Vacuum air vents on one-pipe systems

Ban

I don't understand why there aren't any manufactures who make air-vents for one-pipe systems that check the air. I am trying to understand what benefit there is to allowing the atmosphere back into the system after the radiators have condensed and so far I see none. I am not interested in creating an air-line or Paul system with forced vacuum. I am only interested in having the air exit and not return. Can someone please inform me why this is?



Thanks,



RB

ChrisJ

Vacuum

I also have wondered the same thing, however I believe there are two reasons.  The first is balancing, it would be impossible to balance a single pipe system operating under a vacuum.  The second reason is condensate, , I've heard there would be issues with getting condensate back but again I have not tried it and have very little knowledge on the subject.

Ban

I understand but,

I think the balancing could be an issue but wouldn't be an issue if you did it right. You could drill the orfice size to match the need of the radiator or simply add more holes. You could also add a slot in the cap where you could vary the amount of air by a valve, or lever.



Condensate: this should not be a problem at all. Water can move around freely in a closed system, right? Does it move around in a closed container such as a bottle? The water would simply displace the air.



Thanks for your reply, I want to discuss this more.

ChrisJ

Orifice

Drill an orifice in what?  If you put an orifice in the steam pipe condensate cannot leave.

Steam_Starter

Think of a straw...

If a one-pipe system prevents air from getting back to the system there would be a loss of water from the boiler due to the fact that it is "trapped" in the risers.



Think of a straw...my kids favorite thing to do at a restaurant...stick the straw in the drink, cover the end, then pull it out.  Water stays in the straw because there is no "air behind water" and it creates a vacuum.  And then at that point, the water that is "trapped" in the risers will prevent the steam from getting to the rads.  It will be running interference and turn the steam back to condensate as soon as the two meet, thus creating the dreaded water hammer.



Unless I am thinking of this wrong...which wouldn't be the first time...



JLG

Ban

Orfice

I was thinking on the exit of the vent after it passes the check.

Ban

Straw,

Except for the radiator nor the pipe will be completely filled with water to prevent flow. I think gravity would still bring it down being that it will not be occupying the entire diameter of the inner surface area of the pipe. I really want to believe this is possible.

ChrisJ

orifice no work

If the system holds vacuum at all it would balance throughout the system over time and all radiators would pull steam fast and what you get is what you get, in my opinion.



My system would be a nitemare as some runouts are 20' long while a few are only a few feet.

Ban

I have no idea

That is why I started this thread. I am really excited for the discussion. I also plan on testing it on a small system. I have an idea to make the vents but as steam starter stated I am a bit concerned about the condensate.



Theoretically, in a one-pipe system, after the entire system has filled with steam and the vacuum starts to occur will the condensate water be allowed to drain back to the boiler or not?

Pumpguy

Paul Systems

First off, please understand that I am a pump guy, and only deal with pumping equipment on steam heating systems.  While I know a fair amount about system piping details and fluid dynamics, my specialty is pumping equipment.



An interesting experiment would be to substitute the radiator's air vent for a Paul valve with a check valve on it's outlet air line side.  The outlet side of the check valve would be open to atmosphere.  A Paul valve, from what I understand, is a thermostatic valve that allows air to pass through it but not steam.  Again, if what I understand is correct, it operates like a thermostatic radiator trap on a 2 pipe system but is smaller to allow air venting to be uniform so you don't get overheating in one area, and underheating in another.



In a one pipe system, or 2 pipe for that matter, condensate always flows by gravity to the lowest point in the system.  This is true regardless if the pressure in the line is at pressure or vacuum. 



Vacuum in the steam lines, boiler, and radiators is a good thing in that you can make  steam at a lower temperature, and don't have to use steam pressure to push the air out again at the next cycle.  Also, you're not constantly introducing oxygen into the system so corrosion would be less of a problem. 



Operating at vacuum might have a negative effect on the boiler's pressuretrol, but that's something I do not know anything about. 



I'm probably displaying more ignorance than knowledge with this post so please take it accordingly and add corrections as appropriate.

Ban

Yes!

My thoughts exactly! But would it work? Could you use a Hoffman #3 (in this case) and get results? Has anyone ever tried it?

Charlie from wmass

Leaks are on reason for lack of vacuum vents

a pressure leak is easier to find. The Vacuum leaks around valve stems and other fittings allow air in and do not allow vacuum to form evenly. If you have vacuum you need to have it everywhere not just in one radiator. The straw effect occurs only if the whole system is not to sub atmospheric pressure. You could also have steam flashing to steam in the piping as the pressure drops. I also would not try this on a gasketed boiler. You could crash your boiler or radiators if you did a really good job of making a vacuum. You would need to include a vacuum relief valve to prevent too much vacuum.

ChrisJ

Vacuum

Charlie, wouldn't this be a concern on my EG series boiler just in normal use?   Figure if it ran for a good long time and all of my vents got good and hot, they wouldn't open for quite  awhile after shut down allowing a pretty strong vacuum.  Or,  are we talking a vacuum that would form after several cycles, each one squeezing a little more air out?

Mark N

Vacuum Vents

In the days of coal fired boilers the vents worked fine, They don't work with intermitttent firing. The coal burned for hours and you were able to get all the air out of the system. You can't do this with intermittent firing. The air that is left in the system expands in the vacuum and causes all kinds of problems. It is covered in LAOSH.

Ban

Coal

I am apprehensive that a vacuum system would only work in conjunction with a coal fired boiler. I would like more information on the air that is in the system and the problems it causes and why they are caused. If a manufacturer were to make brand new, well sealed vent that would act as a 1) float for water, 2) a vent to release air, and 3) a seal to prevent air from returning into the system--and they all functioned properly--why would there be a problem?

Ban

adjustable orfice

I should also add that the vent should have an adjustable orifice for sizing and balancing.

Mark N

Air

It is my understanding that all the air has to be removed from the system. The coal fired boiler allowed this to happen. With intermittent firing the boiler turns off long before all the air is expelled and the vacuum that forms from the collapsing steam closes the vacuum check. The air that is in the system expands to fill the vacuum. I would assume the if the vacuum isn't relieved and the vacuum checks are still closed the next time the boiler fires the flow of steam will be blocked by the air that can't get out.

SWEI

Coal, or

a modulating gas burner.



I'm still convinced this is a largely unexplored option for steam.

ChrisJ

What about

Producing a vacuum with a simple pump?



But at what point would running a vacuum pump start to eat up any savings? I'm not sure how much a vacuum you need, but an old refrigerator compressor could be used to pull a vacuum. You'd need to keep it lubricated some how though.

BobC

pump

Something like this might work for a long firing system. i don't know what kind of life it would have. From Surplus Center

SWEI

life

I used a 3,450 RPM Gast air pump to feed a pond aerator running 24x7 and we had to have it rebuilt in just a few months.  They're probably fine for intermittent duty.

Charlie from wmass

modern vents

have vacuum breaking built into it. even if they are hot they will not allow a vacuum to form. Yes EG boilers have gaskets between sections.

Ban

Interesting

So you think that even a slight vacuum could cause problems with the neoprene gaskets in the Weil-McLain boilers? Wouldn't the gaskets be able to withstand a negative pressure at the same percentage as positive?

Mark N

Pump

Since the vacuum vents are no longer made the whole point is moot. Paul vents are still made. Get the Paul vents add the air lines and a pump and you're in business.

Eastman

Vacuum, Modulation, and Efficiency

Vacuum seems to be the only way to modulate the output of steam.  There are no residential modulating steam boilers that I am aware of.  The only choice seems to be a mod/con with some kind of indirect coil.  If you can't lower the operating tempretures then you can't use a mod/con boiler for this purpose.  Achieving thermodynamic equilibrium appears to be the biggest major contribution to system efficiency in the residential market.

Ban

The whole thing is moot...

Correct. It is moot unless a vacuum vent is made or possibly using a Hoffman #3 without the line(?). There is no value to any of this if there is something that I am missing to cause this not to work. Fortunately vacuum on a one-pipe system hasn't been challenged very well. The largest negatives to this concept to date are:



1. Air not being fully purged from the line on fire-up and causing some kind of terrible pressure/balancing problem after the system starts to go into a vacuum



2. Gasket-style boilers not being able to withstand the vacuum pressure.



3. And vacuum air vents not being produced for one-pipe systems.



So the first one i'm not so sure about, the second one seems fairly unlikely as well however I did leave a voice-mail with Weil-Mclain yesterday asking that very questing, so we will see. The third one is a good point but not necessarily hard to overcome with simple hardware.



If there is anything missing outside of these three things on why this wouldn't work please post it!

jumper

tried before

Vacuum vents were sold before WW II. I think sometimes systems with them worked better but sometimes there were complaints so Hoffman stopped promoting them and eventually discontinued selling them. It is moot because nobody is going to try it again.



I agree with ChrisJ that you shouldn't need vents at all if the system is reasonably airtight. Just evacuate the air out with a pump or ejector. You can get a harder vacuum that way than using steam to push air through check valves.

Ban

Complaints to Hoffman

Do you know what kind of complaints there were? Why did people stop using them? I am not concerned on whether it will be produced in the future or not. My concern is will it work or not.



"I agree with ChrisJ that you shouldn't need vents at all if the system is reasonably airtight. Just evacuate the air out with a pump or ejector. You can get a harder vacuum that way than using steam to push air through check valves."



So with this you are saying that you would plug all of the radiators and main vents, then create a vacuum on the system and then close it and walk away?

Ban

WWII

Seems there were a lot of things that worked well prior to World War II.

ChrisJ

Nope

I think that vacuum pump would need to run constantly due to leaks in the system.  These arn't brazed or soldered hermetically sealed systems, you WILL loose vacuum no matter what.



I also think having small copper tubing run to each radiator in place of the vent hooked to a central pump that operates on boiler fire up could work too.  It would help create vacuum at the radiators first.

Mark N

1 pipe vacuum

I don't have any idea when they stopped manufacturing the vacuum vents. They most likely stopping making them because nobody was buying them. I would think people stopped buying them because they didn't work with oil or gas. If the dead men of 70 to 80 years ago couldn't get it to work. What has changed to make it work today?

Rod

Vacuum Air vents

Mark-  Good Point!

jumper

six kinds of steam heat

Somewhere on this site is an article with this name. It discusses the advantages of one pipe vapor. That's what it was called evidently. The DOA didn't have to balance heating because each room had a double hung thermostat.



As for sealing a system, if it is exposed you could gloop the joints. With modern chemistry there must be a way to block both air and steam. My friend installed steam heat systems without threaded pipe fifty years ago.

Eastman

The article...

The article seems to imply the chief culprit for oil and gas was the use of air vents to balance the system.  A vacuum break was recommended to restore the balancing function of the vents after each cycle.  It also mentions single pipe vapor systems would naturally balance with coal at the steady state condition.



Can modern TRVs be used in combination with the vents to balance a vapor system?

Gordo

I was on a job not long ago

that had Hoffman vacuum vents on the mains and all the radiators.  They were all working.  The system held a vacuum continuously and heated evenly and quickly. The customer did not want me to touch it (I didn't question that!).



I was there to replace the sightglass gaskets.  He knew they were leaking because the sightglass had bubbles in it due to the air being sucked in.  I had to get it real tight to stop the vacuum leak. He was most definitely NOT interested in a sightglass blowdown valve.



 Hours later, I was called back because the old sightglass had cracked. How did he know? It started bubbling again.

Vacuum leaks are a pain.

Charlie from wmass

not all dead men

were created equal in skill. I typed in a 3 paragraph answer as to what killed the steam vacuum air vent. It then deleted off the screen. To sum it up, lack of knowledge and skill of the people installing and maintaining heating systems is why the vents went away and why they will not come back. There are not enough people doing things right to sell enough vents for the industry to make a vent they only sell every decade or so.

Ban

No more to talk about

There you have it. Gordo witnessed it and by the sounds of his customer they were very protective of this rare breed. Now I have to test it and encourage you to do so as well! I will update.



Thanks everybody!

Ban

No more to talk about

There you have it. Gordo witnessed it and by the sounds of his customer they were very protective of this rare breed. Now I have to test it and encourage you to do so as well! I will update.



Thanks everybody!

Eastman

More talk...

Have you seen this article?



http://completewatersystems.com/2011/05/%E2%80%9Cvaporvacuum%E2%80%9D-dos-and-donts/



"Vapor/Vacuum" Do's and Don'ts  -- reprinted from CounterPoint Jan 95, vol. 2 issue 1



"Nowadays, however, most of us fire our steam boilers with gas or oil... ...This cycling creates problems in systems that have vacuum vents. The

vacuum quickly forms when the burner shuts off. Any air that doesn’t get

vented on the first cycle expands greatly, blocking the movement of the

steam “vapor” to the radiators. And because gas and oil burners shut

off completely between firing cycles, there’s no longer a hot bed of

embers to keep the low temperature water boiling. When you mix vacuum

vents with gas or oil, you usually wind up with uneven heat and

callbacks. You also wind up with condensate that doesn’t return quickly

enough from the system, and that can lead to water I level problems in

the boiler."



Automatic firing one pipe problem summary:

a)On/off automatic firing creates a hard and fast vacuum. 

b)The deep vacuum causes remaining air to expand greatly.

c)The greatly expanded air trapped in the system blocks the flow of heat from any residual boil.

d)Condensate tends to get trapped because air is not allowed back into the system.

e)If the system remains sub-atmospheric on the next cycle, the air vents will not operate and provide uniform distribution.



According to "Six Kinds of Steam Heat," one possible solution for "one-pipe intermittent vapor" was to add a vacuum breaker to prevent hard vacuums from forming in between firings.  Another was to break the vacuum at the beginning of each call for heat.  The noted disadvantage of these solutions, "It accentuates the familiar disadvantage of oil burner firing whereby heat is produced in great quantities for short periods, followed by long "off" periods."  I like the idea of breaking the vacuum on a call for heat, I don't see the downside over current practices.



Are there buffer tanks that could be adapted for sub-atmospheric steam production?

Other than the vacuum vents or possibly a pump, it seems like this is the missing piece to make "one-pipe intermittent vapor" work.  Break the vacuum at the beginning of each call for heat to provide uniformity, extend the firing cycle with an insulated buffer tank, extend the boil with the buffer.

Mark N

Parts

Richard where are you going to get the vacuum vents? Let us know how your test goes.

Gordo

Well, That Vacuum System was

definitely "one for the books".  But I advised the customer that he had a charmed system.  I suspect that if only one of the vacuum vents fails, the fairy dust will be released and it will break the spell.



I've seen other one-pipe vacuum systems, but with that one exception they were in failure spiral.  One radiator will heat normally one cycle or for several days. Then randomly stop heating.  Other radiators will start heating.  Then stop.  There is nothing for it but to replace the vents with current models.