Imperial valves with 24VAC coils will easily overload modern controllers, unless you use something heavy-duty like a Hunter ICC. Imperial controllers used a 50 VA transformer, more than twice the capacity of the 20 VA transformers used with most entry-level controllers of today.Only seen 1 valve that was not complatible, that was a 110v system, ever other valve has worked fine some were as old as 30 years old