Differences between these hydronic devices

Hello:

Can someone explain to me the differences between a differential bypass valve, which is supposed to unite the ends of the main supply and return pipes, in a multi zoned hydronic system using baseboard as the emitters throughout the house, and the use
of balancing valves, which are installed at the return side of each of the zones.

From what I'm understanding they serve the same purpose, to make sure the proper pressure is being applied to each of the zones, depending on whether one or more zones are opened/closed.

Are both types of devices intended to coexist together on the same system, or do you use one or the other.

Thanks,
Amado

They both do the same thing in different ways. A differential bypass valve changes it's flow rate as the system flow rate changes while balancing valves just stay in one position. so let's complicate the whole thing and add a variable speed pump to the system LOL. If you have one, of either you don't need the other.

What I've read says that if you have a variable circulator, instead of a fixed one, then the differential bypass valve (or balance valve) is not needed, as it effectively does the same thing. So in the end, either three will accomplish the same thing. Thanks.

Balancing valves are to equalize the rate of flow through the various units. A "bypass valve" allows water to circulate through the system when all the "zone valves" are closed and the pump is running, preventing a "dead head" situation.

Each zone or loop is rarely exactly the same in length or head. When they are all open, the water will flow through the one with the least resistance. To balance the flow so that each zone or loop gets the heat it needs, you may often need a valve to restrict the flow of the one getting the most heat so that the more restrictive ones can get their share. IOW, you probably need balancing valves. If there's the possibility that the pump doesn't like the higher head when not all the zones are open, then you may need either the variable speed circulator or a by-pass valve to keep the flow moving at a sufficient rate. The exact design of your system would dictate whether you need any of these things.

Jim D:

How do you determine if, in your own words "the pump doesn't like the higher head when not all the zones are open"?

Thanks,
Amado

If you have a primary/secondary loop system at the boiler, it probably won't be an issue. The problem can come when the burner is on and the water is moving slowly because only one or a few zones are open, restricting the flow. Then, the aquastat in the boiler might sense the water is getting to the proper temp because it can heat faster than the zone absorbs it, and shut off early. It could end up short-cycling. While it doesn't happen all that much, the pump might become noisy if it is trying to push a lot more water than the open zones would allow. A bypass valve or proper control to adjust a variable speed circulator might be needed, but again, can't say from afar. One of the pros would likely have a thought or two...