Let's imagine the following situation. Something happened to the cold water tap, and it urgently needs to be replaced with a new one. At the same time, there is no way to turn off the riser through utilities. This often happens on weekends. What to do in such a situation? You can, of course, wait, but you can do everything yourself. The most important thing is to sensibly assess the risks and prospects of such an event, as well as be ready to take responsibility if "everything goes wrong."
Having finished with the warning rhetoric that plumbing repair, especially "extreme", should be undertaken only if you have skillful hands, understanding the issue, and if you have at least minimal skills in this area, we will move on to describing the technology of replacing a ball valve under pressure … As you might have guessed, the main problem of such an adventure is not so much in the water as in the pressure under which it will escape. The work is long and laborious. Changing the tap under the stream and doing insulation will definitely not work.
But you can try the following. Attach a piece of garden hose to the new ball valve using the adapter. Its end will be sent to the sink, bathtub or toilet (which will be closer to the place of work). The bottom line is that immediately after removing the old tap, put a new one on the edge so that the stream of water goes down the drain. Water will continue to drain along the thread, however, at least it will be possible to work with the pipe.
While the water is flowing, we take a metal brush and clean the threads with it from the old seals. After that, we wind hermetic and tow on the existing part of the thread. Now you can turn on the valve to the end and check its tightness.
Important: you need to prepare the workplace. Put a bucket under the pipe, get hold of a few rags and remove everything unnecessary and interfering around.
Want even more interesting things about plumbing? How about we figure it out why there are no cleaning brushes in American toilets and what is dictated by it.