ACS Tightness Testing & Purging 1 — Questions and Answers
Question 1: Which instrument is typically used to perform a tightness test on a domestic gas installation?
- Electronic combustible gas detector
- U-gauge manometer (Correct answer)
- Digital pressure data logger
- Rotary gas meter
Correct answer: U-gauge manometer
A U-gauge manometer is used because it can detect very small pressure changes that would indicate a gas escape from the installation.
Question 2: At what pressure should a tightness test be conducted on a domestic natural gas installation?
- 75 mbar
- 50 mbar
- Working pressure (approximately 21 mbar) (Correct answer)
- 100 mbar
Correct answer: Working pressure (approximately 21 mbar)
Tightness tests are performed at working pressure (approximately 21 mbar for natural gas) to replicate actual operating conditions.
Question 3: How long should the final tightness test period last after stabilisation for a standard domestic installation?
- 30 seconds
- 1 minute
- 2 minutes (Correct answer)
- 5 minutes
Correct answer: 2 minutes
The final test period is 2 minutes after the stabilisation period, as specified in IGEM/UP/1B for standard domestic installations.
Question 4: What constitutes a satisfactory result during a domestic gas tightness test?
- A pressure drop of no more than 2 mbar
- A pressure drop of no more than 4 mbar
- No pressure drop at all (Correct answer)
- A pressure drop of no more than 1 mbar
Correct answer: No pressure drop at all
A satisfactory tightness test requires zero pressure drop, as any fall in pressure indicates gas is escaping from the installation.
Question 5: What is the purpose of the stabilisation period before the final tightness test reading is taken?
- To allow gas to escape to a safe background level
- To allow temperature and pressure to equalise (Correct answer)
- To allow the meter to begin recording gas flow
- To allow the U-gauge fluid to reach ambient temperature
Correct answer: To allow temperature and pressure to equalise
The stabilisation period allows temperature-related pressure fluctuations to settle so that accurate and reliable readings can be taken.
Question 6: What position should all appliance isolation valves be in during a tightness test?
- Open, to test the full installation including appliances
- Closed, isolating all appliances from the pipework (Correct answer)
- Half-open to allow controlled gas flow
- Dependent on the type of appliance being tested
Correct answer: Closed, isolating all appliances from the pipework
All appliance isolation valves must be closed so the tightness test checks the integrity of the pipework only, not the internal components of appliances.
Question 7: Which of the following would indicate a failed tightness test?
- The U-gauge reading remains completely stable throughout the test
- The gas pressure rises slightly during the test period
- The U-gauge shows a pressure drop during the test period (Correct answer)
- The meter registers no flow during the test
Correct answer: The U-gauge shows a pressure drop during the test period
A pressure drop on the U-gauge during the test period indicates gas is escaping from the installation, meaning the tightness test has failed.
ACS Tightness Testing & Purging 1
Which instrument is typically used to perform a tightness test on a domestic gas installation?