Why no vacuum on single-pipe?

Jakek

On single pipe steam systems, why are the vents not designed in such a way to only release and only below ~212f so that a vacuum forms upon the first cycle?

Presumably that would allow for a lower boiling point and more efficient system. Even if the vacuum was broken, it would be re-formed upon the next cycle.

This isn't done so there must be something I'm missing.

Jamie Hall

The vacuum would form at the end of the cycle, not during -- unless you had an ejector or vacuum pump (such as the Paul system).

Jakek

@Jamie Hall Yes, I understand that. But after the first cycle the vacuum would remain and thus use less BTUs to generate steam and move it through the system upon the second and future cycles, correct?

EBEBRATT-Ed

When burning coal they had vacuum air vents because the fire burned all the time. When these systems were converted to oil and gas and the burner cycled the vacuum vents didn't work so well. I don't think they are made anymore

ethicalpaul

I’ve looked into this a bit and thought about it a lot.

Hoffman at one time I think made vents that would hold vacuum. @Gordo even has some for sale I think.

I have an itch to buy a mini-lathe for the express purpose of having fun trying to make a very low cracking-pressure check valve for each of my radiators, but there are two problems:

1. there’s just not much vacuum. When my small system is full of steam at 1.5psi (which takes over an hour of runtime to achieve) then the cycle ends, I only see about 30 inches of water column vacuum (a bit over 1 psi). My MoM vents will hold this for about 3 minutes then one of them opens and the pressure rises over the next two minutes and then it’s at 0. It’s just not very much.

This next issue I recently came up with:

2. let’s pretend it’s a lot of vacuum and I have a good check valve on each radiator and my main vent. What then?

well vacuum will indeed form. It will start out greater in each radiator (and in the boiler) due to the greater volume there. But it won’t stay there! The pressure throughout the system will equalize very quickly like within seconds.

So then you have low pressure throughout the system. The same pressure. So even if that lower pressure will coax additional steam out of your cooling boiler, where will it go?

Steam always goes to lower pressure Dan teaches us. Which means it will go nowhere.

it’s not like there is some low pressure zone in each radiator sucking in this 210 degree steam. 

So sadly I think there’s nothing to it. And I have my doubts about its actual benefit in a two-pipe system.

DanHolohan

And then there's this: https://heatinghelp.com/systems-help-center/a-new-look-at-vacuum-heating/

AMservices

https://forum.heatinghelp.com/discussion/161394/vacuum-boost-retrofit-for-1pipe-and-2-pipe-steam-systems
   Here is an example of Igor Zhadanovsky system. 

mattmia2

ethicalpaul said:

I
Steam always goes to lower pressure Dan teaches us. Which means it will go nowhere.

it’s not like there is some low pressure zone in each radiator sucking in this 210 degree steam. 

So sadly I think there’s nothing to it. And I have my doubts about its actual benefit in a two-pipe system.

Why wouldn't the steam condensing in the radiator lower the pressure and pull more steam in the same way it does at or above atmospheric pressure inside the system?

AMservices

Steam condenses making a naturally induced vacuum. That happens above or below atmospheric pressure. 
 As long as air can not infiltrate, or the radiator isn't cut off by a TRV, steam will continue to fill the places its been, as long as steam is still being produced. 
@ethicalpaul The naturally induced vacuum becomes the low point of pressure. That's why vacuum systems are so good at self-balancing. The coldest rooms, condense more steam making a stronger vacuum. In other words, making the lowest point of pressure. 

ethicalpaul

mattmia2 said:

Why wouldn't the steam condensing in the radiator lower the pressure and pull more steam in the same way it does at or above atmospheric pressure inside the system?

Because the pressure would equalize in the overall system instantaneously. The Igor system shows this because it requires a vacuum pump and is no longer 1 pipe

it’s not the same as our systems because the boiler is constantly making steam pushing everything to the radiators. Yes there is some vacuum from the condensing but not enough to make a difference IMO. Ask Igor why he needed a vacuum pump to pull the steam to the radiators. It wasn’t just for fun I think

AMservices

The pressure throughout the system is not completely equalized until the temperature throughout the house is equalized. 
It depends on how tight one can get the piping to achieve lower vacuum levels for longer durations at the end of the cycle. 8-15HG is not un heard of. 
The vacuum pump can be controlled to run for X amount of minutes at the end of a cycle to help out those leaking system or it can be turned off with the boiler and let the natural vacuum take place.  
Yes technically a 1 pipe system with air lines can be considered a 2 pipe system. 2 pipes are better then 1 and air lines are a way more cost effective way to convert a single pipe into a 2 pipe. 

ethicalpaul

Why does the pressure in the system care about the temperature in the house?

I would like to see how 15 HG could be created in a steam system without a pump. 

AMservices

ethicalpaul said:

Why does the pressure in the system care about the temperature in the house?

I would like to see how 15 HG could be created in a steam system without a pump. 

I want you to imagine a steam system completely filled. The boiler has just started making a few ounces of positive pressure. Thermostat satisfies, boiler turns off and all the steam starts to condense. But it's condensing faster in the colder areas outside the boiler room.
Imagine there's no leaks in the piping or a way for air to get back in. 
The needle on the pressure gauge drops to 0, but then, it keeps slowly dropping on the negative pressure side. This Doesn't happen fast because as the gauge is dropping, so does the boiling point and the boiler is still making steam to replace the steam condensing in the radiators. 
Steam will continue moving into the system because steam is condensing in the radiators, in the rooms away from the boiler, where it's colder. Steam is still moving towards the lowest point of pressure because the vacuum is deeper in the radiators. 
Now all the radiators are not in the same room as the thermostat. A corner room maybe cooler then other.
THE RADIATORS IN THE COOLER ROOMS WILL CONDENSE STEAM FASTER. 
that makes a deeper vacuum then in the rooms with even slightly warmer temperatures. It is a naturally self balancing system. It can do this because the difference in temperature between the rooms will make a lower pressure,  in radiators, in the colder rooms. 

ethicalpaul

I don’t have to imagine very much of this, I have very accurate gauges at the boiler, on a riser, and at the radiator in my office. In my office are two gauges, one hooked up “backwards” to show how deep the vacuum goes.

I’m sure this effect is happening but no one would notice it.

EBEBRATT-Ed

@AMservices explained it well.

When the system shuts off on the thermostat consider the radiators condensers (even though they always are). If the system is full of steam with no way for air to get in the radiators condense some steam forming a vacuum in the radiator. This pulls steam toward the radiator. As the vacuum forms more water in the boiler boils off even without the burner running because the pressures has dropped and now the steam is at a lower temperature and this continues at a slower and slower rate as the system cools.

I would think you would need all the piping insulated for this to work

One cubic foot of steam is 1700 x the volume of 1 cubic foot of water will make quite a vacuum

AMservices

@ethicalpaul are you trying to make a vacuum? 
Your not going to see much if any if you have air vents opening all over the system. 

mattmia2

The most important part would be to get most of the air out of the system. If there is a significant amount of air in the system it will simply cool and lower the pressure slightly, it won't condense and create a large pressure drop that will produce more steam.

PMJ

I've posted this before - attached is what the system pressure looks like cycling 1.5-2 burns per hour with natural vacuum peaking around 5 inches Hg +/-.

It is just as @AMservices says. When the burner goes off the system pressure drops below zero steadily as the steam condenses. The radiators remain the lowest pressure points in the system unlike open vented where they almost instantly become the highest stopping the steam flow into them. Instead, they continue to draw steam from the mains with the burner off and and new steam formed from the residual heat in the boiler continues to flow. This flow favors radiators in the colder areas because steam condenses faster there. This balancing effect each and every cycle is very significant. It has completely eliminated upstairs/downstairs differences in my house which prior to vacuum were very large. Not to mention this balancing is completely automatic adjusting itself to changing sun and wind conditions.

In colder weather with multiple cycle calls with burns of 9-10 minutes and waits of 17-18 minutes steam will reach radiators 2 minutes or so before all the vacuum is gone on new burns so there is additional natural balancing on the front end of the cycles too. Steam production starts much earlier in the boiler from fire in the low pressure too - full boil in 20-30 seconds after an 18 minute wait.

I have run this way for many years now. Pumps would obviously enhance the effects, but I can say without question that even at 5" Hg it is a big improvement. Natural vacuum operation is also the lowest noise method. Not a large efficiency improvement at this vacuum level but probably in the high single digit % range somewhere. I do it primarily for the comfort improvement.

Quite honestly if I had a one pipe system I'd be figuring out how to pull the air lines. Or maybe just wires to install tiny solenoid valves and cheap temp switches to close them when the steam got close. Those would be zero cracking pressure.

ethicalpaul

AMservices said:

@ethicalpaul are you trying to make a vacuum? 
Your not going to see much if any if you have air vents opening all over the system. 

I’m making a vacuum. It holds for about 3 minutes then, yes, the vents start to open. 

Danny Scully

Speak of the devil @ethicalpaul. While it’s not exactly 15, it’s close! For fun, I installed ball valves on all my vents. System pulled a vacuum today for over an hour and was continuing to get deeper. I decided to stop because, we’ll, it’s Valentine’s Day 😉. 

AMservices

Danny Scully said:

Speak of the devil @ethicalpaul. While it’s not exactly 15, it’s close! For fun, I installed ball valves on all my vents. System pulled a vacuum today for over an hour and was continuing to get deeper. I decided to stop because, we’ll, it’s Valentine’s Day 😉. 

Funny. I was just about to suggest @ethicalpaul try that same experiment. 

Dan gets an A+ on the tight system test. 

PMJ

One pipe systems will naturally pull deeper vacuums than two pipe as steam fills a higher percentage of the total system volume. Its collapse has a much more dramatic impact. 

ethicalpaul

You know what’s hilarious, you guys? This happened this morning before your posts 😂

Is that gauge inches of mercury,  "Danny Scully" ?

ethicalpaul

Dammit how did I order 1/4” valves?! 🤬

Danny Scully

In-hg @ethicalpaul. Here’s an example of one of the rads. 

ethicalpaul

Yep I have two of mine like that already 😃

My wife got sick of rotating the vent in the bedroom so I put a valve on that one for her.

mattmia2

I isn't like they ship on sunday, probably not too late to call them and change it.

ethicalpaul

Yeah they are great, I canceled that item

Jakek

Thanks everyone for this thread. Interesting stuff.

ethicalpaul

So I've pretty much decided I'm buying a small lathe for fun. I'll let you all know if I can fashion a very-low-cracking-pressure check valve for installation on one-pipe radiators.

Motorapido

ethicalpaul said:

So I've pretty much decided I'm buying a small lathe for fun. I'll let you all know if I can fashion a very-low-cracking-pressure check valve for installation on one-pipe radiators.

Great to hear. You can start a side business, and I'll be your customer. I owned a Harbor Freight 7x10 mini lathe for years, and a HF mini mill. I used both extensively to fabricate parts made of unobtanium for various 1950s and 1960s vintage motorcycles that I restored. They are certainly not pro quality metal shop tools, but support and advice from various mini lathe forum enthusiasts is helpful in learning to extract top quality work from these small metal shop tools.

CLamb

ethicalpaul said:

So I've pretty much decided I'm buying a small lathe for fun. I'll let you all know if I can fashion a very-low-cracking-pressure check valve for installation on one-pipe radiators.

Before you do that search around for one already manufactured. I would be surprised if you don't find one. It's unlikely that a steam radiator is the manufacturer's intended use however.

ethicalpaul

Yeah, I have searched the internet high and low for over a year for such a thing. I can't find it. I even bought a couple that were purported to be "low cracking pressure". But there's low and then there's "residential steam system low", so even these were ridiculously high for our needs.

Plus, what's the fun in that?

SteamingatMohawk

@ethicalpaul "One pipe systems will naturally pull deeper vacuums than two pipe as steam fills a higher percentage of the total system volume. Its collapse has a much more dramatic impact. "

I'm having difficulty understanding this comment. Can you explain it further?

mattmia2

Maybe it needs to be more like a diaphragm over a large seat (so that the very low opening pressure is over a large area and can multiply in to a reasonable amount of force) than what one would conventionally think of as check valve construction.

ethicalpaul

SteamingatMohawk said:

@ethicalpaul "One pipe systems will naturally pull deeper vacuums than two pipe as steam fills a higher percentage of the total system volume. Its collapse has a much more dramatic impact. "

I'm having difficulty understanding this comment. Can you explain it further?

no, I can't because I didn't make it-- @PMJ did

And I am too ignorant of 2 pipe systems to understand it either

ethicalpaul

mattmia2 said:

Maybe it needs to be more like a diaphragm over a large seat (so that the very low opening pressure is over a large area and can multiply in to a reasonable amount of force) than what one would conventionally think of as check valve construction.

Definitely something interesting will have to be done. The current design in my head uses gravity for the spring and I hope that won't be too much!

mattmia2

I assume you have tried this sort of thing:

https://www.mcmaster.com/2987K38/

mattmia2

So, I have a more fundamental question here. How do you let the condensate that inevitably ends up in the vent drain back in to the radiator if there is a check valve preventing anything, air or water, from returning to the radiator? I guess you could use a seam trap then put the check valve on the outlet of the steam trap instead of using a conventional 1 pipe radiator vent.

PMJ

ethicalpaul said:

SteamingatMohawk said:

@ethicalpaul "One pipe systems will naturally pull deeper vacuums than two pipe as steam fills a higher percentage of the total system volume. Its collapse has a much more dramatic impact. "

I'm having difficulty understanding this comment. Can you explain it further?

no, I can't because I didn't make it-- @PMJ did

And I am too ignorant of 2 pipe systems to understand it either

The level of vacuum created is directly related to the percentage of the total air removed from a system. Two pipe systems have a higher percentage of total system volume in piping that never sees steam. In operation the steam then pushes out a smaller percentage of the total air in the system in two pipe than one pipe. So when the steam collapses a larger void as a percent is created in the one pipe system and a deeper vacuum results.

ethicalpaul

mattmia2 said:

So, I have a more fundamental question here. How do you let the condensate that inevitably ends up in the vent drain back in to the radiator if there is a check valve preventing anything, air or water, from returning to the radiator? I guess you could use a seam trap then put the check valve on the outlet of the steam trap instead of using a conventional 1 pipe radiator vent.

I'm planning to put the check valve after the vent