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Operating a U gauge and digital manometer
Gas Tightness Testing Procedure (Domestic UK)
The test is conducted by a Gas Safe-registered engineer following industry standards (typically IGEM/UP/1B).
Preparation: All appliances must be turned off, isolation valves closed, and the area well-ventilated. The manometer is connected to the test point on the gas meter.
Let-By Test: The system is briefly pressurised to 7-10 mbar. The emergency control valve (ECV) is then closed, and the gauge is monitored for one minute to ensure no pressure rise, which would indicate a faulty ECV.
Stabilisation: After a successful let-by test, the pressure is raised to 20 mbar (for natural gas; 37 mbar for LPG) and allowed to stabilise for one minute to account for temperature and pressure changes.
Tightness Test: The pressure is monitored for a further one to two minutes (depending on system volume). Any pressure drop indicates a leak.
Assessment: The observed pressure drop is compared against permissible limits, which vary depending on the meter type and pipework diameter. New installations must have no pressure drop at all.
Check list for tightness testing
Task:
Carry out a domestic test for tightness on an existing gas installation with existing appliances
Installed. Ensure installation is left gas tight or within the tolerances permitted
Preparation
Visually examine the installation before carrying out the test
Check appliances isolation valves are all in the open position
Check all appliance control taps are “off”
Lifted any fold down cooker lids
Visually checked condition of “ U gauge manometer and rubber tube
Zeroed U Gauge manometer correctly
Turn off gas supply at ECV
Removed test nipple & connected pressure gauge
Let By Test
Slowly raised gas pressure to 7 – 10 MBR
Turned off gas supply at ECV
Observed gauge for 1 min
Temperature stabilisation test:
Slowly raised pressure to 20 MBR (note water level)
Turn off gas supply at ECV
Observed gauge for 1 minute
Actual Tightness Test:
Ensure pressure still at 20 MBR
Observed gauge for 2 minutes noting any pressure drop
Completion of tightness test:
Remove gauge and replace test nipple screw
Turn on gas supply at ECV
Used leak detection (LDF) on test nipple screw and wiped dry
Tools and equipment For the Tasks
Temporary Continuity Bonding Clamps
A temporary continuity bond is a mandatory 1.2-meter, 10mm squared flexible copper cable with heavy-duty crocodile clips used by gas engineers. It maintains electrical continuity across a gas meter during disconnection or reconnection to prevent electric shock or ignition from earth leakage, as meters often have insulating, non-conductive components.
Key Aspects of Temporary Continuity Bonding
Safety Function: Prevents the risk of arc ignition, fire, or electric shock if the pipework becomes live when breaking continuity during meter removal or pipe repair.
Usage: Applied before the meter is removed. One clip is attached to the upstream (service) pipe and the other to the downstream (installation) pipe, maintaining electrical continuity between them.
Specifications: Commonly, a 1.2m to 1.4 m long, 10mm squared flexible copper cable is used. They are often rated for at least 250 v and high amperage, with insulated crocodile clips for safety.
Compliance: Essential for meeting Gas Safety Regulations and standards such as BS 6891.
Procedure: Once the bond is securely attached to both sides, the meter can be safely removed and the pipes capped.
Essential Tightness Test Equipment:
Manometer / U-Gauge: The primary tool, used in liquid (water) form (e.g., Monument or Regin U-gauge) or digital form (e.g., Kane, Testo, TPI 608) to measure pressure in millibars (mbar).
Leak Detection Fluid (LDF) / Spray: Used to pinpoint leaks at joints by spraying, ensuring compliance with BS EN 14291.
Pressure Testing Pump / Bulb: Used to pressurize the system, especially for air testing and finding leaks (e.g., Rothenberger or TPI pumps).
Test Nipples / Adaptors: Used to connect the manometer to the meter test point.
Gas Analyser (Optional): Some electronic analyzers can perform tightness tests, though not a replacement for a manometer.
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