Steam - condensate connection in a 2 pipe system

shakingthrough

Hello everyone,
I am a relatively new owner of a 3 story house built in 1930, and have been fascinated to learn about its steam heat. I have now read two of Dan's books and watched some of the online videos. As a physician I have particularly liked the analogy of a steam heating system being compared to a living breathing organism. I like to think of the steam going to the radiators as oxygenated blood going through arteries to the organs, and the condensate like the oxygen depleted blood going back to the heart through veins.

And therein lies my question. Within a few feet of my boiler and its near-boiler piping, I have three wet returns that all eventually join right next to the boiler, with two main air vents. But a few feet upstream each of these returns has a vertical run that connects with the outgoing steam. As you can hopefully see from the two photos that I attached of one example, they connect not only on the bottom but also on the top which also has a trap. The insulated steam pipes course along the basement ceiling to supply several basement ceiling radiators and then also supply steam to my first floor and I believe the upper floors as well. By the way it is a 2 pipe system. Each radiator or convector has an individual supply and then a trap on the outflow before the condensate enters a separate return pipe.

In medicine we call an abnormal connection between an artery and a vein a fistula. Why does my system have these 3 "fistulas"? I haven't been able to find anything in a book or online that refers to similar. I have no reason to suspect this is not original piping. And I presume the Dead Men who built my system knew what they were doing, as in general everything heats fine. But can anyone explain the why to me?

Thanks very much,
Bill

Pumpguy

I'm not an expert in these matters, but the 2nd picture with the line coming off the top of a steam line through a thermostatic trap and dropping into a return line looks like an equalizer line to me.

If it is an equalizer line, the cooling leg is too short and should have a minimum 6 foot length. This is to allow some condensation to take place.

The attached file goes into detail.

I have no idea what the 1st picture is all about.

I am sure others will be able to offer more information.

mattmia2

On 2 pipe steam, the air from both the mains and the radiators vents through the returns. The crossover trap at the top of your main vents the air out of the main in to the return where it then vents from the dry return out of a vent. The connection from the mans below the water line allows the condensate that forms in the mains to run in to the return but because it is below the water line, steam from the main can not get in to the return.

shakingthrough

Thank you both very much. It all makes more sense now - basically they are functioning like equalizers I presume, one for each return. There is also an equalizer coming off the boiler, but for some reason they must have felt these were necessary as well.

So now I have a follow up question - reading that it is smart to insulate the condensate returns as well as the steam lines, is there ever a reason not to insulate them? None of my returns in the basement are insulated (as evidenced by my photos above). I was going to try to tackle the addition of fiberglass insulation on them.
Bill

Pumpguy

2 pipe vacuum return systems like cold condensate. The colder the condensate, the more efficient the vacuum pump becomes.

When asked what's a good temperature for a low vacuum (average 5.5" Hg.) system, I advise 145*F.

For a deeper vacuum, its best to have lower temperature.

See the attached file.

I have been told customers want hot condensate coming back so they don't have to add more heat to bring the water up to boiling. But this argument doesn't take into account the amount of heat for change of state, which is a very large percentage of the total heat input.

I am now seeing boiler feed units with steam tubes to elevate the feedwater temperature before its sent to the boiler.

mattmia2

This isn't a vacuum(at least not pumped) system or even a pumped return system, it is just a plain 2 pipe gravity return system. The steam trap is necessary to let the air out of the steam mains and the pipes that drop to the wet returns remove the condensate that forms in the mains. There are other ways to do it, for example the crossover trap is fed from the bottom of the main and it passes condensate and air in to a dry return. Another option is there are vents in the steam mains to vent the air and there are drips for the condensate in to a wet return to pass condensate but not steam.

Steamhead

@shakingthrough , that piping pattern looks familiar. Are there any devices in the piping near the boiler, such as a Differential Loop or Return Trap? post pics if you can.

shakingthrough

I am unfortunately away for work for a few days. And I didn't previously know what a Differential Loop was until I just looked it up. But I think I actually may have one right next to my boiler. I had previously tried to take a photo of a few of the parts I could not identify, and have attached a horrible photo of a rusted name plate on it. It is hard to access because it is somewhat obscured by ductwork for a since decommissioned system for humidification. Looks the same as a few images I found online that say The Hoffman Differential Loop, The Watchman of the Waterline. So cool. I will try to send a few better photos when I return home later in the week.
Bill

Steamhead

That's what I thought. I'll wait to see your pics.

shakingthrough

Sorry for the delay but I finally had time to take a few more photos. And in the meantime I live in the Chicago area and just connected with the Steam Whisperer today - Dave is now coming to my house in a few weeks to look everything over. I know he is active on this forum, but to close the loop for everyone else (no pun intended) here are photos of my 25 year old Weil-McLain boiler with a Mercoid Control device. Another image looks up at the two large Gorton (I presume) vents that are in place just above my differential loop. What puzzles me is that someone cut into the plaster ceiling to fit them in, which makes me wonder if they are truly in their original position or not. They are obviously difficult to access, and I plan to open up more of the ceiling before Dave's visit. Then there is a photo of the Hartford Loop, the lower half of the differential loop (whoever painted the boiler room before we bought the house must have been paid by the gallon), and then one of two smaller Gortons I have on the returns. I told Dave on the phone that they sometimes spit out some water in addition to air, so that is one of the things he will be troubleshooting. I will report back on his findings/recommendations after his visit. Thanks again to all - I am truly enjoying learning about all of this.
Bill

Jamie Hall

That second picture is of a crossover trap. It connects the steam main -- on the right in the picture -- with the matching dry return -- on the left in the picture -- and serves as the main vent for that particularl steam main. The dry return takes the air that goes though the trap and returns it to the boiler, where the main vents for your system (the two Gortons in the second to last picture) release the air to the atmosphere. That's all the venting that your system needs -- or should ever have.

Not an equalizer.

The vertical lines drop down to a wet return and serve to take condensate which gets into the dry return to the wet return and then back to the boiler. They may also come down from the steam mains, depending on which way the pipes are pitched. There are two such in the picture of the crossover trap, one for the steam main and one for the dry return at that location.

All the dry returns should come together at the boiler ABOVE the water line and be vented by the main vents. All that should happen very close to the top inlet (return) on the Loop.

You need to remove ALL the other vents, whether on the mains or on the dry returns. They don't belong there, they aren't needed, and they will cause trouble.

You mention two other smaller vents which are on the returns. Besides getting rid of them, they may be telling you when they spit that your boiler pressure is too high. One of the things the Differential Loop does is it ensures that the differential pressure (hence the name) between the steam mains and the dry returns never goes too high -- specifically, around 8 ounces per square inch. It does this by admitting some live steam into the dry returns -- and those more distant vents may not close properly when that happens (the big Gortons near the loop will, almost instantly, as they should).

The mercoid is a nice control device, though I'm wondering it if is functioning in this set up. However, it is not sensitive enough for a Hoffman equipped vapor system. You need a 0 to 16 ounce Vapourstat, set to cut out at 6 OUNCES and cut back in at 3.

shakingthrough

Jamie thank you very much. I understand it significantly better now, and look forward to making the necessary changes to improve our system. I will post updates as I have them. Regards -
Bill