Shouldn't the radiator vents close when the system starts to cool?

Underdog

I hear hissing from a newish Gorton #4 when the system starts to cool down. The air is going "into" the vent not "out." Doesn't that mean the above boiler piping is sucking steam (and heat) our of my warm radiator? If I flip the Gorton upside down the hissing stops. I'm a HO and the other radiator vents don't do this. This one radiator is at the far reaches of the system and the #4 lets it heat up evenly with the other radiators. When the boiler shuts off I want to keep the heat up in the radiator to heat the room, not down in the basement.

KC_Jones

That is normal function. When steam condenses it collapses (1700:1 ratio). When the boiler shuts down there is no more steam so what is there collapses and pulls air back into the system. This air isn't really cooling anything down. Since the boiler isn't firing there isn't a loss of heat. Once the steam collapses and becomes condensate it returns to the boiler and has given all it can give. The radiators stay hot for as long as it takes for the room to cool the cast iron. I assure you all your radiators are taking in air even if you don't hear it.

Paul48

Remember the finger on top of the straw trick? If that didn't happen you'd hold some condensate in the radiator and associated piping.

BrianT1077

I get the same results at my farthest radiator when my boiler shuts down. Only difference, that radiator never heats, the shutoff is fine and the pipe never gets warm. Still trying to figure that one out. Has a new vent too!

Fred

BrianT1077 said:

I get the same results at my farthest radiator when my boiler shuts down. Only difference, that radiator never heats, the shutoff is fine and the pipe never gets warm. Still trying to figure that one out. Has a new vent too!

Sounds like there may be water sitting in that radiator run-out or in the radiator. Check the pitch of both.

BrianT1077

@Fred, I will check into that, thank you!

Jack M

great analogy.

Underdog

KC_Jones said:

That is normal function. When steam condenses it collapses (1700:1 ratio). When the boiler shuts down there is no more steam so what is there collapses and pulls air back into the system. This air isn't really cooling anything down. Since the boiler isn't firing there isn't a loss of heat. Once the steam collapses and becomes condensate it returns to the boiler and has given all it can give. The radiators stay hot for as long as it takes for the room to cool the cast iron. I assure you all your radiators are taking in air even if you don't hear it.

Now I understand. Very helpful.

johnnyh13

no when steam turns back into water valve opens to allow it to drain back. think of holding your finger over a full straw with water it wont come out tills air

Underdog

I'd be curious to know how much inefficiency in steam is attributed to the air being drawn back through the vents, back through the radiator, back through the basement piping, and to the boiler. If those radiator vents stayed closed tight and instead the main vents in the basement opened to allow air in, wouldn't the radiators stay warmer for a longer period of time. (waiting for the next heat cycle).
How does the "mini-steam" system function in this respect?

PMJ

Paul48 said:

Remember the finger on top of the straw trick? If that didn't happen you'd hold some condensate in the radiator and associated piping.

Does this really apply here? The straw trick requires the bottom end of the straw(pipe) to be completely full of water to work. No such condition ever exists in a radiator or riser - or we get horrible hammer. I don't think a drop in pressure below atmospheric on top of any water in the bottom radiator as the steam collapses can keep gravity from taking it back down the mostly open pipe and returning it to the boiler.

Jamie Hall

Underdog said:

I'd be curious to know how much inefficiency in steam is attributed to the air being drawn back through the vents, back through the radiator, back through the basement piping, and to the boiler. If those radiator vents stayed closed tight and instead the main vents in the basement opened to allow air in, wouldn't the radiators stay warmer for a longer period of time. (waiting for the next heat cycle).
How does the "mini-steam" system function in this respect?

This, of course, is the intent behind various steam systems which were able to hold a vacuum, and many of the vapour systems in the coal burning era were able to do so. These systems -- with a few exceptions -- had vents (including the main vents) which stayed closed tight against a vacuum; the vents were essentially thermostatic check valves, which would open below a certain temperature to let air out, but would not let air back in, and would close when the temperature rose and steam hit them.

Note that these were all two pipe systems, operating on very low pressures.

With a coal fired boiler, the effect was that they would continue producing steam at the boiler even when the fire was damped down, as water boils at a lower temperature under a vacuum. This kept heat going to the radiators.

The radiator, I would point out, gets its heat from the condensation of steam inside it. Without steam, it will cool down. The only reason that it will stay warmer longer if there is a vacuum present is that there may still be steam from that damped down fire; the residual heat in a boiler is not sufficient to have any real effect.

In modern systems if there is enough modulation available at the boiler(s) to produce steam at subatmospheric pressures -- a "vacuum" -- there would be some point to it. @vaporvac with her staged boilers, is doing something of this nature.

The gain in efficiency is, I'm sure, there, but I suspect if of being small enough to be hard to discern in the noise. It would not come, however, from avoiding drawing the air into the radiator or the piping -- that would a miniscule difference -- but from being able to run the boilers at a lower temperature for a longer period of time, rather than cycling them, in much the same manner as a mod/con boiler gains efficiency in an hydronic system by running all the time at a lower water temperature.

Where a real difference can be made, however (in my view, anyway!), is in assuring that there is adequate venting so that the air drawn back in on cooling is able to leave again very very quickly when steam is raised in the next cycle.

Here there is a balancing act. Steam vents which close on vacuum are still available without much difficulty. However, their capacity is much smaller than some of the big "normal" vents, such as the big Gortons. If your system is tight enough to hold a really good vacuum for a significant time -- on the order to a few hours -- then these may well be worth the effort, although you may need more of them than you would to vent the same system properly with Gorton or similar vents (depending entirely on how tight your system is).

Take a look at the descriptions in The Lost Art -- or in the history pages of this site -- for some of these systems.

I should add that there were also systems which used a vacuum pump to withdraw air from the system at the start of a cycle. Some of these had vacuum connections to each radiator and could be piped in a manner very like a one pipe steam system, but without radiator vents with the vacuum lines taking their place. They worked very well, too -- but in my view the complexity of the vacuum pump makes them unnecessarily complex.

ChrisJ

Paul48 said:

Remember the finger on top of the straw trick? If that didn't happen you'd hold some condensate in the radiator and associated piping.

Perhaps,
Except that those huge pipes will eventually let air in and that would let the tiny bit of water out. There's no water seal, so to speak.

ChrisJ

Underdog said:

I hear hissing from a newish Gorton #4 when the system starts to cool down. The air is going "into" the vent not "out." Doesn't that mean the above boiler piping is sucking steam (and heat) our of my warm radiator? If I flip the Gorton upside down the hissing stops. I'm a HO and the other radiator vents don't do this. This one radiator is at the far reaches of the system and the #4 lets it heat up evenly with the other radiators. When the boiler shuts off I want to keep the heat up in the radiator to heat the room, not down in the basement.

As everyone has said, this is normal.
When my system runs for long periods like during a recovery the radiator vents often hiss fairly loud as air is sucked in when the boiler shuts down.

It's just the nature of the beast and isn't hurting anything.

Paul48

I'm sorry...I understood him to be speculating on the merits of a sealed system. One that didn't draw air in from anywhere in the system.

ChrisJ

Paul48 said:

I'm sorry...I understood him to be speculating on the merits of a sealed system. One that didn't draw air in from anywhere in the system.

That's something I'd love to build one day. A steam system that is 100% hermetic and a deep vacuum is pulled before filling with water and perhaps an inert gas to get the pressure where you want it.

No corrosion, no vents etc. A steam system with no moving parts that runs at 140-160F.

Jamie Hall

"Nature abhors a vacuum". I doubt. I very much doubt. That it is even possible -- for the best of our folks -- to build a steam system which will hold a vacuum indefinitely without a vacuum pump.

ChrisJ

Jamie Hall said:

"Nature abhors a vacuum". I doubt. I very much doubt. That it is even possible -- for the best of our folks -- to build a steam system which will hold a vacuum indefinitely without a vacuum pump.

You do realize there are plenty of guys on this forum, best or not, that build air tight refrigeration systems all the time right?

I can assure you many guys here given time and money could easily build a hermetically sealed steam system that will never need a vacuum pump other than the initial pull down. Construct it of steel and copper and silver solder or weld all joints.

Jamie Hall

ChrisJ said:

Jamie Hall said:

"Nature abhors a vacuum". I doubt. I very much doubt. That it is even possible -- for the best of our folks -- to build a steam system which will hold a vacuum indefinitely without a vacuum pump.

You do realize there are plenty of guys on this forum, best or not, that build air tight refrigeration systems all the time right?

I can assure you many guys here given time and money could easily build a hermetically sealed steam system that will never need a vacuum pump other than the initial pull down. Construct it of steel and copper and silver solder or weld all joints.

Oh well... yeah, I suppose. That would be quite the system... Now that I think about it, if one wanted to do that (it wouldn't come cheap...) one could -- and then, why not use something other than water for the heat transfer liquid? With a more reasonable boiling point at a more reasonable vacuum. Be interesting to research that -- though I think the expense just might be a bit daunting for the average homeowner!

ChrisJ

Jamie Hall said:

ChrisJ said:

Jamie Hall said:

"Nature abhors a vacuum". I doubt. I very much doubt. That it is even possible -- for the best of our folks -- to build a steam system which will hold a vacuum indefinitely without a vacuum pump.

You do realize there are plenty of guys on this forum, best or not, that build air tight refrigeration systems all the time right?

I can assure you many guys here given time and money could easily build a hermetically sealed steam system that will never need a vacuum pump other than the initial pull down. Construct it of steel and copper and silver solder or weld all joints.

Oh well... yeah, I suppose. That would be quite the system... Now that I think about it, if one wanted to do that (it wouldn't come cheap...) one could -- and then, why not use something other than water for the heat transfer liquid? With a more reasonable boiling point at a more reasonable vacuum. Be interesting to research that -- though I think the expense just might be a bit daunting for the average homeowner!

I thought about the liquid as well but I'd still want to pull a strong 500 micron or greater vacuum before filling. This would prevent any corrosion.

I see the system as essentially a huge multi-headed heatpipe.

Paul48

It certainly sounds good....but then don't you have less latent heat in the steam you created at 140-160*? Do you have to use that as a multiplier for your edr?

KC_Jones

Instead of just sealing it up tight, what if you used a vacuum pump and modulated the vacuum. This would allow you to vary the steam supply temperature, add a modulating burner and connect it all to an outdoor reset control and keep dreaming. Hey @MarkS I think I have a new project for you! lol The payback would be zero, but it would be an interesting experiment.

Steamhead

Getting back to the original post, another thing to check for is uninsulated steam piping. If steam condenses in uninsulated pipes, it will create even more vacuum after the boiler shuts off, and pull steam out of the radiators even faster.