Harold Kestenholz
A flow control valve is a weighted check valve that has enough weight on the check to prevent gravity flow, but is light enough not to interfere with the force of the pump. Before Star-Trek, the flow control valve could have been called an anti-gravity-flow check valve; it seems too techie to call it that now. Another difference between a check valve and a flow control is that there is a handle or screw to open the check in the flow control valve. There is no handle in most check valves to do that.
When there is more than one circulator pumping outward to separate zones, the flow control valve does work as a check valve.
A problem can occur in replacing a flow control valve with a check valve. A boiler that is kept hot, such as a boiler with a tankless coil, will create enough gravity flow to keep a check valve open providing unwanted heat in circulator zones. In this situation, flow control valves are required.
Zones controlled with zone valves do not need a flow control except when someone wants to keep the hot boiler water of a tankless coil boiler away from zone valves on the supply side.
You can see the difference in piping arrangements in the free design lessons section of http://www.hydronic.net
