Vacuum boost retrofit, For 1pipe and 2 pipe steam systems

AMservices

A mechanically induced vacuum system that can be used to retrofit one-, two- pipe or mixed one-/two- pipe steam heating system.

Traditionally in steam systems the boiler would need to build just enough pressure to overcome the atmospheric pressure and force the air out through tiny holes in the steam air vents at the end of the steam mains (2-pipe system) or air vents on the radiators (1-pipe systems).

The air, that fills the piping and radiators, needs to be removed before the steam can move in to do its job, heating the living space. When steam pushed all the air from radiator and reached the vent, a pin sitting on top of a bellows expanded and closes the hole before the steam was allowed to escape.

With a vacuum pump, these air vents are no longer needed and are replaced with a vacuum lines in order to evenly evacuate air from the system and from each radiator. In the case with 2 pipe systems, the return piping can double as the vacuum lines.
Under vacuum the steam is being pulled into the system, instead of having to push its way through, you will be filling the radiators and heating your home faster.

When the system is completely filled with steam, the vacuum pump will shut off and the steam molecule will shrink 1,700 times its size back into water. This creates a naturally induced vacuum that will keep pulling steam from the boiler, long after the burner has shut off, steadily lowering the temperature in the system and keeping a balanced flow of heat moving towards the lowest point of pressure that is now the coldest rooms of the house.

By controlling the vacuum level, we can control the temperature of the steam in the radiators. With ball valves on the vacuum lines, we can control the path in which the air takes leaving the system.







Differently from traditional steam heating system retrofit into vacuum systems, vacuum pump is used mostly to ease boiler cold start. Once the steam starts working its way into the radiator it will compress the remaining air towards the vacuum lines, lowering the vacuum pressure and will then cause the vacuum switch to turn the pumps on, pulling the remaining air out of the system. If on a design day the boiler runs long enough to fill all of the radiators and the vacuum lines, a high limit switch will turn the pump off protecting it from incoming Steam.

Naturally induced vacuum do the most of the work to first push steam into radiators.

When weather is not cold, the thermostat set temperature is often achieved before positive pressure is formed in the system at lower radiators temperature. So, more comfort and no overheating is attained.

Immediate benefits of steam heating system retrofit include energy savings, better comfort, even heat distribution, quicker building heating from cold start, control of radiators temperature, soft comfortable heat supplied into radiators after end of heating cycle , no air hissing/hot condensate spitting from air vents, reduced water usage. Long time gains are: reduced corrosion, maintenance and flexibility to improve system further at your own pace.

Please, note that old steam boiler usually accumulate a layer of sediments working like additional seal on tiny holes at positive pressure. Under vacuum more leakage may develop when these sediments are pulled inside boiler by outside pressure.

Technology can be readily used to upgrade existing vacuum systems, reduce vacuum pump size and electrical load, eliminate steam steam traps on 2 pipe systems with orifices and balancing valves, simplify operation and schematic.

In new installations significant gains can be achieved via using plastic tubing and modern cast aluminum radiators, smaller piping and boilers with better designs more suited for this type of operation, with as many different styles of radiation. Fewer moving parts and points of failure, resulting in a longer lasting, more dependable heating system.

I've been working Dr. Igor Zhadanovsky on this technology for almost 2 years now. This is the 2nd system we have converted into a mechanically induced vacuum system with great success.

If you are in the Boston area with a central steam heating system, send me or @izhadano a message and we would be happy to give you an estimate.


Thank you for reading

PMJ

What is the sound level (db) on those pumps?

AMservices

56 dB (a)
But even if that's too loud for you the vacuum pump can be sitting anywhere in the basement you like

PMJ

> @AMservices said:
> 56 dB (a)
> But even if that's too loud for you the vacuum pump can be sitting anywhere in the basement you like

Bit of a concern when natural vacuum is 0db. Still thinking about it.

BTW, what if vent lines were plastic and all ran to a multiple solenoid valve manifold ( one valve for each rad) that you hooked up to a PLC. I would think you could then vent each rad independently as desired on any schedule. Start off natural and down the road attach a pump to the manifold if desired. Possible?

AMservices

The amount of money you spend on all the extra solenoid valves and controls would pay for the pump.
The plastic Airlines are absolutely possible and someday we will give that a shot for Shore.
Dollar for dollar the copper insulated tubing is cheaper per foot then the plastic alternative we would consider using

PMJ

I wasn't thinking the plastic tubing needed to be anything special or insulated. Like just nylon air line. Why insulated?

AMservices

PMJ said:

I wasn't thinking the plastic tubing needed to be anything special or insulated. Like just nylon air line. Why insulated?

Unless we had a Sure Fire way to ensure that no steam would enter that line, I would not attempt with nylon or vinyl tube.
As of right now we're still controlling the burner with a vapor stat set 2 to ounces cut out.
We want to still allowed the system to heat the house with its full potential on a design day.
So on a design day all of the radiators are going to be hot all the way accross and steam would be dragged down the vacuum line.

We probably could have done without the insulation. My thinking was reducing the amount of condensing happening in those lines.

We left the vacuum Main line uninsulated so any Steam entering it would give up it's Heat and condense before getting back to the pump.

AMservices

Jim_R said:

2 things.. The wire to the bottom screw of the vaporstat is bothering me



And the waterline in the sight glass looks like when I am under vacuum..No heat call..then I open the lwco and it tries to suck air into the boiler and dislodges the sediment in the system and kicks on the auto water feed etc .. but that is caused by introducing air into boiler..Other than that it stays clear.. Just wondering what the boiler was/just did when you took the photo..?

Jim

Thank you for pointing that out on the vaporstat.
That was after we first started the vacuum system and it satisfied the call for heat for the first time.
We flush the boiler and the wet returned since then.

jumper

Why do you need vacuum lines? Why can't I evacuate non-condensibles from boiler room connection(s)?

AMservices

With a two pipe system you don't need vacuum lines running to the radiators. The vacuum lines can be connected at the end of the dry returns.
Even with a vacuum pump we can't remove all of the air from the piping. At 15 HG there's still 50% air left in the system.
The steam will push the remaining air into the radiators, so if you're not taking the air out from the radiators, it will be trapped in the system.

gerry gill

I love it! Say hi to Igor for me, I met him some years ago in Chicago. The guy is brilliant. What fun you must be having working on projects with him!

AMservices

I am having fun! Trying to bring back old school technology and make it better.
This system is so easy to install, if it was a package system, a good team could have a boiler changed over in 1 or 2 days.
Extremely easy to balance. When you notice a radiator heating to quickly, you start closing the airline. In a 2 pipe system, you would throttle the supply valve.

jumper

AMservices said:

...
Even with a vacuum pump we can't remove all of the air from the piping. At 15 HG there's still 50% air left in the system.
The steam will push the remaining air into the radiators, so if you're not taking the air out from the radiators, it will be trapped in the system.

Unless you isolate boiler its water temperature limits vacuum you can pull. (15"Hg is about 180°F). When I used to evacuate & fill HHW systems 28" was easy.

Koan

@jumper - not sure what you mean. I get that water boils at 180 Deg F under 15"hg vacuum, but isn't that the idea to try to lower the boiling point?

AMservices

I'm a little lost as to what you're saying. Yes at 15 inches of mercury the boiler would be pumping out steam at 170 degrees.
The steam is still being generated from the boiler and will travel through all of the supply piping on its way to the radiator. If you pull a vacuum from the supply Main ( I don't know why we would need or want any more than 20") the steam will run right at that vacuum line. To protect the pump we have to have a high limit control to shut it off before the steam gets there. We would not be able to continue pulling the rest of the air out of the system if the pump is off. Because thie steam is going to fill the piping on its way to the radiator it will compress all of the air that's left in the system towards the radiators. If you're not able to remove the air from the top of the system, we can't heat the entire system.
Vacuum lines on the radiators ensure that we get the longest run time on the pump and will be able to evacuate all of the air from the radiator.

Koan

@AMservices I think I am agreeing with you. Evacuate the dry return on a 2 pipe system. Don't isolate the boiler, but maybe use a steam trap in line with the vacuum pump and solenoid so as to prevent frying either the pump or the valve.

Stat calls for heat, run the pump, stop the pump and close the valve at 10"HG, start the burner, cycle firing time

do i have this right??

AMservices

Koan said:

@AMservices I think I am agreeing with you. Evacuate the dry return on a 2 pipe system. Don't isolate the boiler, but maybe use a steam trap in line with the vacuum pump and solenoid so as to prevent frying either the pump or the valve.

Stat calls for heat, run the pump, stop the pump and close the valve at 10"HG, start the burner, cycle firing time

do i have this right??</blockquote
In this system we fire the boiler at the same time with the vacuum pump.
A vacuum immediately start registering on the boiler end. Anything under atmospheric pressure we're going to be boiling water faster so why wait to light the burner. It should work this way in any system that's tight with the right pumping capacity.
It takes roughly 5 minutes for the pressure in the system to go from 0 to 17 HG and the pump shuts off. As Steam starts moving in, it is compressing the air towards the vacuum lines lowering the vacuum pressure . When the vacuum switch senses 12 HG, it turns the vacuum pump back on. The vacuum pressure remains equal throughout the radiators via vacuum main. The pump will cycle like this until Steam has filled all of the radiators. If the system needs to run long enough that steam enters the vacuum lines, a high limit switch closes the solenoid valve and shuts the pump.

That's what worked for us, but there's too many different scenarios that may require a different set up.

jumper

That water boils at lower temperature is a bonus. To my mind the primary objective of a vacuum pump is to remove air. As PMJ pointed out steam will move faster. Plus air is a lousy heat transfer medium,especially compared to saturated steam.

Koan

@AMservices - Ironically, my first typed response was to fire the burner and start the pump simultaneously. My system gets nowhere near the pressures you mention. My vaporstat now cuts out at 8OZ positive pressure which is 1"Hg or about 14"WC. This is a 1928 residential Hoffman vapor system with 400 EDR of radiators, so it is relatively small. It appears your steam makes up the difference between 17 in Hg and 12 in Hg or about 2&1/2 psi - well above the pressure of 1/2 psi I run. because it is a lower pressure system I might be inclined to use a lower initial vacuum.

AMservices

Jim_R said:

> @AMservices said:

>

> Extremely easy to balance. When you notice a radiator heating to quickly, you start closing the airline. In a 2 pipe system, you would throttle the supply



2 pipe

OK .. I think I'm having a bit of trouble with following the one pipe and two pipe systems .. seems like 2 threads merged into one.. from a just regular guy perspective that is.

Is this the end product or are looking for feedback, thoughts, criticism as it seems to be a little quieter with postings than I would expect..

Just saying as there's no mention of specific inlet valves as the older graduated, modulate etc were designed for these systems vs Throttling a modern valve to achieve the same results .

2 pipe I believe you mentioned that no radiator traps would be needed ? I have a mix of check ball and modern , well more modern Dunham's which obviously are used to expell the condensates and closed to retain the heat but.. Coming back from a 6-7 degree setback for lack of a better word I could stand in the basement with my hand on the return and as soon as one of those check balls ... unchecks? I feel that return right away heating up .. Without any traps how would you control the steam getting in the returns and start filling the radiators with steam from the returns 2-pipe that is ?

The vaporstat of course would be mandatory .

And I know that steam is being used universally but we are talking more specifically towards the "vapor" as the lead into the system that wants to take the " path of least resistance".. so filling the mains first then the radiators..Still wouldn't excavate the radiators and heating closest to furthest kinda doesn't seem even..

You throw in different boilers , original pipe layout..

Condition of existing "hard ware " and most likely there there would be big fluctuations in converting or upgrading individual systems ? Not a kit you can sell at HD .. well maybe .. nowadays a starter kit..

On site time evaluation of existing system and jeez only knows what running through the walls, air leaks..

Not something you can really project..And estimate..



OK that's just some thoughts and I'm sure I made some errors..But I have impunity as I am not a engineer ,estimator,HVAC, and everyone I didn't mention by profession.



Like I said ..Not sure exactly if showing the future, present, past combined and in a few years it'd be like meeting Al Butz or that Penberthy guy that wasn't warned about the Foxes and Wolves on his way to market to sell his invention..



Do you have a patent application .. I think that maybe there's more than meets the eye here..



Just random notes entered though out the day..

Honestly... I appreciate the feedback and will answer any questions you have to the best of my understanding, but also results I've seen.
Your questions may make me think of something I haven't thought of yet.

Know this about me...
I am not an engineer, I am a mechanical contractor that has spent a lot of time talking with engineer's about the problems I run into.

As my friend Igor @izhadano would say
"You must think like vapor "
The vacuum pump is there to remove enough air that the vapor Steam can start moving in to compress the remaining air towards the vacuum lines so the pumps can pull the rest out and fill the system.
Vapor Steam is still looking for the lowest point of pressure. So as the radiators heat the rooms, the lowest point of pressure becomes the coldest room in the house and the vapor will begin to favor that radiator with the coldest metal, conveniently found in the coldest rooms of the house.
The system is working its best when the burner and the pump is off and the natural vacuum taking place pulling the rest of the heat from the boiler and sending it to the places it's most needed.
With 2 pipe systems, using orifices on the supply side of the radiator, we can control the flow of steam into the radiator and if properly sized, the radiator will condense all of the steam before it makes it to the other side.
If steam does make it to the other side and end up in the return (or vacuum line), it would lowered the vacuum pressure, close the vacuum switch, turn the pump on and be pulled in that direction, not allowed to find its own way out.
Part of preparing the system is conducting a pressure test and locating any major leaks and fixing them.
If a radiator isn't Heating as evenly as the others, that would be what you're looking for.

And yes, these are active patents at play here.

Koan

I think I mentioned my traps were all Hoffman 18s except for one Webster O2H, and a B&J 2CR crossover. I assume it is ok to leave these all in place correct??

AMservices

Koan said:

I think I mentioned my traps were all Hoffman 18s except for one Webster O2H, and a B&J 2CR crossover. I assume it is ok to leave these all in place correct??

You don't have to remove steam traps.
Steam trap maintenance is considered the biggest burden in maintaining a two pipe steam system. As long as the trap cannot open against the vacuum pressure in the returns, they can stay.
If you can use an orifice to Supply the radiator with as much Steam steam as it needs, then you don't need to trap steam. The radiator will condense the steam before it enters the return.
There have been several 2 pipe steam system that didn't use traps. this is 21st century model.
So if you don't need trap, why use them?

Koan

because I just replaced the cages in all 11 of them!

Jamie Hall

Um. A word or two about steam traps and orifices. Steam traps will close only if they see temperatures above about 200 F. Otherwise they will be open. If they are not subject to excess pressure differential, they last a long time -- 80 years is not unheard of. And orifices are pressure differential sensitive. If there is a moderate vacuum-- I see figures on the order of -4 or -5 psig mentioned -- the pressure differential across the orifice or steam trap may be somewhat higher than is desirable. Just a thought or two...

Also... I haven't seen it mentioned, but let's suppose for the moment that a high enough vacuum is employed to get the boiling point down around 140 or so. What are the stack temperatures if the vacuum is held there? Is there any chance of condensation in the stack or in the boiler? What happens to overfire draught and combustion efficiency?

izhadano

AMservices said
As my friend Igor @izhadano would say
"You must think like vapor "
===================================
I wish it was my saying ... actually, it's Dan Holohan motto.

AMservices

Koan said:

because I just replaced the cages in all 11 of them!

Good working steam traps are not a bad thing either.
I probably haven't been as clear as I should have been when stating that "steam traps can be removed".
Some people might be thinking about the mechanical vacuum systems that they see today ( leftover from yesteryears) and know that without the steam traps and those systems, steam would short cycle and prematurely shut the vacuum pump off before the system is filled.
This can be a real problem if you don't take the right precautions when designing a vacuum system.
Steam traps can be used to prevent short cycling. Id rather not use them because it's a moving parts that I don't want to depend on if I can do without.
That's why I know it's better two control the flow of steam into the radiator with a properly sized orifice, to keep the steam out of the return piping and far away from the vacuum pump.
I also think it's wiser using orifices rather than steam traps for the simple fact that steam traps will eventually fail. I think most of the have a 5 year life expectancy.
And when the day comes that the steam trap fails, I don't want steam taking out my pump.
Orifices are easy to install and change. They sit right inside the union fitting on the supply piping to the radiator. They don't fail, require zero maintenance and extremely cheap to make on your own.

Jamie Hall said:

Um. A word or two about steam traps and orifices. Steam traps will close only if they see temperatures above about 200 F. Otherwise they will be open. If they are not subject to excess pressure differential, they last a long time -- 80 years is not unheard of. And orifices are pressure differential sensitive. If there is a moderate vacuum-- I see figures on the order of -4 or -5 psig mentioned -- the pressure differential across the orifice or steam trap may be somewhat higher than is desirable. Just a thought or two...

Also... I haven't seen it mentioned, but let's suppose for the moment that a high enough vacuum is employed to get the boiling point down around 140 or so. What are the stack temperatures if the vacuum is held there? Is there any chance of condensation in the stack or in the boiler? What happens to overfire draught and combustion efficiency?

Your right about steam traps and I don't doubt there are ones that can last 100 years (under the right conditions). But there not all made the same. If there's a steam trap with a bellows thats saturation temperature will adjust to the conditions in the piping, then that what I would choose if I were trying to protect the pump with steam traps.
Your also right about orifices being pressure-sensitive.
Do know how many orifices I can make from as much metal I can buy for what a steam trap costs?
With the vacuum pump set up in a system, with no moving parts and the pressure controls that won't re-adjust themselves.
You set your pressure and depending on how evenly the radiator Heats in relation to the rest, you change the orifice.
A little more involved then adjusting the number dial on an air vent, but when it's done, it's done. No waiting or wondering when it will fail.
To get 140°F we need 24" Hg. I don't know this for sure, but I don't think the burner wouldn't run very long maintaining this. The pump would run longer then the burner.
24" is the upper limit with the pump in the picture and sustaining 24" could be difficult if you can't get the piping that tight and I'd say you need 4X the pumping capacity.
Also unless the heat loss of the home says 140 radiators will work, I wouldn't try it.

Jamie Hall

With regard to burner running times -- a BTU is a BTU, whether it is delivered by 140 F vapour or 215 F steam. The burner will run the same length of time in either case, bar small variations in boiler efficiency, unless the boiler is condensing, in which case the burner will run about 5 % less due to the recovery of latent heat of combustion. At the expense, however, of the boiler rusting out faster.

AMservices

Jamie Hall said:

With regard to burner running times -- a BTU is a BTU, whether it is delivered by 140 F vapour or 215 F steam. The burner will run the same length of time in either case, bar small variations in boiler efficiency, unless the boiler is condensing, in which case the burner will run about 5 % less due to the recovery of latent heat of combustion. At the expense, however, of the boiler rusting out faster.

I'm sure the original steam systems used to experience 24 hg on the regular
Those boilers were made out of cast,
It seems like they were able to handle it.
Or it could have been a problem for them and they equipped boilers with vacuum breakers to 20 HG.
Nevertheless, it's a problem that can be easily corrected by adjusting the operating controls.

Jamie Hall

So long as you keep the boiler either cold, or well above 140, you're right. Not a problem. Just don't try to run them for any length of time in condensing.

Koan

Makes me nervous to consider sucking so much air out of my 80 year old system. It has never seen more that 14 Oz of pressure.

Koan

@AMservices
If you don't mind, what do you use to do the switching based on vacuum - on at 17Hg, off at 12Hg. Also - what do you use for a high limit switch - is this a temperature sensor in the return?
Thanks.

mikeg2015

AMservices said:

Jamie Hall said:

With regard to burner running times -- a BTU is a BTU, whether it is delivered by 140 F vapour or 215 F steam. The burner will run the same length of time in either case, bar small variations in boiler efficiency, unless the boiler is condensing, in which case the burner will run about 5 % less due to the recovery of latent heat of combustion. At the expense, however, of the boiler rusting out faster.

I'm sure the original steam systems used to experience 24 hg on the regular
Those boilers were made out of cast,
It seems like they were able to handle it.
Or it could have been a problem for them and they equipped boilers with vacuum breakers to 20 HG.
Nevertheless, it's a problem that can be easily corrected by adjusting the operating controls.

Those old boilers had less efficient heat exchangers with much higher approach temps, so the flue gas temps were still well above 140F even if water temps fell below 130. The chimney in my 1903 home is lined with a fire brick. I assume because the original coal boiler flue gasses were in excess of 400F at times. At low fire however, when the coal bed died down, I could see some condensation occurring, and certainly near the top of a 40' chimney.

jumper

Big advantage of mechanically generated vacuum is air elimination. Less air makes it easier to move heat from boiler to terminals. How advantageous is operating steam at sub-atmospheric temperature?

So in olden days there were venturi vacuum generators but I don't think cut-out would be sub-atmospheric. Unless the steam producer was steam engine exhaust,and that's entirely a different variety of fish.

AMservices

jumper said:

Big advantage of mechanically generated vacuum is air elimination. Less air makes it easier to move heat from boiler to terminals. How advantageous is operating steam at sub-atmospheric temperature?

So in olden days there were venturi vacuum generators but I don't think cut-out would be sub-atmospheric. Unless the steam producer was steam engine exhaust,and that's entirely a different variety of fish.

You are correct.
First, the vacuum pump does a very efficient Job at reducing the pickup losses by exhausting enough air to have 5-10 HG pulling on the boiler when starting. We're making Steam within five minutes with a cold boiler. steam is at the radiators within 10 minutes and completely filled within 20-30 min.
When the system is filled with steam, a solenoid valve shuts keeping the air out and a natural vacuum takes place.
After the system satisfies the thermostat, the burner turns off and the natural vacuum will then keep pulling the steam from the hot boiler into the radiators that are condensing the most. Those radiators are always conveniently found in the coldest rooms in the house and mother nature takes care of balancing the system.

We first tried running the system by firing the massive boiler (wmg-7 connected to 580 EDR system) to the connected load. With this system i had to down fire the boiler 50%. Constantly holding 12 hg, never making pressure.
Very deceiving results occurred where the entire home was heating and all the radiators were hot. They were getting so hot, the owner shut the vacuum line off to the radiators he wanted cooler. The house was noticeably more balanced and comfortable, but the oil was being burned just as fast as before without the vacuum.
So by running under vacuum, throughout the call for heat, we were able to even distributed the btus, but the boiler never makes pressure, so never shut off.
It was like trying to drive a Mack truck with a V6.
I couldn't leave it running like that, so I increased the firing rate to give it pressure. But because boiler is oversized it short cycled .
So what I did to try and help the short cycling situation was I installed the anti short-cycle relay, so when the boiler makes 8 oz of pressure, the burner shuts off long enough for the system to fall back into a vacuum before firing again.
That's how I left at the end of last winter. I plan to go back before the next heating season to install a more appropriately sized boiler for this system.

My goal all along has been trying to reduce is fuel consumption while making a better balanced, more comfortable heating system.
Sometimes, for learning purposes, we need to make our own mistakes.
What I learned from this was
vacuum pumps reduce the pickup losses and help with the balance control.
Running a steam system with negative pressure is a pipe dream.
Steam systems are still #1 in my book.

PMJ

@AMservices,

The easy solution to the big boiler problem is to control it with timed cycles, not pressure. Find the total minutes of fire per hour needed to heat on design day. Divide that by 3. Keep the boiler off the rest of the time between the evenly spaced firings. Don't like 3 per hour? Spread it out however you like then. Lot cheaper than replacing a boiler at no loss of efficiency. In natural vacuum I barely touch atmospheric pressure for maybe 20% of the total time. With your pumps you never will.

Also thanks for confirming the automatic balancing power of vacuum.

jumper

Timing strategy was to over-heat building in wee hours so folks woke up toasty; and again in afternoon to come home from work or school to toasty. Tough call during extreme cold. When boiler was replaced with multiple small ones,one could leave one boiler going for other times. Authorities did not like manual operated flue dampers to isolate idle boilers. I wonder what pressure a boiler/burner at one third of EDR can achieve?

PMJ

jumper said:

Timing strategy was to over-heat building in wee hours so folks woke up toasty; and again in afternoon to come home from work or school to toasty. Tough call during extreme cold. When boiler was replaced with multiple small ones,one could leave one boiler going for other times. Authorities did not like manual operated flue dampers to isolate idle boilers. I wonder what pressure a boiler/burner at one third of EDR can achieve?

My timing strategy doesn't overheat. Boiler still turns off when the tstat is satisfied. Just spreads the calls for heat out so system sits in vacuum balancing itself most of the time. Ends up with much more even heat. How even the heat is can be rated by how long the calls are really. I actually have 3 different fire/wait timings in the program to cover the range of mild to extreme cold. There could be even finer adjustments than that if anyone wanted to.

P1385

@AMservices
This is a really interesting topic! Where exactly is the vacuum being pulled from in the system? On the dry return, a little before the water line? End of the main?

How is the water not pulled out of the boiler toward the vacuum pump? It would seem the suction would be higher on the return side of the boiler than at the boiler outlet, due to line losses. Add in the "pressure" the boiler makes and it would seem to shift the entire water line lower in the boiler and back up into the return lines a little.

jumper

P1385 said:

@AMservices
This is a really interesting topic! Where exactly is the vacuum being pulled from in the system? On the dry return, a little before the water line? End of the main?

How is the water not pulled out of the boiler toward the vacuum pump? It would seem the suction would be higher on the return side of the boiler than at the boiler outlet, due to line losses. Add in the "pressure" the boiler makes and it would seem to shift the entire water line lower in the boiler and back up into the return lines a little.

System I remember had no traps so static pressure was equal throughout when no steam circulated. Then it didn't matter where vacuum was sucked from.Vacuum can't lift water without pressure.

Actually some were more complicated. Involving rad in a cold place,"flash tank",and sometimes a device to "break" vacuum with steam to pressurize feedwater.

Goal is no air;low pressure is byproduct.

Koan

on @PMJ s system, there is no vacuum pump. There is an initial firing cycle that is a bit longer than the others and that cycle is the same as a non-vac system. once the first timed pre-heat firing cycle is completed a solenoid replacing the main vent closes so air does not return to the system. The steam condenses getting smaller and creates a natural vacuum. The next cycle, the steam does not have to push the air out again, the water boils at a lower temperature, and the vacuum on the return helps pull the steam through. A sensor is set to trigger the vent valve to open again once the return is marginally above atmospheric. Now all I need is the programming cable and @PMJ s TECO file and I will attempt the same! The vacuum is in the air cavity above the boiler water. The vacuum is created by closing the main vent on the return when the burner shuts off and letting the steam condense back into water. When the burner comes back on they system builds pressure and at 0.10"wc the solenoid opens to vent again. Steam hits the main vent, the vent closes, the solenoid on the downstream side of the vent closes again when the burner goes off. The burner is intentionally cycled on time to prevent overshoot and allow the creation of the vacuum between cycles. @PMJ - Am I getting this right this time??

PMJ

@koan,

Almost there. I do have a preheat sensor on the end of the main now that determines the length of the first cycle from colder start. Also, there is no vent at all on the steam main - only that one solenoid vent on the return. The traps are Mouat so never really closed so essentially the entire system is all under the same vacuum. Rads are condensing the fastest so there is very very slightly deeper vacuum in them than the mains which keeps the steam flowing forward during the burner off wait periods.

Happy to send you the file when you are ready.