Gas Supply & Pipework

What is the purpose of a gas meter?

• ATo reduce the incoming gas pressure to the level the appliances need
• BTo measure gas consumption and allow billing✓
• CDecoration only
• DThe meter has no specific purpose

Answer: Gas meters measure consumption in cubic meters for billing purposes.

What are the main components of a gas supply system?

• AMeter, regulator, pipework, safety devices, and appliances✓
• BJust pipes
• COnly the boiler
• DThe system has no specific components

Answer: Gas supply systems include the meter, pressure regulator, pipework, and safety devices.

What is the function of a gas regulator?

• ATo increase the gas pressure so that the appliance burns at its maximum rate
• BTo maintain constant gas pressure at the correct level for appliances✓
• CTo measure the volume of gas used so that the supplier can raise a bill
• DTo reduce the volume of gas passing through the pipework during peak demand

Answer: Regulators maintain stable, safe gas pressure for appliance operation.

What is the typical pressure in a domestic gas supply?

• AApproximately 21 mbar (2.1 kPa)✓
• BVariable, depending on how many appliances are running at the time
• C500 kPa, the same as the pressure in the distribution main
• D100 kPa

Answer: Domestic gas supply pressure is typically around 20-22 mbar.

What materials can be used for gas pipework in homes?

• ACopper, steel, or MDPE plastic (external only)✓
• BPlastic always
• CAny material at all may be used
• DAny metal pipe

Answer: Domestic gas pipes use copper, steel (often with protective coating), or MDPE plastic outside.

Why is copper preferred for gas pipework?

• AFor its appearance, since exposed copper pipe looks neater in a property
• BCost only
• CAny metal tube of the right bore does the job just as well
• DCorrosion resistance, durability, and ease of jointing✓

Answer: Copper resists corrosion, is durable, and allows reliable soldered joints.

What is the purpose of a gas isolation valve?

• ATo allow safe isolation of the supply for maintenance or emergency✓
• BFor decoration
• CTo increase pressure
• DTo measure gas flow

Answer: Isolation valves allow safe disconnection of gas for repairs or emergencies.

Where should an isolation valve be located?

• AAt the meter for the whole supply, and before each appliance✓
• BOnly at the boiler
• CAnywhere on the pipe
• DOnly outdoors

Answer: Isolation valves should be at the meter and upstream of each appliance for safety.

What is pipe sizing based on?

• AThe appearance of the finished pipe run and how well it can be concealed
• BJust the total length of the run between the meter and the appliance
• CGas pressure, flow rate, and allowable pressure drop✓
• DCost only

Answer: Pipe sizes are calculated based on pressure, flow demand, and acceptable pressure loss.

What is the purpose of a gas pressure test?

• ATo increase the pressure in the pipework so that appliances work harder
• BJust a visual inspection of the joints along the length of the pipe run
• CAn unimportant formality
• DTo verify pipework integrity and ensure no leakage✓

Answer: Pressure testing verifies the integrity of the entire gas system.

What is a typical gas pressure test procedure?

• AEach engineer decides how to test the system, as the procedure is not standardised
• BApplying air or inert gas at specific pressure and monitoring for pressure loss✓
• CFilling the pipework with water and watching for drips at the joints and fittings
• DA visual inspection of the pipework only, with no instrument reading taken at all

Answer: Pressure tests apply air (or inert gas) and measure any pressure loss over time.

What is a tightness test for gas systems?

• AA pressure test checking for a pressure drop over time✓
• BA check that has been dropped from current practice
• CChecking if connections are tight
• DA smoke test to detect gas leaks at joints and connections

Answer: A tightness test is a pressure test, not a smoke test. The installation is pressurised and, after a let-by check and a stabilisation period, the gauge is watched for any pressure drop over the test period. A smoke tracer is not used, and simply feeling whether connections are tight proves nothing.

What type of jointing method is used for copper gas pipes?

• ATwist-on connectors of the type used for low-pressure water pipe
• BSolder (capillary or compression fittings)✓
• CAny method
• DTape wrapping

Answer: Copper pipes use capillary or compression fittings with solder for strong, leak-free joints.

What is a gas leak detector?

• AA chemical or electronic device that detects escaping gas✓
• BA visual inspection of the pipework carried out with a torch and a mirror
• CThe gas meter itself, read before and after the appliance is turned on
• DAn obsolete piece of equipment that engineers no longer carry

Answer: Gas leak detectors (soap solution or electronic) identify leaks from joints and pipes.

What odor does mains gas have?

• ANaturally none; the smell comes from the burner when the appliance runs
• BVaries
• CPleasant smell
• DA strong mercaptan odor added for safety detection✓

Answer: Natural gas is odorless, but mercaptan is added to create a distinctive smell for leak detection.

What is the purpose of a gas meter box?

• AIt is a decorative cover chosen to match the exterior finish of the property
• BIt simply holds the meter in place so that it does not move on the wall
• CThe box serves no purpose
• DProtects the meter and provides safe access for reading and maintenance✓

Answer: Meter boxes protect the meter from weather and physical damage.

Where should a gas meter be located?

• AAny location that suits the property owner, including inside a bedroom cupboard
• BEasily accessible, away from living areas, in a well-ventilated location✓
• CHidden inside the building where it cannot be seen by visitors or callers
• DOutdoors always

Answer: Meters should be easily accessible for reading and maintenance, but not in main living spaces.

During a tightness test on a domestic natural gas installation, the pressure rises after the emergency control valve has been closed. What does that indicate?

• AThe emergency control valve is letting by, so gas is still passing it✓
• BThe installation is sound and the test can be recorded as a pass
• CThe test gauge has been connected to the test point the wrong way round
• DThe pipework has cooled, so the gas inside it has contracted

Answer: A rise in pressure with the emergency control valve closed means gas is still passing the valve, which is known as let-by. The valve has to be proved sound before the test can continue, because gas entering the system would mask a leak. It is a pressure drop, not a rise, that points to a leak in the installation itself.

What should be checked at a gas connection point?

• AOnly the pressure reading taken at the appliance test nipple
• BParticular checks are unnecessary at this point
• CJust the appearance of the joint and whether it has been painted
• DTightness, corrosion, and proper jointing✓

Answer: Gas connections should be checked for tightness, corrosion, and proper assembly.

What is a governor in a gas system?

• AAn official
• BA valve only
• CA device that is not used in domestic work, as it is only fitted to industrial supplies
• DA device that maintains constant gas pressure despite variations in supply pressure✓

Answer: Governors automatically maintain stable outlet pressure regardless of inlet variations.

What is the purpose of a safety relief valve in gas pipework?

• AA minor detail
• BTo increase the pressure in the pipework when demand from appliances is high
• CTo release excess pressure and prevent dangerous over-pressurization✓
• DJust a backup

Answer: Safety relief valves protect the system from over-pressurization.

What is secondary regulation in a gas system?

• AOptional
• BA redundant arrangement
• CMain pressure control
• DReduced pressure regulation near the appliance for final fine-tuning✓

Answer: Secondary regulators fine-tune pressure immediately before appliances.

What materials should NOT be used for gas pipework?

• ACopper
• BSteel with a protective coating, which is not permitted because it corrodes far too quickly
• CAluminum, plastic fittings in pressurized lines, and soft tubing for permanent installation✓
• DMDPE for external use, which is never permitted on any part of a domestic gas installation

Answer: Aluminum, certain plastics, and soft tubing are not suitable for permanent gas installations.

What is the advantage of MDPE (Medium Density Polyethylene) for gas?

• AIt can be used indoors, run inside a wall chase and plastered over once it is installed
• BIts low cost compared with copper tube, which is the only reason that it is chosen
• CIt performs better than copper in every situation, including inside the property
• DFlexibility, corrosion resistance, and ease of installation for external supply✓

Answer: MDPE is flexible, corrosion-resistant, and ideal for external underground gas supplies.

What must be documented when installing a gas system?

• APipe sizes, materials, pressure test results, leakage test results, and appliance details✓
• BOnly the cost
• CRecords are not specified
• DJust the date

Answer: Installation records must document system specifications, tests, and compliance details.