Vaporizing 1 pipe steam?

SteamCoffee

I’ve seen old ads talking about this, basically vent replacements. Or full blown Mills/Paul system. Anyone have any experience or numbers about how to do it? Will a standard shut off valve, when fully opened of course, allow for a naturally induce vacuum to occur? Thanks!

ethicalpaul

No, the standard ones really won't, not for very long. The vacuum appears, no problem there, like clockwork at the end of every call for heat when the steam collapses, but it doesn't stick around very long.

There was a Hoffman "vacuum vent" model out there, I can never remember, it's 75 or 76, that would apparently hold a vacuum better. It's out of production.

I tried to make a vent that would hold vacuum but the difficulty I had was how to let it vent at very low pressure (like a few inches of water column), and also make it hold fast against vacuum.

I let it go as a thing I worry about because my (and others') one-pipe systems already work really really well without it.

bburd

Vacuum was a useful idea in the days of hand fired coal boilers. The system would continue steaming at reduced temperature as the fire died down without attention and the vacuum formed.

Vacuum was applied to some automatically fired larger two pipe systems as a way to speed distribution and control steam temperature in milder weather. The main problem was the need for frequent maintenance to keep the system tight (free of air leaks at valve stems, etc.) and the steam traps working. Vacuum pumps don't last long if the condensate gets too hot. There is good reason why vacuum systems are no longer installed.

SteamCoffee

The best part of vapor 1 pipe would be to smoother on/off peaks and valleys. Gas boilers have enough stored energy to keep steaming at reduced pressure for quite a while. The “coal only” is something that comes up around here from time to time. But it was highly touted by Dunham and others, even for 2 pipe gas and oil boilers. I would guess that they thought it was good enough to spend money marketing it. A kind of Poor Man’s 2 pipe Vapor. The Paul system seemed to be more about distribution than vacuum/vapor. I guess Packless 1 pipe supply valves must have been suggested in their conversion plans

mattmia2

2 pipe vacuum pump vacuum systems run in to problems when they have bad steam traps and steam makes it back to the vacuum pump or they have so many leaks the vacuum pump can't maintain a vacuum.

SteamCoffee

Very true! They don’t age gracefully. My 1 pipe solution would hopefully be less troublesome as the traps and returns wouldn’t be another headache source. Gotta track down some of my literature

Jamie Hall

Please keep in mind that there is a world of difference between vapour systems, which may or may not operate in a vacuum, and vacuum assisted systems.

The key to vapour systems is in very small, tightly controlled pressure differentials between the steam main supplies and the dry return lines. These differentials are usually on the order of 4 to 6 ounces per square inch differential pressure. The absolute pressure at which they run has nothing to do with the characterisation. The absolute pressure in the system at any given time does affect at what temperature the vapour will be produced, of course. This is where the "dying coal fire" notion comes in -- as the fire died, the system absolute pressure dropped below atmospheric and, correspondingly, the temperature at which the water boiler also dropped (so did the temperature at the radiators at which it condensed) and so it was possible to make use of the lower temperature heat output of a low or dying coal fire.

The tightly controlled differential pressure makes it possible to control, equally tightly, the relative heat output of the various radiators using calibrated valves or orifices, and sometimes makes it possible to do away with steam traps. Not always, however, as steam traps were and are common on vapour systems to prevent any possibility of steam getting into the dry returns -- which would upset the pressure differential.

The vacuum vents which were used, of which the Hoffman 76 is an example (it is still produced, by the way, if you have the cash to pay for it), allowed this drop in absolute pressure while not admitting air to the system.

Many of them had -- and have -- various ingenious devices to ensure that the pressure differential stays low -- the dreaded Hoffman Differential Loop is one -- to ensure that the condensate could, in fact, return to the boiler without difficulty.

Vacuum assisted systems are a different critter altogether, and are much more akin to one pipe systems. In general, the vacuum assist was used to evacuate air more rapidly -- potentially at a lower absolute pressure in the boiler, but not necessarily -- from the system.

Vacuum assisted systems are not particularly fussy about vacuum leaks -- the vacuum pump can handle the leakage, or should be able to. Depending on the vacuum pump type, however, they can be very unhappy if they get steam in the lines to the vacuum pump. Vapour systems don't care about vacuum leanks, unless they are intended to drop below atmospheric pressure on cooling, in which case they certainly do care, and maintaining a large system to be really vacuum tight is an ongoing battle.

A couple of other considerations. First, there really isn't enough residual heat in even a large cast iron boiler to make much difference unless one is going for that last tenth of a percent of efficiency. Second, controlling the absolute pressure at which the boiler operates requires sensitive devices, such as a vaourstat, maintained and mounted so that it can function properly. If one wanted to run a vapour system at sub-atmospheric pressures (i.e. a "vacuum") -- which has some interesting theoretical advantages -- the control mechanism has to be sensitive to the pressure differential between the mains and the dry returns. This can, of course, be done, and was in the days of coal by differential sensing damper controls (the efficiency on part fire was horrible, by the way) -- but it is not how modern controls work. It would be advantageous if one could design a modulating oil or gas fired burner which
was differential pressure sensitive. I haven't seen one.

Bottom line: don't confuse vapour steam systems with vacuum assisted steam systems. Not the same animal at all.

PMJ

SteamCoffee said:

The best part of vapor 1 pipe would be to smoother on/off peaks and valleys. Gas boilers have enough stored energy to keep steaming at reduced pressure for quite a while. The “coal only” is something that comes up around here from time to time. But it was highly touted by Dunham and others, even for 2 pipe gas and oil boilers. I would guess that they thought it was good enough to spend money marketing it. A kind of Poor Man’s 2 pipe Vapor. The Paul system seemed to be more about distribution than vacuum/vapor. I guess Packless 1 pipe supply valves must have been suggested in their conversion plans

I'll say, and in my opinion understated. It is something that really needs to be experienced first hand to appreciate fully.

The dead men went to great lengths to keep air out. That wasn't because they were stupid.

SteamCoffee

I’m very well versed in the rather dizzying array of these critters, I have a small collection of Air Eliminators etc. just waiting for the right time to put them to work.😋. They are fascinating for sure. I’m referring mainly to 1 pipe conversions which were advertised as, and I’m sure we’re, great improvements. A way to cater to folks already in possession of 1 pipe. Firing under vacuum is the fastest way to get steam where it’s needed. A nice Benny, but 1 pipers suffer from the “flamethrower effect” all on or all off. Smoothing those peaks and valleys out would seem like low hanging fruit for optimization purposes. Yes, this would be best for hand fired coal, but that was for a relatively short period of time (my grandparents bituminous boiler was my job on vacation,) and stoker inserts just about made them vanish. We’ll see about residual heat helping, I’m up for trying it.

CLamb

ethicalpaul said:

There was a Hoffman "vacuum vent" model out there, I can never remember, it's 75 or 76, that would apparently hold a vacuum better. It's out of production.

There is a 76 in a recent Hoffman catalog but it is a main vent. I wonder what it looks like on the inside.

mattmia2

The easier way to smooth out 1 pipe would be to cut the boiler off when the radiators are only partially full of steam then fire it again and repeat as needed, lengthening the cycles as it gets colder out.

Jamie Hall

I'm always vaguely intrigued by how much people are opposed to turning burners on and off. I'll grant the need for a prepurge and post purge for any larger burner. However, beyond that, why not fire right back up again before the boiler has a chance to cool? Granted, if the thing is badly oversized that won't work well -- but if it's less than 50% over... but maybe I'm biased by working with old engines, almost all of which were governed by simply turning the ignition off when the speed got a bit high, and turning them back on when it got a bit low. Even some aircraft engines as late as the early twenties were controlled that way. And, of course, all diesels are controlled by varying the length of the combustion event (and some of the largest by shutting off the fuel completely at close intervals when developing low power or idling). It helps to have a good flywheel... but a boiler is a pretty good flywheel, in the thermodynamic sense.

PMJ

mattmia2 said:

The easier way to smooth out 1 pipe would be to cut the boiler off when the radiators are only partially full of steam then fire it again and repeat as needed, lengthening the cycles as it gets colder out.

That should be done as the first step anyway for sure. I've done a controlled partial fill off and on by remote temperature sensor for many years. Evenly spaced firings always then with the frequency and length controlled by the demand.

SteamCoffee

I’ve seen much on 2 pipe vapor, vacuum assist etc. obviously a major improvement. It seems that, for instance, the much greater heat retained in 1 pipe mains may be of benefit. The ASHRAE stuff I’ve read implies the improvement of cooler return mains as proof that the heat was given up where you want it, the rads. 1 pipe, especially counter flow, would seem to store more heat. Heat, that could wait up to a deep vacuum rad? With as many 1 pipers that are still out there, it seems some scholarship to discover (rediscover?) some efficiency gains. Time to hit the books.📕

Jamie Hall

Hitting the books is probably not a bad idea, at least sometimes. The physics of what is going on is really pretty basic, and so is the thermodynamics (which of course is really part of the physics...). Where things start to go sideways a bit is in applying that to the real world, and in the actual engineering -- which is the fine art of applying the physics (or whatever) to real situations to come up with a result which meets, but does not exceed at least by much, the expectation of the party requesting the design. Which often involves a lot more than just the physics (there's a good reason that it used to be -- don't know if it still is -- that 20% of the questions on the PE exam were economics...).

ethicalpaul

Jamie Hall said:

I'm always vaguely intrigued by how much people are opposed to turning burners on and off.

This is what the pressuretrol does, as everyone here already knows, but people freak out and call it "short cycling" and don't want it to happen. I don't get it either.

mattmia2

ethicalpaul said:

Jamie Hall said:

I'm always vaguely intrigued by how much people are opposed to turning burners on and off.

This is what the pressuretrol does, as everyone here already knows, but people freak out and call it "short cycling" and don't want it to happen. I don't get it either.

if you believe the math instead of the inflated ibr numbers then that won't happen...

ethicalpaul

Well sure, you know that, and I know that, but since so many others don't and install oversized boilers, they cycle and life goes on

Waher

Converting traditional 1 pipe and two pipe systems into vacuum systems is @izhadano 's thing.

See his thread here:
https://forum.heatinghelp.com/discussion/178559/new-steam-heating-retrofit-method

PMJ

@Jamie Hall ,

I'm not sure what you mean by this:

"The key to vapour systems is in very small, tightly controlled pressure differentials between the steam main supplies and the dry return lines. These differentials are usually on the order of 4 to 6 ounces per square inch differential pressure. The absolute pressure at which they run has nothing to do with the characterisation. The absolute pressure in the system at any given time does affect at what temperature the vapour will be produced, of course. This is where the "dying coal fire" notion comes in -- as the fire died, the system absolute pressure dropped below atmospheric and, correspondingly, the temperature at which the water boiler also dropped (so did the temperature at the radiators at which it condensed) and so it was possible to make use of the lower temperature heat output of a low or dying coal fire.

The tightly controlled differential pressure makes it possible to control, equally tightly, the relative heat output of the various radiators using calibrated valves or orifices, and sometimes makes it possible to do away with steam traps. Not always, however, as steam traps were and are common on vapour systems to prevent any possibility of steam getting into the dry returns -- which would upset the pressure differential."

I continuously monitor the pressure difference between my boiler header and the dry return, and I see a difference of 1" of water maybe 2" at the end of burns when the system is above atmospheric. I have seen no evidence of any need to control anything let alone tightly. The whole system is at the same pressure wherever that is above or below atmospheric (lowest like -6" Hg) and the radiators always stay ever so very slightly lower than the mains(because steam is condensing fastest there) so the steam never stops flowing.

I have found the whole thing to be a total no-brainer....just don't let the air back in and then it takes care of itself.

SteamCoffee

Sub-atmospheric was all the rage before the Depression then ww2 put an end to craftsmanship. In a perfect world I’d install Dunham Differential System in. With basic computing power, matching the temp outside with the desired inside temp would be great. Using 100% of your radiations capabilities would happen very infrequently. The ability to make down to 150F steam? What’s not to like. Now, if some manufacturers would spend some money on a practical modulating boiler to match….on can dream..

PMJ

SteamCoffee said:

Sub-atmospheric was all the rage before the Depression then ww2 put an end to craftsmanship. In a perfect world I’d install Dunham Differential System in. With basic computing power, matching the temp outside with the desired inside temp would be great. Using 100% of your radiations capabilities would happen very infrequently. The ability to make down to 150F steam? What’s not to like. Now, if some manufacturers would spend some money on a practical modulating boiler to match….on can dream..

Having used it for many years now I do understand why this was.

Please consider the simplicity and low cost of a custom PWM control. It takes shocking few additional evenly spaced burns to achieve most of what you are looking for. Coupled with sub-atmospheric between burns it is a different world of comfort altogether. This I know from having lived in both worlds.

SteamCoffee

It’s a shame to see then end of this system for residential use, but the post WW2 demand for housing ment speed over alles. My house shopping last week had ONE boiler out of 9 piped correctly. I may splurge for Paul vents and run my own pump.