Living in an old house, I have had occasion to have to dash madly down into the cellar and turn off the main water valve when some cobbled together bit of plumbing fails. This caused me to wonder what would happen if the main water valve to the house failed. The water pressure is high enough (60lbs/sq in?) so that it would make taking off the valve and fitting a new one a pretty wet and miserable process. That led me to reflect that the same problem must occur when you tap into the main water line for new construction. I assume you can’t shut down the water for the whole street.
So two questions. 1. In the not unlikely scenario of a disasterous failure in my main water valve, how would a plumber go about replacing it?
In new construction, how do you tap into a water main without everyone getting soaked in the process?
Saw the latter on tv not long ago – there is a special kind of tap that you drill right through the main – better have a permit, eh? – and it seats and seals itself.
I am assuming you are not going to do anything illegal…
Water mains are built like interconnected rings and have shut-off valves that can isolate a whole section, so the workmen can actually work in more-or-less dry conditions.
Where shutting the section off is not possible or not feasible, they have a special type of t-junction that can be fitted over the (intact) main. The t is made in two halves which are fastened with bolts and nuts. Obviously there are all kinds of seal etc to seal the whole thing afterwards. They fit this tee and the rest of the piping. Then it depends on the size of the pipes involved and the pressure. Big pipes/high pressure: they fit a special shut-off valve and drill a tiny hole through the mains pipe (drilling mecahism goes through the shut-off valve) then they wait for the chamber made by the stem of the t and the shut-off valve to fill and the pressures to equalize, then drill away the rest of the mains pipe wall in the t, then open the shut-off valve. Sometimes the t is welded into place after the new section is “live” to strengthen the seal etc. Small pipes: The tee has an integral punch that can cut into the mains pipe sidewall by turning a nut that sits around the stem of the t.
I think a rupture in your service line is more likely. Mine ruptured after 55 yrs.
I had something like this happen to my old house. The main supply line running from the main at the street into my house ruptured and a geyser shot up from a few feet underground. I had the city turn off my supply at the street, then had a plumber dig out the service line and repair it (replaced a section of it to curve around a huge tree). He had a special tool like a cane to turn the main on and off.
The positive and negative water is carried in separate pipes - you have to make sure you connect them the right way around, unless you have alternating water, in whcih case it doesn’t matter so much.
[sub](I wouldn’t have done this if the question hadn’t already been informatively answered)[/sub]