I need to do some work on valves that have a slow leak. When shutting down the water, I noticed the main valve to shut the water down needs repair/replacement. I’m afraid to turn the handle as it may leak. Before having the town shut the water down, I want to make sure I’m ready to replace and don’t have leaks after. There are two pieces of copper pipe that screw into the valve. Those two pieces of pipe have a nut that screw them down. See below. My plan is to simply unscrew the two nuts, unscrew the two pipes (elbow piece and straight piece) from the valve, replace valve, screw in two pieces, tighten down the nuts. Done. Based on images below, does that seem correct? Is there a better way? Should I be putting tape on the two areas screwed down with the nuts? If not tape, should they be dry? Or? Any words of wisdom? Thanks.

 

The valve looks to be a 3/4" threaded valve. I'd replace it with a ball valve like this one: (you can get one anywhere)
https://www.supplyhouse.com/Bluefin-...alve-Lead-Free

There's no waterflow direction, but make sure you install it so the valve can be turned on/off (since it's close to the wall).

The threaded fittings that go into this valve do need to be lubricated/sealed. I always use 3-4 wraps of teflon tape followed by a coating of pipe dope. Both aren't necessary, but I find it to be an easy way to make a solid connection every time.

The union nuts (against the wall and into the water meter) are unions and do NOT need any pipe dope or teflon tape. Just make sure the mating faces are clean before reassembling.

Lastly, make sure you have large slip joint pliers or a 12" or so pipe wrench. You'll need to tighten down the threaded connections tightly before reassembling the unions.


While you're at it, if there's another valve on the other side of the meter, I'd replace it at the same time.

 

You say you have a slow leak. There are two ways that valve can leak. How is yours leaking?

Easiest to fix is if water comes out around the valve stem (it's what's causing the green corrosion). More work is if the valve doesn't completely shut off the flow of water when it's in the off position.

 

Thank you both. I have a water filter that has not been changed in some time. In order to change it, there are several different shut off faucets that need to be closed. One started dripping when I tried to turn it. I started looking around and see several valves/faucet style that have corrosion and appear to have slow leaks. They should be addressed when I am dealing with the one I see dripping. I figured the main water valve would be needed to shutoff to address multiple green leaky valves and the one I saw dripping. But the main is the image in this thread and I didn’t even want to attempt to turn it, in case it started leaking. So step one for me.. get the main so I can shut down easily and confidently. Then deal with the others when the main is good.

I picked up some mega lock and plan to put that and Teflon in the threads (non union parts). Assume that is a reasonable item for this task?

the actual leaky faucet is the lowest red handle. It’s dripping in the vicinity of the red handle.

 

So, you have multiple leaking valves, leaking from different locations. The ones leaking from the valve stem are easy to fix and you don't even have to turn off the water. The leaking valve with compression fittings can be a real bugger to get to seal, especially if it's been leaking for along time.

"I picked up some mega lock and plan to put that and Teflon in the threads (non union parts). Assume that is a reasonable item for this task?"
I don't know what your plan is. There are no fittings that seal by the threads in your photos. You will need valve packing material for the ones leaking from the valve stem. The compression fitting valve may need to be replaced. You can try tightening it a bit more but after it's leaked that long it might not seal and could need to be replaced.