How will the plumber stop gas coming out of the supply pipe while he is assembling the elbow to go through the wall to the external control valve.
Really??
Yes really. When my meter was moved the plastic supply pipe was squeezed flat to reduce gas flow to almost zero before the pipe was cut away from the valve and meter. Even outdoors and the pipe squashed flat the smell of gas was noticeable.
How will the gas pipe be closed off between the time it is disconnected from the existing valve and meter and the time is connected to the new pipework. Since the supply pipe in internal it is unlikely to be plastic and therefore could not be closed off by being squashed flat.
Even if the supply pipe is plugged within seconds of being disconnected the amount of gas that escapes could, in a confined space, create a fire or explosion hazard.