plumbingvalvewater-pressure
I closed the main water valve for simple repairs. After reopening it there's barely any water doesn't even register in the meter. The valve doesn't feel broken but I can't think of what could be wrong.
The solution:
Our main shutoff valve is a small gate valve. We had the city show up and shutoff the water to the house while the plumber replaced the main valve. Apparently it was a bad valve since everything is in working order now.
Without a picture I am guessing, but it sounds like the "something connected above the air valve" is your pressure vacuum breaker. A pressure vacuum breaker prevents water from flowing from the outside back into your main water line (and then into your drinking water). It will allow water from inside your water main to travel through it with the water pressure from your house forcing open the pressure vacuum breaker (while water traveling in the reverse direction closes the valve and prevents contamination of your drinking water).
It does sound like the sprinkler water main has a very slow leak. And I imagine a slow leak from your sprinkler water main is not enough to completely open the pressure vacuum breaker and it is just exiting at this point (when the air valve is closed).
You need to find the main shut off valve in the road, side walk or somewhere on or near your property. They are usually placed in mini manholes with easy access:
But if you're unlucky you will need to get some building plans and try to find where on the plans the supply pipe runs and find the valve at the connection point to the main supply. In most cases it will be near the connection point of the main supply:
but if its not, or if you struggle to close it call your council to help you. You don't want to break that!
It is easy to snap these valves- if its rusted badly apply (known as WD-40, LN-40, HT-40) spray oil based rust release (spray leave an hour try again.. repeat a few times), TAP the valve with a hammer (!TAP!, do not whack it, to help release the valve. Also, usually opening the valve slightly helps to release it then try to close it.
Best Answer
I'm going to assume it's a typical gate valve, and also since you said main water valve I'll assume it's the main shutoff just before the meter.
With these assumptions in mind, I'm going to say you will have to call your local municipality. The water company does not allow (or like) home owners to tamper with anything near (and defiantly not before) the water meter.
In fact, in lots of areas the municipality actually owns the pipe (and any fixtures) before the water meter. So this is not likely a DIY job.
When you call to have them come fix the valve, ask them to replace the broken gate valve with a ball valve.
If I have assumed incorrectly and the valve is on your side of the water meter, you can try to repair it yourself (see this question for how to do it) or you could just replace the broken valve.
If you are going to fix the valve yourself (it's on your side of the meter) and there is no other shut off before this valve, you will have to make a call to the municipality to have the water shut off to the building.
If you do the work yourself, you may have to get a permit and/or have your work inspected by a licensed plumber.