In my plumbing system there is a connection from the main to the sprinkler valve system. The connection is a copper slip to male thread into a pvc female to slip. About every two years the copper gets a pinhole above the threaded section and leaks. Does any one know why this happens and how to correct it. Most houses I have lived in have had copper for years without any problem like this.

Thanks for any help.

, Sounds like you have electrolysis. This is decomposition caused by improper grounding. In other words it eats holes in copper pipe. To repair you must first cut out the faulty places and replace with good pipe. This is done with copper pipe and two couplings, one of which will be a slip coupling. Some solder experience is needed here. Plumbers putty just won't cut it. Next you need to ground out your water supply system. To test, take a AC voltmeter and test both hot and cold lines back to common ground. There should be no reading, even on the smallest setting. I would sugest calling in a plumber to repair your lines and then ask him if he has has experience with electrolysis. If he has he can ground and test it out. If not call in a electrician to finish up. This will only get worse if you let it go. Your pipes are getting ate up 24/7. In the end it can weaken your pipes so much you will have to repipe the house. Hope this explains what is happening and thank you for rating my reply. TOM