How Do 2-Way Valves Regulate Water Flow in Heating Systems?

[TSN79]

A water based heating system is to be regulated by 2-way valves. How do these work exactly? Do they simply constrict the flow? Isn't it so that if a pipe is constricted, the velocity simply increases to maintain the flow? I mean, flow in must equal flow out.

 

[stewartcs]

A water based heating system is to be regulated by 2-way valves. How do these work exactly? Do they simply constrict the flow? Isn't it so that if a pipe is constricted, the velocity simply increases to maintain the flow? I mean, flow in must equal flow out.

A general two-way valve just acts as stop-flow valve (e.g. solenoid valve). Nothing much to them.

Here is a diagram and a brief description of one:

http://www.omega.com/GREEN/pdf/VALVE_TECH_REF.pdf

CS