correct answer.
  4. A defective faucet aerator

Explanation

If the trap itself is clear, slow drainage points downstream to a partial blockage or inadequate slope in the branch drain. Supply-side components and closet hardware cannot cause slow drainage.

Question 41Plumbing Fixtures, Fittings and Appliances

What is the purpose of a fixture carrier in a wall-mounted water closet installation?

  1. To supply water to the flushometer
  2. To seal the drain connection
  3. To vent the fixture trap
  4. To support the fixture and transmit the load to the building structure Correct answer.

Explanation

A fixture carrier is a structural fitting that supports a wall-hung fixture and transfers its weight to the building framing or floor. The drain seal and water supply are handled by the flange, gasket, and valve, not the carrier.

Question 42Plumbing Fixtures, Fittings and Appliances

A pressure-balancing shower valve is installed. What does it do when a nearby fixture draws cold water and cold pressure drops?

  1. It shuts off all water to the shower
  2. It maintains the set temperature by mechanically limiting hot water flow until pressures equalize Correct answer.
  3. It drains the trap to prevent overflow
  4. It increases cold water pressure to compensate

Explanation

A pressure-balancing valve senses the pressure difference between hot and cold and moves to restrict the hot side, keeping the mix stable and preventing a sudden temperature spike. It does not boost pressure or shut off the shower.

Question 43Plumbing Fixtures, Fittings and Appliances

Which of the following is a characteristic of a high-efficiency water closet?

  1. It uses 1.28 gallons per flush or less Correct answer.
  2. It must be floor-mounted
  3. It requires a 3 inch drain
  4. It has no trap

Explanation

High-efficiency water closets are defined by flush volume of 1.28 gallons per flush or less while meeting performance standards. Drain size, trap presence, and mounting style are separate design factors.

Question 44Plumbing Fixtures, Fittings and Appliances

A fixture drain has a trap with a 2 inch seal. Which condition can reduce the seal depth below the required minimum?

  1. A larger fixture outlet
  2. Evaporation in a fixture that is rarely used Correct answer.
  3. A higher supply pressure at the faucet
  4. A shorter fixture drain length

Explanation

Evaporation removes water from the trap over time, reducing the seal depth and allowing sewer gas to pass. Siphonage from poor venting is another cause, but supply pressure, outlet size, and drain length do not remove the seal.

Question 45Plumbing Fixtures, Fittings and Appliances

What is the function of a vacuum breaker on a hose bibb?

  1. To drain the hose after use
  2. To regulate the outlet pressure to a set value
  3. To prevent backsiphonage when the hose outlet is submerged Correct answer.
  4. To filter sediment from the supply

Explanation

A hose bibb vacuum breaker admits air when supply pressure drops, breaking the siphon so that contaminated water cannot be drawn back into the potable supply. It does not regulate pressure, filter water, or drain the hose.

Question 46Plumbing Fixtures, Fittings and Appliances

A water closet is installed with a wax ring that is compressed but the fixture rocks slightly. What is the most appropriate corrective action?

  1. Increase the flush volume of the valve
  2. Add shims or grout to stabilize the fixture and reseat the seal Correct answer.
  3. Replace the supply stop
  4. Install a larger trap arm

Explanation

A rocking water closet can break the wax seal and cause leaks, so the fixture must be stabilized with shims or grout and the seal reseated. Supply and drain sizing changes do not address movement of the fixture.

Question 47Plumbing Fixtures, Fittings and Appliances

Which fixture is typically required to have a flush valve rather than a flush tank in a commercial installation?

  1. A drinking fountain
  2. A laundry sink
  3. A residential water closet
  4. A commercial water closet supplied at adequate pressure Correct answer.

Explanation

Commercial water closets are often fitted with flushometer valves because they provide a metered flush using line pressure and are suited to high-use public facilities. Residential closets commonly use tanks, and sinks and fountains do not use flush valves.

Question 48Plumbing Fixtures, Fittings and Appliances

A lavatory faucet aerator is clogged with debris. What is the most likely effect on fixture performance?

  1. Reduced flow at the outlet and possible splashing Correct answer.
  2. A leaking closet flange
  3. Increased flow at the outlet
  4. A lost trap seal

Explanation

A clogged aerator restricts flow and can distort the stream, causing splashing or reduced delivery. It does not increase flow, affect the trap seal, or involve the closet flange.

Question 49Water Supply Systems: Pipes, Fittings and Installation

Which pipe material is most commonly specified for buried cold-water service lines because it resists corrosion and has a long service life?

  1. Galvanised mild steel
  2. Lead
  3. Cast iron
  4. Unplasticised PVC (uPVC) Correct answer.

Explanation

uPVC is widely used for underground cold-water supply because it does not corrode in soil, is lightweight, and has smooth bore giving low friction loss. It is joined by solvent cement or rubber-ring push-fit joints and is rated for cold-water pressures only.

Question 50Water Supply Systems: Pipes, Fittings and Installation

What is the primary purpose of a gate valve in a domestic water supply line?

  1. To reduce water hammer pressure surges
  2. To prevent backflow into the mains
  3. To isolate a section of pipe for maintenance Correct answer.
  4. To regulate flow precisely to a fixture

Explanation

A gate valve uses a wedge-shaped disc that lifts fully clear of the flow path, giving an almost unobstructed bore. Its role is on/off isolation, not fine regulation, so it is fitted where a section must be shut down for repair.