What is this thing that is leaking?

I'm a newbie here - enjoy reading and learning from everyone. I have a 15 year old home. I noticed that on the main water line coming into my utility room I have a slow leak. It's coming from something that is shaped like an inverted foam coffee cup with a screw portruding from the top. I assume it's something to moderate water presssure...is that right? Will it need to be replaced? It's held in place with 4 bolts and appears to be leaking from the joint between the top part and base part, also looks like there might be a gasket between these parts - if that's correct, can I just replace the gasket? I also would guess that I need to have the water turned off at the street in order to work on this. Thanks for any help.

You are correct. That is a pressure reducing valve. The valve should be located after your meter and main shut off valve. Thus, you should not have to turn the water off at the street to service the pressure reducing valve. However, if you do not have a functioning shut off valve, then you will have to have the water turned off at the street. Perhaps you can replace the gasket, but a new valve will likely be less than $100 so I expect most people would just replace the valve rather than mess with the gasket. Good luck.

Thanks for the quick reply! I should have asked this question as well - is this something I can do? I know I can replace it, but does it need to be calibrated for the correct pressure? Do these things come with instructions or does a 'real plumber' need to get involved? I'm very handy around the house and am not afraid to try these things. Thanks again.

It should not be too tough. The valve will probably come preset to a certain pressure, maybe 50 or 60 psi, but most are adjustable within a range. There will be a screw on the top that controls the pressure. I would install it out of the box and see how your pressure is. If you need more, open the screw a bit.

You can also obtain a pressure gauge for under $10 that will attach to any hose bib you have in your house. This will tell you what your static water pressure is. You should check with the city water department to see what pressure you main carries, you may not even need a pressure reducer. They should be able to give you that information on the telephone.

Thanks again for the good info!

Where I am (about 1/4 mile from a pumping station) the pressure is 125 psi. No one uses a pressure reducer.