Let's Get The Water Back In The Boiler!

ISTR that shows up in Lost Art someplace, but I don't have mine handy- @DanHolohan ?

Not so sure they pressurize the return lines — but they do equalize pressure between them and the headeer (which is where they look like they are going — not to a return). When the zone valves close, if they weren't there you could have much lower pressure in the returns downstream holding the water up against the boiler pressure.

If you are running a system with crossover traps and dry returns, then when the zone valve closes the crossover trap for that main will open very quickly and the main and dry return will equalize at dry return pressure. That works for pressure, but you do need drips — ideally one on each side of the zone valve. This all works provided the steam pressure is low enough that the water can't back out of the cold return into either the main or the return through the drip.

I can easily see how, if the boier pressure is higher, however, the water could be raised as high as the main if the main and boiler weren't equalized. I'd need to see the rest of the piping and know the boiler pressure, though, to see if my guess was any better than speculation..

Counterflow or parallel flow?

I had zone valves on a 2 pipe system in a school that was to be demoed in a few years.

I adjusted the gates to not fully close thinking that this would keep the supply pipe from going into a vacuum and not returning water. It seemed to work OK for a hack job.

"What ever works in a fight" Marquis of Queensbury rules only get you so far sometimes 😉...The longer I do this, the more unconventional solutions join the conventional ones in the 🧰 toolbox. Mad Dog

I think the copper tubing is there to drain the water in front of the zone valve so they don't hammer when they open.

I'd would have made it NOT look like a sloppy add on, or after thought. I wonder if the tube just went from one side of the valve to the other would have worked just as well, using a lot less tubing and not as sloppy. They probably just went with the easiest places to drill the holes.

I am going to have to dig through my files. I had a one pipe system I wanted to zone and worked out a way to get it to work properly. I think I ran it past Denny Molloy and it passed. IIRC you have to run an equalizer down from the supply on the system side of the zone valve to the wet return from that zone and then run the return over to its own trap before going into the condensate pump or boiler feed tank. The zone then runs its own pressure and the boiler can do whatever pressure it wants. Basically you pipe each zone as though it has its own boiler and the zone valve and trap/condensate tank isolates the zone from the common boiler.

@realliveplumber They tapped it off the side beacause it was easier and they didn't know what they were doing anyhow.


The right way to do a zone valve (if you must have one) is if the pipe is pitching down to the valve inlet put a drip on the inlet pipe and drip it back into the boiler or into a wet return to keep the condensate off the valve when it is shut. Not into the boiler supply or header.

If faced with the opposite....zone valve installed in a pipe pitching up the inlet side will be fine if the condensate can drain back counterflow. On the outlet side it will collect condensate when the valve is closed drip it through a check valve installed below the boiler water line or use a steam trap and drip either one to a wet return.

Steamhead said:

Steamhead said:

ISTR that shows up in Lost Art someplace, but I don't have mine handy- @DanHolohan ?

Well, I stand corrected- as far as I can tell, this isn't in Lost Art. But I know I've read it somewhere.........

https://heatinghelp.com/systems-help-center/zoning-steam-systems/
The last sentence

I may be wrong, but I'm almost certain I've seen large flanged (four, five or six inch) steam zone valves with that bypass built in. Possibly Minneapolis Honeywell?

I have never seen a set-up like that with copper lines that bypass the zone valves. They may be doing this as a bypass to overcome holding condensate in the piping. I may put just enough steam in the piping to break the vacuum but not enough to add heat to that zone. On a 2 pipe system you need to make sure that you have the system vented properly with or without vacuum breakers on the return lines. On a 1 pipe system the vents on the radiators solve the problem. Normally, on a steam system that is zoned, each zone should have a drip trap installed before the valve to get rid of any condensate that may be present before the valve. On this job however, the zone valve may be close enough to the header and the boiler that the drip trap may not be needed although if I were installing the zone valves I would have done the job correctly and installed the drips. As to the necessity of a condensate pump system, every job is different. Some jobs need them and some do not. As @ScottSecor mentioned, I knew of 2 ways on large steam systems to install zone valve, they were either installed with a "step control" to open the valve very slowly in steps or a 2nd small bypass valve was installed that would open first to warm-up the zone before the large valve was opened. As I have said many times in my 40 years in the business, every day you can learn something new and today was no different.