Single Pipe Vacuum

mcsteamy

I've been thinking (which is always dangerous) about ways to improve the efficiency of my heating system without putting too much time or expense into it, and the thought I can't get out of my head is this:  Vacuum on single pipe steam without Paul air line vents still makes perfect sense.  The fact that we don't have coal should not matter for a hill of beans, really.  That has already been show with two pipe systems (which bucked the then-conventional inherited wisdom).  Why not with single pipe?



Years ago, of course, Hoffman and other produced just such a thing with the Hoffman vacuum vent.  As time went on, the vents didn't sell, and eventually you couldn't buy one no matter how badly you wanted other than the odd lot or two that would show up on eBay. 



First things first:  None of this makes any sense at all unless it actually lowers heat bills, and the only way that happens in a decently insulated house is if more heat from the fuel goes into the heated space instead of up the chimney, distribution and room temperature issues notwithstanding.  So, from a purely theoretical perspective, is there potential here?  I have to think there is.  When I want to make steam, my boiler fires, and heat goes up the chimney while heat does not go out into the room.  When the water gets to temp, heat goes into the rooms.  When the boiler shuts down, heat ceases.  Meanwhile, on my natural draft boiler, 100+ pounds of water slowly cools down and (for the most part) dumps the heat through the draft hood up the chimney.  If any does make it into the basement, odds are most of goes out the old stone walls. 



Let's assume the boiler holds about 130 pounds of water, and that my achieving a vacuum allows the water to boil at, say, 20 degrees lower temperature.  So on a call for heat, we have heat from 20 degrees of temperature rise we otherwise would not, and 20 degrees of temperature fall we otherwise would not.  My rough math says that's about 2600 BTU each direction, or 5200 BTU per firing cycle in heat that goes into room instead of up the boiler's draft hood.  One CCF of natural gas contains 100,000 BTU, give or take.  Assuming my boiler operates at 80% efficiency, and I have 40 firing cycles in a day during the heating season, that's 260,000 BTU or about 2.5CCF of gas being wasted per day.  Assuming that a CCF costs around a buck, that's $2.50 a day, $75 a month during the heating season. 



I'm making a lot of assumptions, and the losses and gains assumed are probably optimistic, but is there any reason to believe this isn't at least partially accurate?  All of the old literature suggests that there were real savings to be had, and by my estimation, the source of the BTUs shouldn't make a lot of difference because, through whatever mechanism, the fuel source is being used more efficiently, and it seems most of those gains occur because heat is able to be moved to rooms when otherwise it would not be.  Whether coal or gas, this would still hold true.



Objection #2 to single pipe vacuum is that the system needs to fully remove all of the air when a vacuum is naturally produced.  Perhaps someone can explain why this is a problem, in scientific terms.  If all of the air isn't removed from the system, won't it just equalize in the system and result in a lower, more imperfect vacuum?  All vacuum systems eventually lose vacuum due to leakage of air back in.  It seems to me that radiator which has air left in it would simply have that air distributed through the radiator, and then the piping.  Gases tend to work that way, particularly where pressure differentials are concerned.  Then, when the boiler fires, steam will still move as it ought to--from high pressure at the boiler to the lower pressure in the pipes.  It seems thoroughly implausible that half the radiator will have a vacuum while half the radiator is air locked running into the next firing cycle.  All we'll have is a lower vacuum...  Yet, this is perhaps the #1 objection raised to the old single pipe systems firing on gas.  I submit that it is nonsense.  A few old, anecdotal stories on this board of properly operating single pipe "relic" vacuum systems seem to provide at least some empirical backing for this, too.



Problem #3 is finding vacuum vents.  However, couldn't something like this: <a href="http://www.usplastic.com/catalog/item.aspx?itemid=85435%C2%A0">http://www.usplastic.com/catalog/item.aspx?itemid=85435 </a> installed on each radiator in front of the vent do the trick, along with a thermostatic trap with a swing check on the main vents?  I found another manufacturer that advertises a 0 psi cracking pressure, which would be even better, but I haven't called about pricing. 



Assuming none of this is completely off the reservation (which it may well be) it seems that for under a hundred bucks in cheap little valves I could be saving a lot of fuel....



This is a just a "toss it out there" idea at this point that I haven't spent the time to fully develop, but I thought it would be interesting to see if there are any real critical flaws to single pipe vacuum that have been tried, tested, and proved other than being just second-hand wisdom... The benefits seem enticing.



(It seems some of this was covered a few years ago, and Igor Zhadanovsky did a little bit of field work (and filed some rather ungainly patent application with about 13 different ideas all rolled into one, many of which were little more than a recitation of 90 year old prior art (see:  Hoffman #2) which he may or may not have been aware of or credited--I don't recall).  It sounded like he also conjured up a system using 1psig check valves, but the investigation basically died out after that.  Hopefully we can reignite the fire, a bit.)

Mark N

Air

I think the problem is the air that doesn't get vented expands to fill the vacuum and the air checks are closed because the system is under vacuum. When the boiler fires back up the air can't vent out because the vents are closed and because the air can't get out the steam doesn't move.

MDNLansing

Here's What I Can Add

A common misconception people have is that vacuum systems only worked with coal. It's just not true. I have an Eddy Vacuum system that was originally installed around 1907 with a gas boiler.p My house never had a coal boiler. Vaporvacuum's place is the same way. These systems do in fact work quite well with gas boilers.



However, the original gas boilers ran 24 x 7. There were no thermostats, they modulated the burn with the gas valves. I suppose they didn't know much and catalytic process and certainly were not concerned with CO stats in the stack. They would just draw a vacuum, and slow the burn low a coal boiler. Like you mention, these systems took advantage of the lower boiling point of water in vacuum. Instead of 210 degree steam, you could hold the radiators at 160 degrees which was great at the beginning and end of the season. Great idea.



Even though these systems are typically 2 pipe, the second pipe was only for air. At the time, manufacturers had to invent the vacuum vents and it as far easier to centrally locate one of them instead of needing one on each radiator. The addition of the air lines was just to vent the air to a single vent. This aside, they are essentially single pipe systems, so there's no reason a single pipe won't work.



All of that said, now you need to decide it it's worth it. There are a few things I have been investigating. First off, the lower temp boil. This does have some technical benefit in today's modern systems, but not very much. If you draw 20"'s on the system and let it sit, the radiators will stay hot and hold heat for quite some time. The advantage with vacuum here is that with the proper seal, you are retaining the steam and heat and not diluting it with air, and thereby condensing it. But the lower boiling point isn't an issue. On a modern boiler, the heat cycle will run until the thermostat is satisfied, or the high pressure limit is hit. So 20" of vacuum just puts you 20" further back from the pressuretrols goal of 1.5 psi. The low boil only comes into play of you are going to modulate the burn and boil for a long period of time at 170 degrees. Otherwise, you're boiler will overcome the vacuum on it's way to the cut out pressure and take away that advantage.



The second challenge is, as you pointed out, venting. Without the second pipe, you can in fact vent the radiators will multiple products, traps and such. The issue I have run into looking at atmospheric venting with vacuum systems is with I call check valve chatter. Once the system steams up and shuts down, the pressure in the radiators continues to rise slowly for a few mins. When this happens, a swing check on the radiator will chatter. They do have 0 psi crack points, but they also fall back down and bounce back up and fall back down and so on. This will make the all chatter like crazy for for a few mins after shutdown. Make sure you test this thoroughly. I was unable to overcome this issue, but that doesn't mean it's not possible.



Third, the biggest benefit. As deep cold has set in here in my region, I am now seeing the biggest benefit of vacuum with modern boilers. Once the vacuum is drawn, most of the air is out of the system. If you can hold that vacuum until the next cycle, that's that much less air you need to vent. This has an advantage and disadvantage. When it's really cold out, the boiler will cycle often. So lets say you have 15" of vacuum left for this cycle. Boiler kicks in, vents just a little air, then seals up. Once the seals are tight, the boiler drives on to the cut out. Because the boiler isn't working hard to expel the air, this tends to shorten the cycles and ends up making them too short to heat effectively. With each system there is a minimum amount of time the boiler needs to run to generate enough 210 degree steam to rill the pipes and radiators. Shutting down early many have only produced enough steam to 3/4 fill the system. I have been able to use a combination of vents and check valves that "leak" a little air back in slowly to help extend the run times. It took a lot of time and effort, but it can be done. My system vents the mains to the atmosphere, then once they close, then vent to the air returns. My central vent has a Hoffman 76 on the air return line. My system won't seal up and build pressure until this vent gets hot and closes. So, I have to send steam down the air returns to heat the vent ans close it. This wouldn't apply to you, but just remember if you do use a Hoffman Vacuum Vent make sure you devise a way to shut it down while steaming.



Summary

Pros: Less air in system to vent between close cycles, low temp boil if you modulate the burner, solid seal in vacuum uses up all available steam in the system

Cons: Quietly vacuum venting the radiators, Developing custom venting for the mains to create a vacuum seal (traps are the way to go).



Good luck with this.I know you can amp up these old systems. Retrofitting one to an existing single pipe might be a challenge, but with the right amount of trial and error you can certainly do it.



Coming up for oxygen now....

steamedchicago

how does steam move?

You need a pressure differential to move steam, and you won't have one. 



What probably could be made to work is some variation of the Paul system.  No need to run all the lines back to the boiler, you can have electric pumps that do the extraction, placed where it's convenient.  Maybe run some lines to attic, and vent there, some to the basement.  You'd want the outlet somewhere the noise wouldn't matter.   Switch the pumps on when the t-stat calls for heat, turn it off when the pressure hits your low point (and cycle it to maintain vacuum the whole cycle?)



You might be able to get enough vaccum to get earlier steaming, and you'd get faster distribution. TRVs would probably be a good idea.



Seams pretty complicated.  Maybe a vacuum mini-tube system would be less work...

Mike Kusiak_2

Prssure differential

With a vacuum in the system you will certainly have a pressure differential as soon as the boiler begins to generate steam.



 As boiling begins, the point of lowest pressure will be the radiators, and the steam will travel to them to try and equalize pressure. As the steam condenses, It will maintain the lowered pressure until the radiators gradually reach the atmospheric pressure boiling point. Then with positive pressure in the system, any air will vent until the vents close and pressure will rise until the cutout pressure is reached or the thermostat is satisfied.



So at all times during the heating cycle there is a pressure differential. It just may begin at below atmospheric pressure, but the absolute pressure is always positive and highest at the boiler when it is producing steam.

mcsteamy

A few more thoughts

Regarding exhausting air:  A first glance, it might seem like if all the air wasn't exhausted on the first cycle, it would create problems.  After all, we vent to remove air, right?  But this is only partially true.  Any steam system--vacuum or not--starts filling with air every time it shuts off.  If we don't push the air out in the first place, or it leaks back in, what's the difference?  Eventually, any naturally created "vacuum" system hits positive pressure, which will again force air back out, just like it would if there were no vacuum...



So why do we let air back in ON PURPOSE!  System balancing?  Nah.  A slightly longer steam cycle is easily rectified by changes to the anticipator, and would likely REDUCE temperature swings in the building.  And once the vacuum is gone--which will probably happen before the rads fill up again--the vents crack open, and regulate the steam flow.  Ta-da!  Dole, and I believe Hoffman, both made adjustable vacuum vents.  They didn't do this because they didn't work.



Regarding reaching positive pressure:  This was common on the old systems too.  I don't think it mitigates advantages.  Back in the coal days, they actually coaled up the boiler to 8 to 10 pounds of pressure--read the testimonials of the Hoffman #2 vent.   A lot of the advantage was gained from being able to make steam earlier when they were firing up to their ridiculous pressures and hold it longer after they fired down.  They pulled more energy out of the coal pile that way.   Likewise, if we make steam earlier once the gas valve starts cranking out gas, we pull more useful energy out of our gas, right?  And if we pull more out of the pot of hot water after the burner goes down, we save money there too.  I submit that these things disappeared because they weren't probably maintained, and got an undeserved bad rap.  Not because they wouldn't work with a gas burner.



Building a Paul system?  Not cheap.  When we talk about single pipe vacuum, that's always where it goes, sadly, and the idea is dropped.  I'm well familiar with Paul systems, having lived with two of them, now.  Nice system, but the systemic energy savings are questionable.  Using expensive electricity to pull and maintain a vacuum isn't the world's greatest idea with an otherwise modern system. 



I want to explore this to see if there is any reason it cannot be done with $8 valves with a ROI of, likely, a few months.  Valve chatter is a very interesting potential practical problem...



The check valve flutter issue is interesting.  Practicalities of the check valve, I think, are going to be one of the toughest issues.  My thought here is that a swing check in front of thermostatic traps piped to atmosphere ought to work well, and economize on parts on systems with "antler" venting.  Keeping the cracking pressure lower than the radiators would seem to be essential.  Then, the inline spring and ball checks on the rads should work okay.  The listed valve says it isn't rated for steam, but it is good to 250 degrees.  My guess is they're thinking pressurized high temp steam.  not 212 degree boiler steam.  An 1/8" NPT spring check in front of your existing vents would be ridiculously easy, and cheap. 

MDNLansing

And Some More

Remember, the vacuum is drawn to lower the boiling point, then to continue that low fire boil for as long as you can. The only way to do this is to modulate your burner. Drawing the vacuum and then firing up the boiler at high fire will just pressurize the system and move on up to the high limit. At high fire, you're boiler will not maintain the vacuum, it will kill it and bring the system up to positive pressure. It's true they cranked up the pressure on a cycle, but this was only to generate the best vacuum possible. They would crank the boiler up to 8 psi, then damper the firebox and let it fall to vacuum. Once in vacuum, dampers were adjusted to just a slight fire, enough to maintain a little low temp steam. This isn't an easy feat with a modern boiler unless you build your own control to handle this,



As for the venting. There are a few things to consider. Float style vents require well throughout check valve placement. In the wrong place, and too close, the condensate won't be able to drain from the vent reservoir. Make sure you have enough pipe to hold the condensate that flows out of the vent until the check valve opens again. Once it opens, it can flow back out. If the swing is too close the the vent, the reservoir water blocks the swing from opening. Using the bi-metallic vents helps a little because far less water is held in the valve.



As for the chatter good luck! I couldn't over come it.

vaporvac

Two stage-fired boilers?

I would think two boilers stage-fired could take the place of a modulating burner, or at least lo-hi-lo burners.

mcsteamy

Vacuum Conversion

MDN,



You state: "Drawing the vacuum and then firing up the boiler at high fire will just

pressurize the system and move on up to the high limit. At high fire,

you're boiler will not maintain the vacuum, it will kill it and bring

the system up to positive pressure. It's true they cranked up the

pressure on a cycle, but this was only to generate the best vacuum

possible."



I thought that too, but then as I gave this a second glance, I thought, "Well, what are our goals here.  So what if we don't operate in vacuum all the time? Does it actually matter?"



One of the goals of the Paul system was to operate in an induced vacuum so as to lower the radiator temperature--this was touted as a major safety advantage.  Secondarily, lower piping losses occurred because of the lower operating temperature (in the largely uninsulated pipes).  Here, do we care about either of these things?  In the old Hoffman systems, the testimonials seem to indicate that the reason they built a monster fire and then dampered it down was not necessarily to allow operation in a vacuum, but to allow the coal to burn longer without having to shovel.  Granted, this prevented some piping losses, but so long as the coal was burning, unless their stack temps went down, they weren't getting more usage out of the coal.  The only additional heat they pulled out of the coal was the differential between making steam at 180 degrees and 212 degrees, assuming that all of that heat otherwise went up the chimney.  The same holds true here:  Unless our stack temperature goes down, it does not really matter if we operate under a vacuum, so long as we are putting steam out into the system.



My point is this:  Even if we kill the vacuum during the firing cycle, what does it matter?  When under vacuum, we still pull heat from the HOT WATER (which we used our gas to heat) either a) starting at, say, 190 degrees on a fire up, or b) down to 185 degrees on a fire down.  This is the goal.  Everyone always says, "Well, gosh, this was designed for a throttled down coal system so it won't work on gas and you won't get the same benefits."  Perhaps not, but there are still benefits.  Running single pipe under vacuum will not give that long, slow burn.  But we don't need that burn anymore because we don't shovel coal.  But we still boil water.  Will the savings be as dramatic as with coal?  Probably not, since the gas shuts off whereas the coal didn't.  That saves a lot.  But the savings from extracting all of the possible heat from our hundreds of pounds of hot water?  That, to me, should still be available.



Edit:  This raises an interesting point. Would the benefits be as dramatic with a wet-base, forced draft burner boiler?  Assuming the basement is somewhat insulated, this would probably be a pointless project, unless other tangential comfort benefits are available.



There's one guy that did it who posted here some time ago (Igor Zhadanovsky, who I mentioned earlier).  But since he was apparently trying to patent his new "system" (which he apparently didn't realize wasn't new at all), the flow of information dried up.  At least, I'm assuming that's why he seems to have disappeared.   



Here's the patent language (at http://www.google.com/patents/WO2012093310A2):



"By installing a check valve with 1 psi

cracking pressure behind the air vent valves on each

radiator, a hundred years old residential single-pipe

steam system with six radiators was converted into a

vacuum system. Such a simple and inexpensive system upgrade

saved 9 -16% on fuel gas each every month when compared to

the previous years months which had the same average

monthly temperature. In test runs, the 24 inch Hg vacuum was

produced within 80 minutes after the boiler stopped in the

first heating cycle. 22, 19 and 17 inch Hg vacuums were

retained after 165, 260 and 330 minutes, correspondingly.

This timing matches boiler day time cycling frequency in a

cold season but the system ability to hold the vacuum

overnight is not sufficient; a vacuum pump may be employed

to restore the vacuum in the morning."



Talk about low hanging fruit.  The question I cannot answer, though, is why he thinks a vacuum pump is necessary.  Why use electricity to generate a vacuum?  No steam system operates in a perfect vacuum.  All vacuums generated in a steam heating system are imperfect.  All of the air is never out of the system.  Spending money on electric and pumps to mechanically generate a vacuum seems like a poor investment since it will only save you money on a cold start.



Theoretically, I think this works.  You've had some great feedback on some of the practical implementation issues.  I hadn't thought about the water trapping issues in the valve--eek!  My hope is that we can collectively identify appropriate check valves to be used in front of a vent, and other possible issues, identify what ought to work, and take a crack at this.

vaporvac

You solved a mystery for me...

"Back in the coal days, they actually coaled up the boiler to 8 to 10 pounds of pressure..." Thanks for explaining the mystery of the old pressurestat on my coal boiler. I've often wondered why it wasn't a vaporstat as on the gas boiler, although i still need more study to understand how the high pressures worked with a two-pipe vavporvacuum system.

MDNLansing

Doesn't Matter

Pressurizing the system doesn't matter at all, I guess I was unclear on my point with this. What I was trying to point out is that most burners, even on low fire, will be hot enough to generate large volumes of steam, thereby breaking the vacuum and sending the system into positive pressure. There is nothing wrong with that at all. I was just saying that you won't be able to achieve a low temp boil with a standard burner. You will need a way to modulate the burner way, way low. Building up to 1 psi though has no negative effect on performance, it just eliminates the low temp boil state.



The biggest advantage I have seen so far in my lab is venting in the vacuum. Steam distribution is far more even when the system has vacuum and the burner kicks in. There is far less air to vent, and you have created a massive pressure differential in the radiators. If you can acheive 20" in the radiators, and quickly build 1 psi at the boiler, steam flys through the system. With my current boiler and system configuration (it changes weekly) I can vent steam from the ends of my mains within 5 seconds of the burner kicking in when I have vacuum. With the lack of air to vent, the steam can pretty much move as fast as possible. Obviously an advantage.



So far, I think the most promise is in fact with time based cycles. You need a way to "decide" how long and how frequent the cycles should be. Let the system get hold and the cost to the setpoint, and continually boil at a lower temp for a long period of time. Achieve that, and you'll be looking at a highly efficient and very comfortable system.

JStar

Vacuum

What about this idea?



At the end of the main, where the vents would be, you install a 24volt zone valve (constantly powered open on startup), and then a thermostatic trap on its outlet. The zone valve remains open until steam has closed the trap. The valve would be actuated by a simple aquastat attached to the steam main. Once the zone valve closes, it opens its end switch, signaling the boiler to drop into low fire, or shut off 1 of a set of boilers. This will allow you to form a positive air seal, with no chattering check valves, and a direct signal to the boilers that the mains are hot, and high fire can drop to low fire.



It doesn't divorce us from electricity, but it only uses 40 watts.

MDNLansing

Sensitive

Wouldn't this get tricky? Early in the season cycles might be infrequent and the mains might be cool. Deep of winter, the mains might not cool much between frequent cycles. You would obviously want the vent open to start the cycle, even if the main is 190 degrees. Would you be able to cover the entire range of potential temps on the main?

PMJ

Vacuum

I have run my 2 pipe vapor system in vacuum between cycles for years - all natural. I have no vent at all on the steam main, only one on the return. The vent is a 110v solenoid valve in series with a pressure switch set for a plus .1oz or so. The valve opens on fire if there is no vacuum and closes on burner off. The system sinks into vacuum every off cycle. On next fire it takes 1 to 2 minutes to kill the vacuum and the vent valve opens as soon as the pressure switch sees .1oz in the dry return.





The vacuum really speeds up the steam to the rads and evens everything out a lot. Check my other posts on this. Time to steam at the rads from burner on is the whole efficiency game.

Vacuum helps a lot. The only for coal thing - definitely not true.



Oh and one more thing - if you can hear the air coming out of a vent - it is too small.

mcsteamy

Mike,

You said it far more succinctly than I could have!  Your comments are appreciated.  Going through a lot of the old posts that grazed on the topic, your comments were always among the best of them, particularly in terms of dispelling old myths.



It's tough for a lot of people (me included) to think about a "vacuum".  It's particularly confusing here because there really is no such thing as a pure vacuum in a steam system.  All there ever is is a partial vacuum, and that partial vacuum--no matter how many inches of mercury--should always equalize in the system once the boiler goes down and the steam stops. 



One clever idea that we might be able to toss into this.  On one of Gerry Gill's old posts years ago, he mentioned venting Steve Pajek's system that they used to test things into the chimney.  Now, that isn't a bad idea--and it's basically "free" which means I like it.  If the partial vacuum gets low, it is possible this could help to re-establish it earlier in the firing cycle.  Hmm....



Right now, though, the biggest problem is figuring out whether it would work to put a check valve IN FRONT of the radiator vents, and whether the water retention issue MDN hinted at is a serious problem.  Having to put it behind the vents means having to buy all new Maid-O-Mist vents.  ROI gets a lot worse then.

mcsteamy

Coming up with a Check Valve

So far, it seems that we've determined at least in theory, it ought to work even with a gas burner.  Venting the mains can be done with a thermostatic trap vented to atmosphere through a swing check valve.  This (or some derivation) has been done on two pipe systems with good success. 



That leaves a few good practical questions.  First, is it really possible or practical to put the check valve in front of a radiator valve.  I suggested these valves:  http://www.usplastic.com/catalog/item.aspx?itemid=85451&catid=956 because they are cheap, and available off the shelf with a 1/3psig cracking pressure.  The devil's in the details, though, and I forgot about condensate drainage and the fussy little drip tube/tab that float vents have.  I think the condensate would drain (thoughts?), but there is nowhere for the drip tube.  Oops.  Are there problems with ripping it off?  The only other solution I can come up with is using a pair of street elbows in an "S" configuration, but that starts to add cost...



Second practical question is the cracking pressures.  Lower seems better.  Does the cracking pressure on the main need to be lower than the radiators?  That's tough using a 1/3psig part on the radiators.  I couldn't find an off the shelf, in stock part with anything lower.

MDNLansing

Different Idea

I have been thinking of an idea, but yet to test it, using steam ejectors to eliminate the chatter. The concept is simple. Fire the boiler up to 1 psi or slightly lower. Shutdown the boiler once steam volume is maxed out, then use a little steam from the system to draw a vacuum using a steam ejector. You might be able to take some steam in a main, reduce the pipe to 1/4" to increase the velocity, and shoot it through an ejector. This would draw a hard vacuum and reduce the condensate vacuum, thus eliminating the chatter caused by the pulsating natural vacuum. This is also a mechanical way of assisting the vacuum and doesn't need power or electric pumps.



This is mostly theory right now, but it will be tested in my lab shortly. I'll keep you posted, and any ideas about this are very welcome.

PMJ

One Pipe Vacuum

Thinking about trying to do this with a one pipe system makes me thankful I have 2 pipes and the luxury of a single vent for the whole system. Clearly a major advantage and easily worth the added up front installation cost. I don't envy anyone having to maintain vent devices of any kind on every rad.

Having said that, if I were stuck with a one pipe system (I didn't even know there were these 2 different kinds when I bought my place) it would be awfully tempting to go to the trouble of wiring all the rads so that I could run an electric solenoid valve on every one to vent them. Once installed the control would be amazing. Wired to a central PLC you could basically pick and choose which rads got steam when.

MDNLansing

Still Possible

You can still do the same thing now by turning the vent upside down.



The focus of this thread steps a little deeper by discussing ways to make a vacuum system better in the modern age.

ChrisJ

Sealing

The first thing I learned when trying to pull a vacuum on one of my monitor tops was any little leak at a fitting no matter how small made things difficult and even impossible.  I would be concerned about every valve steam seal immediately.

Besides that which is obviously fixable I would also be concerned about balancing.  I have TRVs as well as all different size vents in use due to the length of run outs and sizes of radiators vs the room they are in.  Right now my system is almost perfect running at 2 CPH and its amazing, but I can't see pulling that off under a vacuum.  The 2 or even 3 CPH sure, but the balancing no.

I guess if every radiator was still properly sized to the rooms (which my bedrooms are not and never were) and if all runouts were the same length or close to it, then sure.  But wouldn't there still be a problem with radiators getting steam one at a time as it runs down the mains?  There won't be any resistance to keep it from running right out to the radiators as it goes down the main.



I'm only commenting because I am interested in this and feel left out.  So if I sound negative I apologize for that.  Just thinking out loud.

mcsteamy

Chris,

I don't know exactly how it would work in practice, but in theory our

biggest challenge is typically getting steam to all of the radiators at

roughly the same time.  The vacuum at least would do that, and then fill

them one step at a time.  That's how a Paul system works, and quite a

few of those are still in operation and functioning.



Everyone used to say you could never run two pipe in a vacuum because you would have basically the same set of problem as are being claimed for single pipe.  Turns out, it works just fine on two pipe, and those that have done it, love it.  I bet it works fine here, too.  We just need valves.



I had hoped there was a way to make the check valves work in front of the existing vents.  A swing check would probably work, but most 1/8" check valves are ball or piston checks, and I have some serious doubts about condensate draining back when there is a 1/3psig present to push open the check.  The most I think about it, the more doubts I have.  I know they would work after the vents, but then you've got to buy all new Maid-O-Mist vents, too.  If you've got to do that, you might as well just try rigging them with a homemade gravity check valves. with a little rubber ball in a tube glued to the top or something...



You want to know why I think they really quit making vacuum vents?  As soon as one vent fails and is improperly replaced, the whole scheme falls apart... 

jumper

seal that system

Remove all vents,rads mains & risers, and seal the openings. Seal valve stems. Is the system hermetically tight? Evacuate the air. You now have a vacuum single pipe. Pressure now depends on boiler controls. Question is will all condensate drain? Or will it accumulate somewhere to make you want to break vacuums?