Burst water main - how is water emptied out of a gas main?

they never found out where the metal filings came from in the west of Scotland....

I don?t know the answer but it?s a nightmare for the gas companies.

Until they?ve had access to every gas meter supplied and turned of the gas at the meter they can?t restore the supply. If the meter is indoors and the owner away, they have to dig up the pavement to disconnect the property. Happened in our street a few years ago. Fortunately just a clumsy JCB induced fracture, no water involved.

Tim

Gas dewatering equipment :-)

AIUI, this is an air or nitrogen powered venturi pump that sucks the water out into a water trap.

So is that the real reason that all the houses' gas supplies have to be turned off? Not just for reasons of safety but because the dewatering equipment *requires* a sealed pipe (far end and every branch to a house) in order for it to work? How does it cope with a gas main that may not be completely level and so may retain water in the "troughs"?

The good news is that my parents' gas supply was restored this evening after about 48 hours without heating or cooking - other than the electric fan heater and cooking hob that the gas company *gave* my parents (COVID cleaning and quarantine rules mean that it is more trouble than it is worth to take the equipment back after the gas supply has been restored). And their neighbours who have an electric oven rather than gas said they'd cook a bit extra roast lamb and give it to my parents - community spirit is still alive!

Mum and Dad got talking to the people from the gas company and found that engineers had been brought in from all over the place as, far away as Exeter, and there were vans as far as they eye could see parked all the way along the layby along their road.

Are there ever cases where water gets into a gas main and the pressure of gas forces it out of appliances - eg out of the burners of your gas hob or boiler? ;-)

No, it?s simply because without access to the house, there?s no way of being completely certain that restoring the supply isn?t going to fill the house with gas, possibly from some elderly appliance with a dodgy gas valve.

Turning it off at the meter avoids this risk.

Arguably that risk is very small but our neighbours had their gas supply cut off in he street (as they were away at the time) when we lost our gas supply.

Tim

From the lowest point.

Depends on whether the main is totally flat or not. Often if its an old, ie not one of the new plastic ones, then the best approach seems to be to get as much out as possible then hope it all works. There is probably water in the pipe of an old metal gas pipe due to them mostly being rusted up and the clay acting as the pipe wall. The eventual result round here was about six months down the line the whole main had to be replaced by plastic with the associate disruption to supplies and road traffic, to several months to do it. They attempt to fit the new pipe some way from the old one if its really badly rusted so they can leave supplies on while most of the work is done. Brian

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My understanding is that the pump travels inside the pipe, picking up water as it goes and sending it back down a hose. Hence, it does not require a sealed pipe and is just as effective in an uneven pipe.

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ISTR seeing a picture of that happening, many years ago, but I don't recall the circumstances. It may even have been that somebody connected the cooker to the water pipe by mistake. :-)

NY explained :

Well not a full flow, but I have heard of some water being mixed in with gas at the burner, which can be very dangerous when the flame goes out - especially so where the appliance has no flame failure system.

Our old living room gas fire lacks flame failure, but it was only fitted decades ago as a back-up for those (very) rare occaisions when our CH fails. It has only seen any use for a couple of days, since it was installed.

time that got serviced & condemned then.

Round here they dig a series of holes and expose the old metal gas pipe, then break into it and drag the new yellow 'plastic' stuff through the old pipe. Then they have to dig a hole outside every property and connect to the new pipe.

Not sure how the affected properties manage for the few days that it takes. Maybe they only do it in mid summer ?.

Andrew

When this happned in West Sussex in 1986, people closest to the point where an impact mole plough went through a high pressure gas main after penetrating an adjacent water main, had water squirting out of their gas appliances !

When I was at school it was not unusual for the gas and water taps to get connected together in one of the chemistry labs. The short term effect was that all the bunsen burners went out. Later, the rusted gas pipe under the central "island" bench fractured and the gas ignited in the void under the bench. The bench relocated itself by around a metre after having become airborne.

John