\"Open Return\" Vapor Heating from England (Steamhead)

Steamhead

It's what we would call "Orifice Vapor" here in the States. Note the "syphon" (water seal) connecting the ends of the steam main and dry return- I've actually seen a similar system about fifteen blocks from my house in Baltimore, but there were no names on it.

Also note the "safety tank" which was used to keep water from reaching the open vent pipe.

The optional Heintz traps mentioned at the bottom used semicircular Bourdon tubes instead of the usual bellows units, like the old Haines traps did.

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Christian Egli

Things on my mind, thanks for the work out

Dear Steamhead,

I saw your post earlier, and suddenly my evening got booked solid. The overflow safety tank has given me much to think about.

I got suspicious when I read that this system needs a very even boiler pressure, more importantly, I think it needs a boiler pressure that never exceeds a very low maximum, probably 1 or 2 PSI depending on how high the basement ceiling is.

It seems they were worried about any excessive pressure since they piped the overflow from the safety tank into the ash pit, presumably to douse the fire. What a mess this must cause, first the water mixes with the ashes, then the blast of steam... It's good thinking to make the ashes wet first, otherwise you're likely to get a great puff of dust. What's better, dusting or mopping?

The way I understand it, as the pressure rises in the boiler, the water will back into the return lines, up what looks like the usual A dimension. But here, it is not just mainly pipe loss the water column has to keep up with, it's all of the boiler pressure, since the return main is always open to the atmosphere. In fact, the return might even be under vacuum since it is piped into the ash pit, that makes for an even bigger pressure difference. Everything will be fine if the basement is deep enough so that you can squeeze about 2 1/3 ft of altitude between the water level and the return for each PSI of pressure difference. This altitude determines the maximum operating pressure.

It seems the logic behind the tank is to provide more space for the rising column of water to go to. As the pressure goes up, the water in the pipe goes up. It could keep going, way beyond the height of the ceiling, but since that is not practical, in this scenario, the column of water has been provided with a whole tank to fill leisurely instead of having to climb up an endless pipe. But, here is why I think the idea of a catch-all overflow tank makes for bad physics. Pressure in fluids is solely a function of height, not the shape of the vessel and not the volume. Pascal figured all of this out at the time of Louis the Fourteenth, the Sun King. They had radiant heat then already, but not steam heat, the best things were still to come.

In this hook-up, if you have a raging fire, evidently your boiler pressure is likely to go up. At that point you'll slow the combustion by closing the damper on the ash pit and now, all the draught caused by the fire and the chimney is sucking on the overflow-tank-to-ash-pit connector, it's the only breather left. All this makes the water back out of the boiler, and the level will quickly rise in the return pipe and if that's not enough height, the level will rise just as quickly in the overflow tank. Even though the volume of the tank is large, it will not in any way slow the rise of the water column, that's just physics, but it will seriously mess with the boiler water level. That's when phase 2 kicks in as the boiler water line passes below the intake of what they called the safety pipe. Now, your system will "safely" flush the steam into the ash pit. Sounds to me like a CTRL-ALT-DELETE action.

Oh, but the return main was not flooded. What a victory! You only flooded your basement floor like Mount Saint Helen erupted there, that's cool.

When was the Hoffman Differential Loop invented? It would have done everything they had wanted in this scheme and some more. This idea just looks like an open vase expansion tank recycled from a hot water system, the ones that used to be installed in the attics. But with steam , I don't see how the tank will buy you any time or safety. All you need is height, and love... with these old things.

The system you have seen near you, is it similar only in the way of the syphon or also the safety tank? Does it show evidence of having had some boil-overs? Nasty ones? What pressure does it run at?

Hey, thanks for digging up this old stuff. You can see how I made good use of my evening. Does whatever I wrote make any sense or have I got a case of Saturday night fever?

See you in the morning. Best regards.

Christian Egli

Steamhead

Back then

it wasn't easy to keep boiler pressure so tightly controlled. So the Safety Tank, Differential Loop (1926 I believe), Return Trap and other goodies were invented. Nowadays we use the Vaporstat that cannot be set higher than 1 pound, so none of the above are needed.

In this system, the Safety Tank was installed ABOVE the level the water would rise to under normal operating pressure. It only received water if the pressure got too high. Yes, it would overflow eventually, but it bought you some time.

The ash pit of a coal-fired boiler was normally not under a negative draft. The resistance was in the coal bed itself, above the ash pit. A negative draft existed above the coal bed, and many Vapor manufacturers like Broomell, VECO, Mouat etc. took advantage of this. However, if steam was released into the ashpit it would probably rise into the coal bed, slowing or extinguishing the fire.

The Safety Pipe appears to be a variation of the setup Stephen Gold used on his first boiler (see Chapter 1 of Lost Art). That one had a sight glass with an open top. If the waterline dropped below the sight glass inlet, steam would escape.

The system near my house has the syphons as illustrated above. I've never seen them anywhere else. If it had a Safety Tank, it was removed when the boiler was replaced by a local butcher.

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Christian Egli

You can't stop progress

Thanks for the added info.

I have never seen a syphon either, neither old nor new like the one Dan Holohan describes for adding baseboard fin tube radiation to a one pipe steam system.

I'll keep looking though.

Best regards

Steamhead

I've used them

to isolate wet-return drips where they connected together above the boiler waterline, and lowering the entire wet return to a point below the waterline was difficult or impossible.

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