First the main or leg is disconnected at source, capped off and made safe. If the meter is removed, it should be capped and made safe also.

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The final end of the main or leg should be identified. A thorough investigation of site should be carried out to identify additional branches from the main and a simple line diagram created for reference and volume calculations.

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The purge point end is connected to the purge point shown above by flexible hose. The source of the main is connected to a Purge Fan and operatives use 2 Way Radio to communicate.

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When the fan is turned on, fresh air is forced down the main which begins to purge the gas from the pipe. The gas flows out of the main into the flexible hose, through the purge rig and into the atmosphere. A special flare point is used to prevent flash backs should the gas be ignited.

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An analyser and volume flow meter connected in line to the flare point shows the volume of gas / air purged from the main and the level of gas in the purging mixture. When the calculated volume is purged, and the mixture reads only oxygen, the main is purged and can safely be removed.

A special procedure applies to mains with branches to ensure that 100% of the gas is safely removed from all legs of the pipework.

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