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WBBSE Madhyamik Vocational Plumbing study materials
WBBSE Madhyamik Vocational Plumbing study resources

WBBSE Madhyamik Vocational Plumbing practice questions

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Question 1Introduction to Plumbing Trade, Tools, and Safety

In the plumbing trade, which material is most commonly used for manufacturing wash basin taps because it resists corrosion and is easy to chrome-plate?

  1. Cast iron
  2. Asbestos cement
  3. Brass Correct answer.
  4. Galvanised steel

Explanation

Brass is an alloy of copper and zinc that resists corrosion well and takes a smooth chrome finish, which is why most domestic taps and fittings are made from it. Cast iron, steel and cement products are used for pipes or drainage, not for tap bodies.

Question 2Introduction to Plumbing Trade, Tools, and Safety

A plumber needs to cut an internal thread inside a GI pipe socket. Which tool is designed for this operation?

  1. Spirit level
  2. Pipe cutter
  3. Die stock with die head Correct answer.
  4. Pipe wrench

Explanation

A die stock holds a die head whose hardened internal cutting teeth form an external thread on a pipe; the matching tap forms internal threads. A pipe wrench grips and turns, a cutter severs the pipe, and a level checks alignment, so none of them cuts threads.

Question 3Introduction to Plumbing Trade, Tools, and Safety

Before starting work on a pipeline, why should a plumber close the main stop valve and open a downstream tap?

  1. To increase water pressure in the line
  2. To test the color of the water supply
  3. To drain residual water and confirm the supply is actually isolated Correct answer.
  4. To lubricate the valve spindle

Explanation

Closing the stop valve isolates the section, and opening a downstream tap releases trapped water so the pipe can be worked on dry. It also proves the isolation is effective, because water would keep flowing if the wrong valve had been closed.

Question 4Introduction to Plumbing Trade, Tools, and Safety

Which personal protective equipment is most important when a plumber is cutting a threaded pipe with a hacksaw and metal chips may fly?

  1. Safety goggles Correct answer.
  2. Ear muffs
  3. Rubber apron
  4. Cotton gloves

Explanation

Safety goggles shield the eyes from flying metal chips and dust, which are the main hazard in hacksaw cutting. Aprons protect clothing, ear muffs guard hearing, and gloves protect hands, but none of these protects the eyes from a chip strike.

Question 5Introduction to Plumbing Trade, Tools, and Safety

What is the main purpose of a trap fitted below a wash basin?

  1. To filter out sand from the water supply
  2. To increase the flow rate of the drain
  3. To reduce the noise of flowing water
  4. To store a water seal that blocks sewer gases from entering the room Correct answer.

Explanation

A trap retains a small body of water called the water seal, and this seal stops foul gases and odours from the drainage system from entering the building. It does not boost flow, filter supply water, or serve mainly as a silencer.

Question 6Introduction to Plumbing Trade, Tools, and Safety

Which of the following is a correct safe practice when using a pipe wrench on a steel pipe?

  1. Oil the jaws heavily so they slip smoothly
  2. Pull the handle towards the body for better control
  3. Fit an extension pipe on the handle to increase leverage
  4. Stand clear of the swing and pull the handle away from the body Correct answer.

Explanation

A pipe wrench can slip suddenly when force is applied, so the handle should be pulled away from the body and the worker should stay clear of the swing path. This prevents hand and knuckle injuries if the jaws lose grip.

Question 7Introduction to Plumbing Trade, Tools, and Safety

A plumber has to bend a 15 mm copper tube without kinking it. Which method is appropriate?

  1. Hammer the tube over a sharp edge
  2. Heat the tube to red hot and twist it by hand
  3. Use a spring bender or a lever-type tube bender Correct answer.
  4. Fill the tube with sand and strike it with a mallet

Explanation

A bending spring or a lever bender supports the tube wall and produces a smooth bend of controlled radius without flattening the cross-section. Hammering or twisting by hand collapses the tube and restricts flow.

Question 8Introduction to Plumbing Trade, Tools, and Safety

Why is galvanised iron pipe preferred over bare steel pipe for conveying cold water in a building?

  1. The zinc coating increases the internal diameter
  2. Galvanising makes the pipe lighter than plastic
  3. Galvanised pipe needs no jointing material
  4. The zinc coating protects the steel from rust and prolongs its life Correct answer.

Explanation

Galvanising deposits a zinc layer that shields the underlying steel from moisture and oxygen, so the pipe corrodes far more slowly than bare steel. The coating does not change weight, bore, or the need for proper joints.

Question 9Introduction to Plumbing Trade, Tools, and Safety

A plumber is fixing a leaking joint in a live water line inside a building. Which sequence of steps is safest and most correct?

  1. Increase the pump pressure to identify the crack
  2. Repair the joint while water is flowing to locate the leak
  3. Close the nearest isolating valve, drain the line, then repair the joint Correct answer.
  4. Dismantle the joint first, then search for the stop valve

Explanation

The line must be isolated and drained before a joint is opened, otherwise water sprays out and the repair cannot be made properly. Working on a pressurised line also risks scalding and flooding.

Question 10Introduction to Plumbing Trade, Tools, and Safety

What does the term 'water seal' refer to in a sanitary trap?

  1. The valve that closes the water supply to a cistern
  2. The rubber gasket fitted between the WC pan and the floor
  3. The cement mortar used around a drain pipe
  4. The depth of water retained in the trap that blocks foul gas Correct answer.

Explanation

The water seal is the vertical depth of water held in the trap bend, and this depth must be maintained to stop sewer gas passing into the room. Gaskets, mortar and supply valves serve entirely different functions.

Question 11Introduction to Plumbing Trade, Tools, and Safety

Which tool would a plumber select to check whether a newly laid horizontal drain pipe has the required fall?

  1. Plumb bob
  2. Micrometer
  3. Spirit level Correct answer.
  4. Vice

Explanation

A spirit level with its bubble in the vial shows whether the pipe is level or sloping, and the gradient can be checked by comparing levels over a known length. A plumb bob checks verticality, a micrometer measures thickness, and a vice holds work.

Question 12Introduction to Plumbing Trade, Tools, and Safety

Why should a plumber avoid joining copper pipe directly to galvanised steel pipe without a dielectric coupling?

  1. Dissimilar metals in contact with water cause galvanic corrosion Correct answer.
  2. Copper is always softer than steel
  3. The two metals have different colours
  4. The joint cannot be threaded

Explanation

When copper and galvanised steel touch in the presence of water, a small galvanic cell forms and the less noble zinc coating corrodes rapidly, leading to leaks. A dielectric coupling breaks the metallic contact and prevents this.

Question 13Introduction to Plumbing Trade, Tools, and Safety

A plumber needs to hold a pipe firmly on a workbench while filing a thread. Which workshop tool is most suitable?

  1. Stillson wrench
  2. Pipe cutter
  3. Bench vice Correct answer.
  4. Caulking tool

Explanation

A bench vice clamps the workpiece between its jaws so both hands are free for filing and threading. Wrenches turn fittings, cutters sever pipe, and caulking tools lead joints, so none of them holds work securely on a bench.

Question 14Introduction to Plumbing Trade, Tools, and Safety

Which of these is the correct reason for fitting an air gap or an anti-siphon device on a cistern inlet?

  1. To reduce the noise of the inlet valve
  2. To measure the water level in the cistern
  3. To increase the filling speed of the cistern
  4. To prevent backflow of contaminated water into the supply main Correct answer.

Explanation

An air gap or anti-siphon arrangement stops water from being drawn backwards into the potable supply if pressure drops, which protects the main from contamination. It does not speed filling, silence the valve, or measure level.

Question 15Introduction to Plumbing Trade, Tools, and Safety

During excavation for an underground drainage line, why must the trench sides be sloped or supported?

  1. To make the pipe look straighter
  2. To allow rainwater to collect at the bottom
  3. To reduce the amount of bedding sand used
  4. To prevent soil collapse that could bury workers Correct answer.

Explanation

Loose soil in a deep trench can collapse suddenly and trap or suffocate a worker, so the sides are battered back or shored with timber. This is a basic excavation safety requirement on drainage work.

Question 16Introduction to Plumbing Trade, Tools, and Safety

What is the function of a stop cock in a domestic water supply system?

  1. To filter suspended particles from the water
  2. To measure the quantity of water used
  3. To release air trapped in the pipeline
  4. To regulate the flow of water and shut off the supply to a section Correct answer.

Explanation

A stop cock is a manually operated valve that can throttle or completely close the supply so that a section of piping can be isolated for repair. It is not a meter, a filter, or an air release valve.

Question 17Introduction to Plumbing Trade, Tools, and Safety

A plumber is selecting a pipe for a hot water line operating at about 80 degrees Celsius. Why is ordinary PVC pipe unsuitable for this duty?

  1. PVC reacts with oxygen in the water
  2. PVC cannot be joined with solvent cement
  3. PVC softens and loses strength at elevated temperature Correct answer.
  4. PVC is heavier than copper

Explanation

Unplasticised PVC softens as temperature rises and loses pressure strength, so it is limited to cold water service. Hot water lines need materials such as CPVC, PPR, or copper that retain strength at high temperature.

Question 18Introduction to Plumbing Trade, Tools, and Safety

In a multi-storey building, a plumber observes that water is being siphoned out of traps on the lower floors whenever the upper floor discharges. Which condition best explains this?

  1. The supply pressure is too high
  2. Inadequate venting causes pressure fluctuations in the drainage stack Correct answer.
  3. The pipe gradient is too steep in the branch drain
  4. The traps are too deep and hold excess water

Explanation

Without adequate vent pipes, the slug of water falling down the stack creates a partial vacuum behind it, and this negative pressure sucks the water seal out of the lower traps. Proper venting equalises pressure and preserves the seals.

Question 19Introduction to Plumbing Trade, Tools, and Safety

A plumber measures the internal diameter of a pipe as 25 mm and its wall thickness as 3 mm. What is the approximate outside diameter of the pipe?

  1. 31 mm Correct answer.
  2. 28 mm
  3. 22 mm
  4. 25 mm

Explanation

The outside diameter equals the internal (bore) diameter plus twice the wall thickness, because the wall occurs on both sides. Here 25 mm plus 2 times 3 mm gives 31 mm.

Question 20Introduction to Plumbing Trade, Tools, and Safety

A plumber is asked to recommend the most suitable jointing method for buried cast iron soil pipe that must remain flexible against ground movement. Which choice is best?

  1. A rubber ring or gasket push-fit joint Correct answer.
  2. Molten lead caulked into the socket
  3. Solvent cement applied to the spigot
  4. Threading the spigot into the socket

Explanation

A rubber ring joint compresses inside the socket and allows slight angular movement and settlement without cracking the pipe, which suits buried soil lines. Rigid methods transmit ground movement and are more likely to fail.

Question 21Plumbing Materials, Pipes, Fittings, and Joints

In WBBSE vocational plumbing terminology, what does the 'bore' of a GI pipe refer to?

  1. The internal diameter of the pipe through which water flows Correct answer.
  2. The thickness of the galvanised zinc coating
  3. The external diameter measured across the socket
  4. The length of the threaded portion at each end

Explanation

Bore is the nominal internal diameter that determines the flow-carrying capacity of a pipe. Pipe sizes such as 15 mm, 20 mm and 25 mm are quoted as nominal bore, not as the outside diameter or coating thickness. This is why two pipes with the same bore may differ in wall thickness and outside diameter.

Question 22Plumbing Materials, Pipes, Fittings, and Joints

Which material is most commonly used for underground soil and waste drainage pipes because it resists chemical attack from sewage?

  1. Copper
  2. Galvanised mild steel
  3. Cast iron with bitumen coating
  4. Unplasticised polyvinyl chloride (UPVC) Correct answer.

Explanation

UPVC is chemically inert to most sewage constituents and is light, smooth-bored and easy to joint with solvent cement. Its smooth bore also reduces the chance of solids settling. Galvanised steel and copper are costly and corrode in aggressive sewage, while cast iron is heavy and subject to internal corrosion over long periods.

Question 23Plumbing Materials, Pipes, Fittings, and Joints

A plumber needs to join two 25 mm GI pipes permanently in a straight run in a wall chase. Which fitting is designed for this purpose?

  1. Reducer
  2. Union
  3. Cap
  4. Socket (coupling) Correct answer.

Explanation

A socket, also called a coupling, is a short threaded sleeve that joins two pipes of the same nominal bore in a straight line. A union is used where the joint must be opened later for maintenance. A reducer changes bore, and a cap closes off a pipe end.

Question 24Plumbing Materials, Pipes, Fittings, and Joints

Which of the following is a characteristic property of chlorinated polyvinyl chloride (CPVC) that makes it suitable for hot water lines?

  1. It can withstand sustained temperatures around 90 degrees Celsius Correct answer.
  2. It is a metallic alloy of copper and zinc
  3. It is completely rigid and cannot be bent
  4. It requires lead-based solder for jointing

Explanation

Extra chlorine atoms in the CPVC polymer chain raise its softening temperature, so it can carry hot water at roughly 80 to 95 degrees Celsius depending on pressure rating. Ordinary PVC softens at much lower temperatures and is limited to cold water and drainage. CPVC is jointed with solvent cement, not solder.

Question 25Plumbing Materials, Pipes, Fittings, and Joints

What is the main purpose of applying solvent cement to PVC pipe and fitting surfaces before assembly?

  1. To seal the joint against water pressure only by mechanical compression
  2. To lubricate the surfaces so the pipe slides in easily
  3. To soften the surfaces so they fuse into a single continuous joint Correct answer.
  4. To provide a heat-resistant barrier around the joint

Explanation

Solvent cement dissolves the surface layer of both PVC parts, and as the solvent evaporates the softened material fuses into one continuous mass. This produces a joint stronger than the pipe wall itself. It is not a lubricant, a simple gasket seal or a heat barrier.

Question 26Plumbing Materials, Pipes, Fittings, and Joints

Which type of valve is best suited for isolating a branch line so that it is either fully open or fully closed, and is not intended for throttling flow?

  1. Gate valve Correct answer.
  2. Needle valve
  3. Pressure reducing valve
  4. Globe valve

Explanation

A gate valve uses a wedge-shaped disc that lifts fully out of the flow path, giving almost no resistance when open. It is meant for on-off isolation, and partly open positions cause disc vibration and wear. Globe and needle valves are designed for throttling, and a pressure reducing valve controls downstream pressure rather than acting as an isolator.

Question 27Plumbing Materials, Pipes, Fittings, and Joints

In a threaded GI pipe joint, why is white lead or PTFE tape applied to the male thread before screwing into a fitting?

  1. To conduct heat away from the joint during tightening
  2. To prevent the pipe from rusting on the outside
  3. To increase the diameter of the thread so it grips more tightly
  4. To fill the spiral gap between mating threads and prevent leakage Correct answer.

Explanation

Threaded joints leak along the helical clearance between the male and female threads. A sealing compound such as white lead paste or PTFE tape fills that spiral gap and is squeezed into it as the fitting is tightened. It is not a diameter-increasing device, an external rust barrier or a heat conductor.

Question 28Plumbing Materials, Pipes, Fittings, and Joints

What does the nominal size '15 mm' on a GI pipe sold in the market indicate?

  1. The exact outside diameter of the pipe
  2. The length of one standard pipe section
  3. The nominal bore, close to the internal diameter Correct answer.
  4. The maximum working pressure in bar

Explanation

GI pipe sizes such as 15 mm and 20 mm are nominal bore designations that approximate the internal diameter. The actual outside diameter is larger because wall thickness is added. Length of a standard section is usually about 6 m, and pressure rating is a separate specification.

Question 29Plumbing Materials, Pipes, Fittings, and Joints

A plumber must join a 32 mm GI pipe to a 20 mm GI pipe in a straight run. Which fitting is required?

  1. Equal socket
  2. Nipple
  3. Bend
  4. Reducer socket Correct answer.

Explanation

A reducer socket has one end threaded for the larger bore and the other for the smaller bore, so it makes a straight transition between the two sizes. An equal socket joins pipes of the same bore, a bend changes direction, and a nipple is a short threaded piece joining two fittings of the same size.

Question 30Plumbing Materials, Pipes, Fittings, and Joints

Which statement correctly distinguishes a tee from a cross in GI fittings?

  1. A tee reduces the bore while a cross keeps it equal
  2. A tee is used only for drainage while a cross is used only for water supply
  3. A tee has one branch outlet while a cross has two branch outlets Correct answer.
  4. A tee changes direction by 90 degrees while a cross changes it by 45 degrees

Explanation

A tee has a single branch at right angles to the main run, giving three openings, while a cross has two opposite branches, giving four openings. Bore reduction and use in supply or drainage are independent of whether the fitting is a tee or a cross. Bends, not tees, are the fittings that change the direction of a run.

Question 31Plumbing Materials, Pipes, Fittings, and Joints

A 25 mm GI pipe is to be cut and threaded on site. Which sequence of operations is correct?

  1. Cut to length, thread the pipe, then hammer the end flat
  2. Cut to length, ream the bore, then cut threads with a die Correct answer.
  3. Ream the bore, thread the pipe, then cut to length
  4. Thread first, then cut to length, then ream the ends

Explanation

The pipe is first cut square to the required length, then the internal burr is removed with a reamer so the bore is clear and the die can start evenly. Threads are cut afterwards with a pipe die of the correct size. Threading before cutting would leave the thread damaged by the cut and would make length control difficult.

Question 32Plumbing Materials, Pipes, Fittings, and Joints

Why should a PVC drainage pipe be provided with a solvent-cemented joint rather than a threaded joint?

  1. Threading thin PVC wall reduces strength and creates stress concentrations, so solvent welding is preferred Correct answer.
  2. Threaded PVC joints are not permitted in any plumbing installation
  3. Solvent cement joints can be dismantled easily for cleaning
  4. PVC threads cannot be cut because the material is too hard

Explanation

Cutting threads into a thin thermoplastic wall removes material and creates sharp notches where cracks start under load or thermal movement. Solvent cement fuses the full wall thickness and gives a stronger, leak-tight joint. Threaded plastic joints do exist for some fittings but are not the normal choice for drainage pipe runs.

Question 33Plumbing Materials, Pipes, Fittings, and Joints

Which fitting is used at the base of a vertical soil stack to change direction from vertical to horizontal while easing the flow of solids?

  1. Sanitary tee Correct answer.
  2. Vent cap
  3. Floor drain
  4. P-trap

Explanation

A sanitary tee has a curved branch that guides flow smoothly from the vertical stack into the horizontal drain, reducing the chance of blockage. A vent cap terminates the vent pipe on the roof, a P-trap holds a water seal, and a floor drain is a receptor, not a direction-changing fitting.

Question 34Plumbing Materials, Pipes, Fittings, and Joints

What is the function of a 'bib cock' in a domestic water supply installation?

  1. To control the entire supply to the building
  2. To draw water from a supply line at a tap point, usually with a screwed nose for a hose Correct answer.
  3. To reduce water pressure before it enters the geyser
  4. To prevent backflow into the main supply

Explanation

A bib cock is a small draw-off tap fitted at the end of a supply branch, commonly with a screwed nose for attaching a hose. The main building control is a stop cock, backflow prevention is done by a non-return valve, and pressure reduction is done by a pressure reducing valve. Each of these is a distinct fitting with a distinct function.

Question 35Plumbing Materials, Pipes, Fittings, and Joints

A plumber is installing a hot water line and a cold water line close together in a concealed wall. Which material combination is most appropriate?

  1. Copper for hot water and asbestos cement for cold water
  2. PVC for hot water and CPVC for cold water
  3. GI for hot water and lead for cold water
  4. CPVC for hot water and PVC for cold water Correct answer.

Explanation

CPVC withstands the higher temperature of hot water, while ordinary PVC is adequate and cheaper for cold water. Reversing them would cause the PVC hot line to soften and deform. Lead and asbestos cement are health hazards and are no longer acceptable for potable water lines.

Question 36Plumbing Materials, Pipes, Fittings, and Joints

Which of the following best explains why copper pipes are often joined with capillary solder fittings rather than threaded fittings?

  1. Copper is too soft to be threaded reliably, and capillary soldering gives a strong leak-tight joint with minimal wall reduction Correct answer.
  2. Copper cannot be cut with a hacksaw, so only soldered joints are possible
  3. Threaded copper fittings are illegal in all countries
  4. Solder joints allow the pipe to be dismantled easily for repair

Explanation

Copper is a relatively soft metal, and cutting threads into thin-wall copper tube weakens it and is difficult to seal. Capillary soldering draws molten solder into the annular gap by capillary action, producing a strong joint without removing wall material. Soldered joints are permanent, not demountable.

Question 37Plumbing Materials, Pipes, Fittings, and Joints

In a GI water supply line, what is the purpose of a 'union' fitting?

  1. To join two pipes of different bores permanently
  2. To change the direction of the pipeline by 90 degrees
  3. To close the end of a pipe during pressure testing
  4. To provide a demountable joint that can be opened for maintenance without cutting the pipe Correct answer.

Explanation

A union consists of three parts, with a nut and a ground brass or rubber seat, allowing the joint to be unscrewed and remade repeatedly. This is useful at valves, meters and appliances. Reducing is done by a reducer, direction change by an elbow, and end closure by a plug or cap.

Question 38Plumbing Materials, Pipes, Fittings, and Joints

Which property of cast iron makes it a traditional choice for soil and waste pipes in large buildings?

  1. High compressive strength and good sound insulation Correct answer.
  2. Low weight and easy handling by a single worker
  3. Ability to be solvent-welded to plastic fittings
  4. Complete resistance to internal corrosion

Explanation

Cast iron has high compressive strength and its dense wall damps the noise of flowing waste, which is valued in large buildings. It is heavy and requires two workers or lifting gear, it corrodes internally over time, and it cannot be solvent-welded to plastic. Joints are made with caulked lead, rubber gaskets or mechanical couplings.

Question 39Plumbing Materials, Pipes, Fittings, and Joints

A water supply line shows a persistent leak at a threaded GI joint even after tightening. Which is the most likely cause?

  1. The thread is damaged, cross-threaded or insufficiently engaged Correct answer.
  2. The pipe is installed vertically rather than horizontally
  3. The zinc coating is too thick
  4. The pipe bore is too small for the flow

Explanation

Leakage at a threaded joint usually comes from damaged, crossed or short threads that prevent proper engagement and sealing. The remedy is to remake the joint with new thread and fresh sealant. Bore size, coating thickness and pipe orientation do not cause leaks at a threaded joint.

Question 40Plumbing Materials, Pipes, Fittings, and Joints

Which of the following correctly describes the difference between a 'coupling' and a 'reducing coupling' in plastic drainage fittings?

  1. A coupling changes direction, while a reducing coupling does not
  2. A coupling joins pipes of different diameters, while a reducing coupling joins pipes of the same diameter
  3. A coupling is used only for hot water, while a reducing coupling is used only for cold water
  4. A coupling joins pipes of the same diameter, while a reducing coupling joins pipes of different diameters Correct answer.

Explanation

A coupling is a straight sleeve used to join two pipes of the same nominal diameter, and a reducing coupling has one socket sized larger than the other to step down the pipe size. Temperature service and direction change are unrelated to the coupling versus reducing coupling distinction.

Question 41Plumbing Materials, Pipes, Fittings, and Joints

In a plumbing installation, what is the primary purpose of a 'P-trap'?

  1. To retain a water seal that prevents sewer gases from entering the building Correct answer.
  2. To increase the flow velocity in the drain
  3. To reduce the noise of flowing water in the stack
  4. To filter out solid waste before it reaches the drain

Explanation

The U-shaped bend of a P-trap holds a plug of water that blocks sewer gas from travelling back into the building. It does not accelerate flow, filter solids or provide acoustic insulation. The water seal must be maintained by regular use or by a trap primer.

Question 42Plumbing Materials, Pipes, Fittings, and Joints

A plumber finds that a newly solvent-welded PVC joint leaks under test pressure. Which is the most probable cause?

  1. The pipe colour was grey rather than white
  2. The pipe was cut with a hacksaw and not reamed
  3. The cement was applied only to the pipe and not to the fitting socket, or the joint was disturbed before curing Correct answer.
  4. The pipe was stored horizontally before installation

Explanation

Solvent welding requires cement on both the pipe end and the fitting socket, and the joint must be held undisturbed while the solvent evaporates and the plastic fuses. Missing cement on one surface or movement during curing leaves an incomplete weld that leaks. Cutting method and pipe colour do not cause leakage by themselves.

Question 43Plumbing Materials, Pipes, Fittings, and Joints

Why is a dielectric union used where a copper pipe connects to a GI pipe?

  1. To increase the flow rate through the connection
  2. To allow the joint to be opened for cleaning
  3. To break electrical continuity and prevent galvanic corrosion at the dissimilar metal joint Correct answer.
  4. To reduce the water pressure at the connection

Explanation

When copper and galvanised steel are in contact in the presence of water, a galvanic cell forms and the less noble zinc coating corrodes rapidly. A dielectric union inserts an insulating sleeve and washer to break metallic contact, preventing that galvanic action. It does not regulate pressure or flow, and demountability is a secondary feature.

Question 44Plumbing Materials, Pipes, Fittings, and Joints

A plumber must install a branch connection in a horizontal UPVC drainage line where the branch enters at 45 degrees to the direction of flow. Which fitting is correct?

  1. Sanitary tee with a 90 degree branch
  2. Straight coupling
  3. Test tee
  4. Wye (Y) branch fitting Correct answer.

Explanation

A wye branch has its outlet at about 45 degrees to the main run, which gives a smoother flow path for solids entering the branch. A 90 degree sanitary tee would create a sharper turn and a greater blockage risk on a horizontal line. A coupling has no branch, and a test tee is for pressure testing access.

Question 45Plumbing Materials, Pipes, Fittings, and Joints

Which combination of pipe material and jointing method is correctly matched for a concealed hot water line in a modern building?

  1. PVC pipe with lead caulking
  2. GI pipe with solvent cement
  3. Cast iron pipe with capillary soldering
  4. CPVC pipe with solvent cement Correct answer.

Explanation

CPVC is a thermoplastic rated for hot water and is jointed with solvent cement appropriate for CPVC. GI pipe is jointed with threads, PVC is not rated for hot water, and cast iron is jointed by caulking or mechanical couplings, not soldering. Only the CPVC pairing is both technically valid and suitable for the duty.

Question 46Plumbing Materials, Pipes, Fittings, and Joints

A plumber needs a fitting to connect two lengths of 20 mm UPVC water-supply pipe in a straight line, with no change of direction and no reduction in bore. Which fitting is appropriate?

  1. A 20 mm UPVC socket (coupling) Correct answer.
  2. A 20 mm UPVC tee
  3. A 20 mm UPVC end cap
  4. A 20 mm UPVC elbow

Explanation

A socket, also called a coupling, has two plain sockets in line and simply joins two pipes of the same diameter in a straight run. It does not alter the direction or the bore of the line. Elbows, tees and caps all change either the direction, the number of outlets or the termination of the pipeline.

Question 47Plumbing Materials, Pipes, Fittings, and Joints

In a building drainage system, a 110 mm UPVC soil pipe is to be joined to a 75 mm UPVC branch pipe in a straight line. Which fitting should be used?

  1. A 110 mm × 75 mm UPVC reducer (reducing coupling) Correct answer.
  2. A 75 mm UPVC elbow
  3. A 110 mm UPVC socket
  4. A 110 mm UPVC door bend

Explanation

Whenever two pipes of different diameters are joined in a straight line, a reducer or reducing coupling is needed because it has one socket sized for the larger pipe and one for the smaller. A plain socket only joins pipes of the same nominal size. Elbows and bends change direction and do not solve a diameter mismatch.

Question 48Plumbing Materials, Pipes, Fittings, and Joints

A plumber is making a threaded joint between two GI pipes using a socket, and the pipes must be removable later for maintenance. Which arrangement gives a sound, serviceable joint?

  1. Apply PTFE tape to the male threads, screw both pipes into the socket and tighten with pipe wrenches Correct answer.
  2. Use solvent cement on the threads before screwing the pipes in
  3. Fit the socket with the threads left bare and rely on the taper to seal
  4. Weld the socket to both pipe ends after cutting square threads

Explanation

GI pipe joints seal because the tapered male thread wedges into the tapered female thread, and a thread sealant such as PTFE tape fills the spiral gap between them. Screwing both pipes into a socket with wrenches produces a pressure-tight joint that can still be unscrewed later. Welding or cementing would make the joint permanent and is not the method used for GI screwed fittings.

Question 49Plumbing Materials, Pipes, Fittings, and Joints

A plumber has to connect a copper tube to a GI pipe in a domestic water line. Which jointing arrangement is most suitable?

  1. Join them with a compression fitting on the copper side and a screwed fitting on the GI side, using a dielectric union between the two metals Correct answer.
  2. Braze the copper tube directly into the GI pipe end
  3. Clamp the two pipes together with a rubber hose and jubilee clips
  4. Screw the copper tube directly into a GI socket using PTFE tape

Explanation

Copper and galvanised steel are dissimilar metals, so direct contact in the presence of water sets up galvanic corrosion that eats away the less noble metal. A dielectric union places an insulating barrier between the two materials while still allowing each side to be joined by its own normal method. Compression fittings suit copper and screwed fittings suit GI, so each metal is worked to its own standard.

Question 50Plumbing Materials, Pipes, Fittings, and Joints

A plumber is selecting pipe material for the exposed rainwater downpipe of a small building. The pipe must resist sunlight, be light in weight, and be joined quickly on site without threading. Which material and jointing method best meets these requirements?

  1. Copper tube joined with capillary solder fittings
  2. Cast iron pipe joined with lead-caulked sockets
  3. GI pipe joined with screwed sockets
  4. UPVC pipe joined with solvent cement Correct answer.

Explanation

UPVC is light, rot-proof and unaffected by normal rainwater, and it is assembled quickly with solvent cement, which softens the surfaces so they fuse into a continuous joint. It needs no threading equipment and no molten metal on site. The other options are heavier or need hot work or special machinery, which is unnecessary for a simple rainwater downpipe.