I said it wasn't professional. It could save him a bunch of money. He said he has a Rain Dial. It'll easily handle it. So what if the controller stops working down the road? He's gonna replace it anyway. Obviously he'll have to choose two lines that are compatible. I didn't mention that. I figured he was smart enough to test to see which two can run at the same time. He could just abandon one of the valves and hook the pipes up together. I've never had a controller go bad from hooking two solenoids together. If I can run two valves at the same time and save an elderly person who's on a limited income some money. I'll do it.
I must admit that I don't have near the practical experience as mrfixit here. I'm speaking from sort of a lawyer perspective and making sure we don't do anything that could void the warrantee of a controller that isn't cheap.
But is sounds like mrfixit's practical experience is envoking my caviot of "verify a zone on the controller can handle the current draw required of the two valves".
When I tried to look into the specification, here's what I could find: An Irritrol Rain-Dial series specifys a Maximum output per station of 0.5 amps. So I looked at the specs for a few Rainbird valves. I would generalize the Rainbird specifications has having an inrush current of 0.3 amps and a holding current of 0.23 for residential valves and an inrush current of 0.41 amps and a holding current of 0.28 amps for commercial valves.
If valves similar to the Rainbird residential valves are being used, then the holding current for two valves is just below Rain-Dail maximum specification and the inrush current only exceeds the max by 20%.
If valves similar to the Rainbird commercial valves are being used, the the holding current for two valves is just an itty bitty bit above the Rain-Dail maximum, but the inrush current exceeds the max by as much as 64%.
So if valves similar to the Rainbird residential are being used, then I would agree that they are unlikely to seriously damage a Rain-Dial controler since we only exceed the maximum by only 20% and only during the brief initial inrush (and that's if the valves happen to be on the high end of the spec, Rain-bird quotes thes as max values, so real world values might be even smaller).
But if valves similar to the Rainbird commercial valves are being used, pushing the max output during operation and blowing by it by more than 60% during the inrush would worry me.