Vacuum Breaker for One-pipe Steam?

AdmiralYoda

Got a quick question on my one pipe counterflow steam system. My boiler is oversized so it usually cycles on pressure. 10oz cut out, 6oz differential. When it cuts out as the steam condenses in the rads and pulls a vacuum. Normal.

Problem is the radiator vents sound like a big turbo spooling up. And when your boiler is oversized it might cycle every 2 min or less! I know this is normal, but I'm looking to reduce this and a vacuum breaker sounds like a good idea.

Any reason not to do this solely just for reducing the vacuum noise? And bonus question...could one be installed on a main vent tree?

I'm thinking Barnes and Jones.

delcrossv

Don't see why not as long as it closes on lack of vacuum.. Main vent tree is as good a spot as one could hope for.

ethicalpaul

Change out the loud vent for one that holds vacuum better. Hope the loudest one ends up being your main vent.

Also, I’m surprised you’re getting vacuum during pressure cycling. When my old boiler cycled, it would start building pressure before it went negative if I recall correctly 

EBEBRATT-Ed

actually the vacuum is good the rads will keep heating as the steam cools giving you more heat.

But the vacuum needs to go before the burner fires again as it will hold condensate in the system.

Usually the vents will take care of this.

Tunstall has good steam vacuum breakers, you can also use a swing check valve (a good one with the gate on a 45 deg angle) not a up and down gate. They are called Y pattern check valve

AdmiralYoda

@ethicalpaul I have a soft limit on my boiler. At 6oz my rads are full so I have a pressure switch and a timer to turn off the boiler at 6oz and take stay off for a programmable amount of time, usually 5 minutes. This gives the radiators time to release some heat into the room before the boiler cycles on pressure. So that is why it pulls a vacuum every 5 min or so as the rads are allowed to cool.

I'm using Maid-o-Mist air vents on all the rads because I like swapping the orifices to fine tune the venting. Anyone know of a good quality vent that is better at holding vacuum?

PMJ

You need a control that never lets your boiler run long enough to build pressure in the first place and also never lets 2 consecutive burns be that close together. Everything gets better( and quieter) then, unless your system is badly unbalanced and requires header pressure to get steam to some places at all. In systems where steam will arrive at all radiators at about the same time no header pressure beyond an ounce or two is ever required for heating.

I keep saying this - when the fire was continuous obviously the radiators were never full and pressurized or the occupants would have been roasted alive. I keep asking what is the point of filling them to pressure now? Just because the boiler is big doesn't mean we have to let it happen. My system used to do this. I don't let it anymore.

cross_skier

I experienced noisy vents from vacuum cycling on my new vaporstat after my install many years ago..  I was worried that my new insulated returns were a contributor.  I wrote @DanHolohan  as I was really fortunate to find his articles in trade journals at a local university library. He was kind enough to reply and wrote it was ok to put a 1/2" swing check valve on my header, that my insulated returns were a good thing.  The check valve and downfiring the boiler 10% solved the problem.

After adding a lot of venting on mains and risers I no longer needed the check valve no matter the firing rate. I must have brought the wrong one, it stuck close.  The only thing that changed over the years was that I added a lot of venting for three good size mains and risers and swapped to smaller radiator vents.

ethicalpaul

Ahh yes I forgot about your timer but that's partially because you tricked me

You said you were cycling every two minutes or less!

In my experience, the MoM or Gorton vents hold a vacuum pretty well.

I would set that timer for longer. Are your radiators getting fully hot before it starts cycling on pressure?

PMJ

Where did I say 2 minutes? Mistake if I did. My consecutive burns typically 7-9 minutes with waits in between burns 15-20 minutes depending on the weather.

My radiators never fill so there is no pressure ever. I start a timer when steam arrives at my garage radiator fill pipe (the most remote radiator in the system) and it stops the burn 210 seconds after that. Radiators all only partly full at that point - no pressure ever. This is plenty of radiator fill to heat the place. Firings get closer together by a few minutes when it is colder changing the total BTU/HR delivered. Self adjusting.

ethicalpaul

sorry not you PMJ, I meant Admiral Yoda. I was suggesting he increase his wait timer from 5 minutes because in my mind 5 minutes is too short because there is still lots of heat in the radiators that can be given up before bothering to build pressure again.

ethicalpaul

EBEBRATT-Ed said:

actually the vacuum is good the rads will keep heating as the steam cools giving you more heat.

But the vacuum needs to go before the burner fires again as it will hold condensate in the system.

Usually the vents will take care of this.

Tunstall has good steam vacuum breakers, you can also use a swing check valve (a good one with the gate on a 45 deg angle) not a up and down gate. They are called Y pattern check valve

I don't want to hijack things too much, but I do disagree a bit with @EBEBRATT-Ed (who I respect so much) on the topic of vacuum holding back condensate in a 1 pipe system.

I can't picture where it would be held back. The vacuum is generally equal throughout every pipe and radiator so what would prevent the condensate from running back home?

It's not like a bottle turned upside down where the water itself prevents or hinders air from getting in.

The condensate is just water flowing along the bottom of some pipes in less than normal atmospheric pressure--what would hold it back? Maybe I'm missing something that would hold it back but I honestly can't think of it. Sorry for the interruption

AdmiralYoda

@ethicalpaul Its on my to-do list. My system heats well but is still somewhat imbalanced. No header, each main connects directly to its own riser. One main does not have a vent because there is no place to put one and that main is piped like it was a high school project.

It is getting repiped this year.

PMJ

ethicalpaul said:

sorry not you PMJ, I meant Admiral Yoda

I should have noticed. Anyway, his timer is great, but all should consider the point of avoiding pressure in the first place.

Note: I do get that pros will have a tough time with this because it will be hard to get owners to pay for all the time required to balance unbalanced systems. The live in boiler man(like me) has a huge huge advantage. I do get this. Owners likely won't get why their systems can't just be fixed all in the boiler room and why they have to let the boilerman run all over the house in every room multiple times. I got to sample all the different conditions anywhere anytime. If the meter had been running on all my time it would be a big number. So I expect all that often all that can be done is raise the pressure some to push steam somewhere.

I hope we can separate the two subjects and still discuss the theory while acknowledging the obvious real world constraints on the pros. Life is so much better with no measurable pressure and is not hard to do even with big boilers. Systems have to be balanced though.

EBEBRATT-Ed

My ex mother in law was a saint. He daughter (my ex) not so much. When I got home from work my wife would hand me a balony sadwich.

When momma was visiting (she loved to cook) I would walk in the door and ask her "how many burners tonight mom" she would say "only three but the oven is on too" I miss her but my waist line didn't.

What's that to do with steam? She would boil water for spaghetti and when it was boiling throw the spaghetti in shut the gas off and put a cover on the pot to let it cook for 10 min. Worked like a charm.

I would asks her "why are you doing that mom"? "Ed I don't want to make a gas bill for you"

So I understand @AdmiralYoda's timer and @PMJ controls

She was letting the hot water do the work.

A steam boiler especially and oversized one that is shut of with the boiler and pipes at full steam will continue to "cook" for a while.

Thai may not work on all systems or all boilers but I could see this happening in a residential job with an oversized boiler

A little like the Heat Timer and Tekmar controls that run the boiler until "steam established"...hot pipes and hot boiler then run it for a period of time based on OD air not the same as not letting the rads get full as @PMJ but some similaraties.

Most contractors won't take the time or spend the customers money designing a custom control system they want something plug and play but I can see the usefullnes

PMJ

EBEBRATT-Ed said:

My ex mother in law was a saint. He daughter (my ex) not so much. When I got home from work my wife would hand me a balony sadwich.

When momma was visiting (she loved to cook) I would walk in the door and ask her "how many burners tonight mom" she would say "only three but the oven is on too" I miss her but my waist line didn't.

What's that to do with steam? She would boil water for spaghetti and when it was boiling throw the spaghetti in shut the gas off and put a cover on the pot to let it cook for 10 min. Worked like a charm.

I would asks her "why are you doing that mom"? "Ed I don't want to make a gas bill for you"

So I understand @AdmiralYoda's timer and @PMJ controls

She was letting the hot water do the work.

A steam boiler especially and oversized one that is shut of with the boiler and pipes at full steam will continue to "cook" for a while.

Thai may not work on all systems or all boilers but I could see this happening in a residential job with an oversized boiler

A little like the Heat Timer and Tekmar controls that run the boiler until "steam established"...hot pipes and hot boiler then run it for a period of time based on OD air not the same as not letting the rads get full as @PMJ but some similaraties.

Most contractors won't take the time or spend the customers money designing a custom control system they want something plug and play but I can see the usefullnes

I do get the very real need for something plug and play (and probably industry approved in some way).

The idea is so simple and so effective though I do find it astonishing something hasn't made it to that point in all these years.

OleksiiC

@AdmiralYoda I have similar issue with one radiator vent going to the moon after call for heat ends. And what i found so far is that out of four gortons #1 only one (the farthest from main) opens and is not capable to let all the air in. So the solution i'm going to apply - moving vent manifold higher. I also considered adding vacuum breaker, but it's going to be another failure point (taking into account the "quality" of plumbing supply sold nowadays)

The schema of vent manifold i have (except of that it's less than 6 inches from steam main):

cross_skier

Looks good!