Thanks for the feedback. My valves are pretty old so I'd prefer to change the whole thing. They're beginning to leak on both ends, so I didn't want to replace just part of it.
I should probably clarify on the "lossening" direction. I've got a metal pipe, threaded on both ends. The top goes into the valves (also metal). The bottom goes into a PVC elbow and the rest of the system is all PVC. So now that I think about it, I can't really turn the pipe either way because it may loosen at the valve, but then that would be tightening at the elbow, right?
So is it better to cut the PVC below the elbow, then replace the elbow, change the pipe connecting to the valve to PVC? I haven't done this before, so I wanted to know how tricky this would be. I'd have to shut off my water supply at the main meter so if I screw up, I'm in deep doodoo.
A gardner offered to change the whole thing to automatic and put in the timer for $300, but it's just two valves and a pretty short line to the garage, so I was hesitant to pay that much. Then again, given that I can't shut the water supply to my sprinklers separately, it might not be worth the risk to mess things up.
Any more thoughts? Thanks!