Below is the incoming supply line from the municipal water. I noticed that the shut-off valve is very slowly leaking at the [???] shaft of the knob that turns (almost exactly where the point of the yellow arrow indicates)
My question - Let's say it's time to replace it. How does one do that? I know of no other way to shut off the incoming water.
This is the shutoff valve for your "house" not your residence.
So before this the city has their main shut-off in the front yard (98% of the time) and then probably an outside hose bib (90% of the time) and then this shutoff that shuts off everything inside your house.
You can always call the water company and ask them. But most companies will not replace this for you. Some do it as a service and some have contractors (reduced rates) they will point you to for house shut-off. These screw shutoffs fail all of the time and my water company will actually replace it for you for $25 or free if you are an old lady as they normally come out to turn off the main during this anyway. That isn't normal though so either call and hope for best, call a plumber ($100 if it isn't urgent) or try to replace yourself (have to shut off main to do this).
The stem packing is leaking, a standard repair. Try tightening the bronze hex nut . If that does not stop it, turn off the water , back off the hex nut to get more/new packing on the stem . I used several wraps of teflon tape pipe dope, works well although not approved by every one . I got the idea from an old guy in refinery maintenance. You may need to remove the red handle to lift the hex nut.
The homes in a neighborhood where I used to live, all built in the early 1950s, have no street-side shut-off valves that are accessible without digging up the street. Between jack hammers, laborers, city permits and re-paving, it costs thousands of dollars to access the street-side shut-off valve.
When the main shut-off valve in my basement failed (it no longer shut off the water completely), I opted to freeze the copper water main in my basement where it came up out of a sump in the basement floor. Freezing a short, straight length of soft copper pipe does not cause the pipe to burst. I made sure there was no water flowing anywhere in the house during the freezing process.
I built a gallon-sized cup around the water main about a foot below the bad valve by cutting up an old bleach bottle and reinforced it with duct tape. I filled the cup with pellets of dry ice and wrapped the whole thing in a towel.
After about an hour, the water main had an ice plug in it (evidenced by lack of flow when I opened a nearby faucet) and I cut the threaded brass pipe above the shut-off and installed a brass union and a new full-flow ball valve above the bad valve, leaving the old valve in place in the interest of finishing the job quickly, before the ice plug melted.
This is how licensed plumbers do it in that area, so as crazy as it may sound, it's the accepted practice.
The packing (5) is under the nut (4) on top of the valve body (12) where it seals between the stem (7) and valve body.
When the valve is closed you can bleed the pressure above the seat (9) by opening a valve, e.g. a faucet, inside the house, then closing it. After that you can remove the nut to access the packing with only minor dribbling from water above the valve inside the house. Do NOT open the shutoff valve while the packing nut is removed.
Clean up the stem so that it will seal more reliably, repack the valve, replace the nut and you'll be good to go.
