In general, a zone valve is an exact type of valve that is used to manage the flow of water stream for a hydronic heating or cooling process. To enhance efficiency, these systems are generally divided into several zones. Here is an example, in an apartment; a floor can be served by a heating zone while the third and fourth bedrooms can be served by using another. This is the process by which the heat is can be transferred to the floors in the daytime and mainly to the bedrooms in the nighttime

Various return zone valves are available but one of the popular and most used options is Erie return zone valves. The features and specification of Erie return valves are:

SKU: VT2313G13A020
UPC: 071142662548
Weight: 2.00 LBS

Great discounts are offered by various companies when bought in bulk.

Zone valves are also a part of a home hydronic system and need electricity to be powered. The zone valves are managed by low-voltage thermostats and are connected by low-voltage wiring. These valves can also be made using wax motors and a spring-return technology. In this case, the valve generally gets closed by the force of the spring and can be again opened by wax motor force.

For more details: http://www.mychillyair.com/erie-vt2313g13a020-24v-3-4-sweat-2-position-spring-return-zone-valve/