monoflow and butterfly valves

Herb_2

How can I be sure that I am dealing with a forced-circulation system and not a gravity flow system? Does a gravity-flow system ever have any kind of pump located close to the furnace?

Herb_2

flow-control and butterfly valves

I am replacing two small radiatiors supplied by a two-pipe system (one supply,one return). The pipes are one-inch in diameter to within four feet of each radiator, where the pipe is reduced to half-inch. I have been told to install a flow-control valve at each point where the pipe is reduced, although the existing system has no such devices. Questions: 1. Are such valves necessary and how do they operate? 2. Where exactly do I place these valves--before the T (on the 1" pipe), or after the T (on the 1/2" pipe)? 3. Would there be any advantage to reducing the pipe in stages (from 1" to 3/4" to 1/2"), as opposed to going directly from 1" to 1/2"? Many thanks for your service!

Herb_2

dialectric unions

I live in an area where plumbers often run copper pipe directly into galvanized pipe, without using dialectric unions. I have been monitoring such joints for the past twenty years, and have found little or no evidence of corrosion. Questions: 1. Should I still use dialectric unions (in this case, for radiator piping)? 2. If I used brass nipples betweeen the galvanized and copper material, would this retard corrosion? Many thanks!