I had someone come over my house and winterize the sprinklers. He explained to me what he did: He said he closed the main valve to the sprinkler system, hooked up a compressor and blew out all the water from sprinkler pipes. He also, opened up the air valve so air can go in but water can not. After that I noticed the water is leaking slowly from the air valve. I called the same guy again and he told me the water is leaking because the main valve to sprinkler system is bad and I need to replace the same.
Can someone please point out if water is leaking from the air valve while the main sprinkler valve is closed, does it need to be replaced. Please note that while the air valve was in the closed position and main sprinkler valve open, no water leaked. Also, while keeping the main sprinkler valve closed, if I close the air valve too, water starts coming out of something connected above the air valve.
Best Answer
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).