I have a 1 inch water supply line coming into an apartment building. It then hits a shutoff valve and then water meter and then takes a 90 degree bend going up. It then hits something that I am not sure what it is and I am trying to figure it out. It is a brass colored fitting with a handle. After that it hits a water pressure regulator valve (which I just had to replace and got me to start to think about what this other thing it). I'd like to know what it is for my own knowledge and also because I'd like to add another water shutoff valve to the main line coming into the building in case the primary shutoff leaks or stops working for some reason. However, I am not sure if this thing in question is a shutoff valve or not. I am posting some pictures of it here. If it is a shut off valve I wasn't able to figure out how to use it to shut off the water on the supply line.
