ACS Pipework & Meters 1 — Questions and Answers
Question 1: What colour is the MDPE (medium density polyethylene) gas service pipe used underground in Great Britain?
- Black
- Yellow (Correct answer)
- Blue
- Orange
Correct answer: Yellow
Yellow MDPE is the standard colour for gas service pipes installed underground in the UK, distinguishing them from other buried utilities (blue for water, black for electricity).
Question 2: What is the function of the Emergency Control Valve (ECV) on a gas installation?
- To regulate gas pressure at the meter
- To isolate the entire gas supply to a property in an emergency, located immediately upstream of or adjacent to the gas meter (Correct answer)
- To control the gas flow to individual appliances
- To reduce the gas supply to a safe pressure from the mains
Correct answer: To isolate the entire gas supply to a property in an emergency, located immediately upstream of or adjacent to the gas meter
The ECV (quarter-turn cock) is the master isolation valve for the property's gas supply, used in emergencies to cut off all gas and by engineers before carrying out gas work.
Question 3: Which type of fitting is used to join copper gas pipework in domestic installations and does NOT require soldering?
- Solder-ring fittings
- Compression fittings or press-fit fittings (Correct answer)
- Brazed fittings
- Welded couplings
Correct answer: Compression fittings or press-fit fittings
Compression fittings and press-fit fittings mechanically join copper pipe without heat, reducing fire risk during installation and making them suitable for use in occupied buildings.
Question 4: What is the purpose of a gas meter index reading?
- To verify that the gas pressure is correct
- To record the volume of gas consumed at the premises, forming the basis of the customer's gas bill (Correct answer)
- To measure the efficiency of the gas appliance
- To confirm the meter is correctly calibrated by the engineer
Correct answer: To record the volume of gas consumed at the premises, forming the basis of the customer's gas bill
The meter index records cumulative gas consumption (in cubic metres or cubic feet); billing is based on the difference between successive readings multiplied by the calorific value of the gas.
Question 5: What does 'pipe sizing' involve when designing a domestic gas installation?
- Selecting the correct colour of pipe to use in each location
- Calculating the correct pipe diameter to supply the required gas flow rate to all appliances simultaneously without excessive pressure drop (Correct answer)
- Measuring the length of pipe needed for ordering purposes only
- Selecting pipe based on the age of the property
Correct answer: Calculating the correct pipe diameter to supply the required gas flow rate to all appliances simultaneously without excessive pressure drop
Pipe sizing uses gas rate demand, pipe length, number of fittings, and permissible pressure drop tables (BS 6891) to select pipe diameters that ensure adequate gas pressure at all appliances under simultaneous load.
Question 6: What does the term 'standing pressure' mean in gas supply measurement?
- The pressure measured when all appliances are running at maximum demand
- The gas pressure measured at a test point with no appliances operating (static condition) (Correct answer)
- The pressure required to lift the gas from the main to the meter
- The pressure at which the safety valve opens
Correct answer: The gas pressure measured at a test point with no appliances operating (static condition)
Standing (static) pressure is measured with no gas flowing; working (dynamic) pressure is measured with appliances running — comparing the two reveals pressure drop across the installation under load.
ACS Pipework & Meters 1
What colour is the MDPE (medium density polyethylene) gas service pipe used underground in Great Britain?