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My feeling is that the Dimension A probably is more applicable to larger systems than typical residential stuff.

There are a lot of old building using 1 pipe steam that are a lot bigger than a typical house. Bigger systems usually +more pressure drop.

@RayWohlfarth

Not just steel but CI as well. A lot of the old CI boilers were 1pipe out (supply) and I Pipe in (return with a swing check)

Commercial stuff usually has (or is more likely to have) a condensate return tank or boiler feed tank so it doesn't need a Hartford Loop.

Equalizers have to be on a CI boiler now because they throw water into the header. (would be much better if the water stayed in the boiler like it did with old boilers) Steel boilers like a Scotch or Steel fire box boiler have a large area inside to release the steam from the water. On a CI boiler that space is all cut up into individual sections ....by the sections. Every section is an individual boiler. Steel boiler are just a huge tank of water with fire tubes running through them. No restriction on water or steam flow. CI The water and steam have to navigate all these passageways in the sections and the sections will run at different temperatures. A CI boiler with a power burner will always get hot and steam the rear sections before the front.

That's why on CI we need all these equalizers and external headers that a steel boiler can survive without.

And yes. The Hartford Loop was originally supposed to keep water in the boiler if the return line leaked but the best it could do is buy them some time. Coal fired there was no low water control. A lot of the old coal CI boilers had a fusible plug above the combustion chamber. If the boiler finally got low on water the plug would melt when the water got low then it would dump the remaining water on the coal fire in hopes of putting it out.

jmho

Even a huge steel boiler only has 1 supply weather it is 8, 10, 12" whatever no boiler header, no equalizer

We should always have these discussions. When someone actually measures the actual performance of an assumption made by some dead man that maybe had a unique situation and therefore applied that "RULE" to every system regardless of the differences in the systems, we can see the "Myth Buster" at work. Thanks Paul for your comments and video. You actually taught me something so many months ago after our extensive discussion on that subject.


The fact that the "Dimension A" is part of Steam textbooks means that at some point there was an issue, Could it have been on a system with steam mains that were too small and therefore there was a significant pressure drop off, or were there other factors …only the dead men know. But the explanation Ray offers does have its basis in physics of water and pressures and the like. So understanding that IF you happen to come across a one pipe system that does have that pressure drop issue, the Dimension A will resolve it. IF (and that is BIg IF PAUL) you find it, you can see the fix in your mind's eye without the need to install glass pipes and pressure gauges all over the place. But I really like the Weil McLain glass boiler and @ethicalpaul's glass pipes.