what are you calling the water main. Is the water main the valve? If so yes the water would stop flowing if you change the diaphragm. You can shut off the water supply to the irrigation vales and keep it off for 2 or more days and see if it starts to dry out. Here is a link that might be useful: leaking_valve

what happens is your trying to move a volume of water at a certain psi through a smaller connection which will lower it's psi thru friction loss but will increase it's velocity thru that same pipe. so what happens is the water hits the fittings or valve at a higher speed causing the hammer to be stronger.

what it sounds like is a blockage on the inbound side of the valve. I would assume the valve is seperated from the other valves of the system since no others are affected. what I suggest is taking the valve apart and flushing the lines. if that doesn't clear the trouble it may be necessary to probe or dig up the line back to the blockage.

This really worked for my Miele G24710. Unbelievable Saved me an $800 repair or the purchase of a new dishwasher. Thank you ilbagnodgiorgio. ilbagnodigiorgio 3 years ago You won't believe this easy solution for a stuck water intake valve that was suggested by Miele. Remove the plastic cover to the valve under the sink. If you can feel the solenoid vibrating when it's attempting to open the valve, you may be in luck. Take a hammer and hit the casing. Yes, hit it hard. After about ten raps, the stuck valve should dislodge itself. This procedure actually worked for me after experiencing the problem with a one year old dishwasher. After three years, it became stuck again. I used the same procedure and it still cleared the problem. Try this before replacing the valve. And don't be afraid to hit it hard.