Air Vents v. Vacuum Breakers

NewlyPuzzled

What is the difference between an air vent and a vacuum breaker?

Where do each of them go?



Thank you very much with your help with this question!

Jamie Hall

They do very different things

But are often combined in steam heating systems...



An air vent is a device which allows air to be released; in steam heating, we are usually thinking about releasing air from a main or from a radiator.  They are designed to close under certain conditions; again, in steam heating, they should close against water or steam.  Automatic air vents may also used in some hydronic applications, and in some water supply applications (but almost never in normal plumbing).



A vacuum breaker, on the other hand, is designed to open when the pressure inside the pipe (or radiator, or what have you) is lower than the pressure outside, thus preventing a vacuum from forming.  Devices which are specifically vacuum breakers are occasonaly found in steam heating systems, but they are relatively common in plumbing applications.



Most steam heating air vents that you see mentioned on the Wall are also vacuum breakers.  You will occasionaly run into an air vent which is NOT a vacuum breaker on some vapour systems -- but they are rare.

NewlyPuzzled

Follow-up

Okay, thanks!



Well, here is my problem. I am the assistant manager for a 14 unit apartment building. We are having lots of trouble getting our steam heating system functioning properly. Currently, we are having trouble with two of the units on the 1st floor. The radiators in these units are filling-up with water and spraying water out of the air vents on the radiators despite having new air vents.



If there are no main line air vents, could this cause this to be happening?



I am thinking that perhaps a vacuum is being created in the system, preventing the water from draining back to the boiler.



Do the main vents work as a vacuum breaker too, then? Or, should we consider installing an actual vacuum breaker as well.



Thanks to anyone that can help with this lingering problem!!!

JStar

Steam

Is this two pipe steam? What pressure is the boiler running at?

Paul48

When

was the last time the system was serviced by a steam pro? Generally, when things get out of whack in a fairly large system, it is cheaper and faster to bring in a steam pro to take care of immediate problems, and ,perhaps, provide a list of things that can be done to improve the system. Running the system as it is, is wasting money. If it was the spring and you had time, I'd say proceed, but it's cold outside.

NewlyPuzzled

Thanks

Thanks Paul48. Yeah, we have had several professional companies look at the system. It does not appear we have *any* main line vents. I have tried to stress the importance of these (based on the research I have done and "We Got Steam Heat", but nobody is listening to me. I am trying to get more information for the owner so maybe I can get through to him.

NewlyPuzzled

System Specs

- one pipe steam

- low pressure (2-3 psi)



Thanks!

Paul48

Puzzled

Where are you located? You have not had a steam pro look at the system, if they don't recognize the need for main venting.

NewlyPuzzled

Paul48

lol....tell me about it! The building in located in Kansas City, MO. My understanding is main venting is absolutely essential. But, like I said, the owner does not think I know what I am talking about and only wants to implement what the "professional" company recommends. At this point, I am just trying to figure-out if there are no main vents, could this cause a backup of water in individual radiators? Maybe if I can answer this question definitively, they will give my suggestions a try!! :-/

BobC

Pictures?

Single pipe steam systems usually have vents on the mains, does the system have condensate pumps? Also what kind of radiator vents are you using?



If you could post some pictures of the boiler and the piping around it, the pro's on this sight might spot something that would help. Also where are you, there might be a pro near you that could take a look and give you some advise, you would be hard pressed to find more knowledgeable people in the industry.



Bob

Paul48

Yes and No

The lack of main vents is forcing you to run the pressure higher than it should be run at.The higher pressure is causing the vents to fail. The system has to be evaluated as a whole. We have seen the very predicament you are in before.We had an intelligent condo owner that was trying to straighten out their steam system, but the "Board" would only listen to an idiot that claimed to know what he was doing. Do yourself a favor....run! There's an old saying,"Never wise up an idiot, or he'll leave you behind".You're not the idiot.

NewlyPuzzled

Paul48

Paul - You have no idea what your comments and advice mean to me! I feel like I have been beating my head up against a brick wall trying to get the owners to listen to me. I am very close to walking away from the whole deal. It has been *very* frustrating. They have already spent lots of money trying to resolve the issues without starting with the most obvious one. At first, I just thought that maybe the main vents were clogged. I finally got the service tech to walk through and show me where the main vents were. I was astonished to not even find one main vent. They have all been removed!



According to my research and what I have read, there is no way to have a properly functioning system without these main vents. Absurd!!! I was really starting to doubt myself though. Thank you for helping to reinforce that I am not on the wrong track.



Appreciatively Yours,



Brian

nicholas bonham-carter

What a predicament !

You are now caught between the tennants and the owners.

The main vents, and radiator vents will allow air back in, after the burner has cut off, and the condensing steam forms a vacuum.

What make of boiler is installed, and how old? If it were a Peerless (for instance), they have very superior tech support, and knowledgeable local reps who might be able to explain to the heating company the importance of main vents. Certainly, their installation advice is first rate.

Since the owners have no technical knowledge, the heating company will have to become more steam savvy. Invite them to ask here.

I suspect the pressure is much higher than it should be, and that gas is being wasted in quantitiy.

Keep us informed what progress you make!--NBC

NewlyPuzzled

BobC

The system does have a condensate pump on the Southwest corner that pumps condensate to the main holding tank behind the boiler (Northeast corner of building). The main holding tank also has a pump to pump the water into the boiler. I have not been able to locate *any* main line vents.



Currently, some have adjustable air vents, but most of the radiators just have the traditional "bullet-style" air vents on them.



I think we have to get main line vents installed. Without those, I don't think anything else is going to help. I'm in Kansas City, MO.



Thanks for all your help!!

NewlyPuzzled

NBC

It has been very frustrating trying to get the owners to listen to me and the mechanical company to validate what I am saying...even though I have spent countless hours researching, reading "We Got Steam Heat" (I've referenced it so many times the pages are falling out), and providing them tons of information to support what I am saying.



I think without main vents, there is not enough air getting out of the system and not quickly enough. I think the system is also not getting enough air back in when the burner cuts out.



The boiler is a Weil-McClain 480,000 Btu and was replaced in 1982, I think.



The cut-in is set at 0.5 psi and the differential is set at 1. The thermostat had to be moved because some of the apartments were not getting enough heat. This of course, makes the boiler run longer to get the temp up in those apartments. I am wondering if that creates too much pressure and the vents are failing because of that.



Thanks for your help!!!

nicholas bonham-carter

KC venting problems

The pressuretrol seems set as well as it possibly could be, as far as pressure goes. Something which can happen to them is that the pigtail underneath them can become blocked with debris, and then the pressure never gets through . This isolates the pressuretrol, and allows the pressure to run wild. Is the pressure gauge working? Can you hear excessive noise from the radiator vents at the start of the burn cycle? Is there any water-hammer?

Is this your first winter with the system? Did the system ever work right? Does it use much makeup water?

Can you make a simple diagram of the piping layout, showing the dry returns, where the vents would be placed?--NBC

NewlyPuzzled

NBC

Thanks for getting back to me.



The pressure gauge was replaced as part of the "overhaul" performed by the mechanical company. The old one was too big. It was working when they installed it. It never really registers though because usually the thermostat is satisfied before there is any movement on the gauge.



YES!...hahaha...the air venting from the air vents on the radiators is sometimes very loud (hissing) as well as the water hammer that sometimes occurs.



This is my second season with the system. Last year was horrible....sometimes it was freezing in the apt., sometimes it was 84 degrees...lots of sludge in the radiators...water spitting from valves....water hammer...etc.



I only lived in the building last year and am in the process of taking over management. I insisted the (soon to be former) manager call-in a professional. They overhauled the system, but we are still having some issues.



I am not sure how much make-up water it is using (auto-feeder)??.



I can probably take some pictures if that would help?!?!?

Jamie Hall

Problems, problems...

Something like this, it's really hard to know where to begin!



Main vents: you do need them, badly!  Probably good big ones, or even two or three, on the mains.  If you can get the diameter and length of those mains, we can help size them.  Is this a multi-story building?  If so, vents at the top of the risers might also help.



Pressure: 3 psi is too much.  You should be running a maximum cutout pressure of 2 psi.  Many radiator vents won't reopen unless the pressure drops below 2 psi, and this can cause trouble (usually no heat, or very poor heat).



Assuming the pressure is not too high, modern radiator and main vents all open on a vacuum; you shouldn't need a vacuum breaker anywhere on the system.



You mention that there might be a water hammer problem.  Can you say when in the cycle this occurs?  The causes are many and varied, but it does help to know when it occurs.



The radiators shouldn't fill with water, obviously!  But there are, again, a variety of reasons why they might.  Tackle the above stuff first, and then see how far you've gotten.  You can do all the above stuff even though it's cold outside!



And good luck...

Paul48

Sanity

I suggest you show the owners diagrams of a proper one-pipe steam system. Highlight the missing main vents, and explain that this is costing them un-necessary money.If they still won't listen...drop it, and dumb down. Boy, I hate to say that! The design principals are the same from the smallest to the largest systems, the only difference is the scale. http://www.gogeisel.com/geiselonline/support/Hoffman/Steam_Vents/Basic_Steam_Heating_Systems_1_2_Pipe.pdf

RJ_4

rad. valves

I agree with all the pro's that have got back to you.    One other thing to check is the radiator valves.    In the past I have found rad. valves with cracked and deteriorated disk material ( disk is what closes against the valve seat )  what was happening was the valve was allowing steam into the radiator but not allowing condensate to drain back.   to check, shut off steam supply , disconnect the union on the valve, move the radiator and inspect the valve disc and seat.  the problem can also occur if the tenants are trying to use the valves as a  proportional control,  rad. valves must remain all the way open on 1 pipe systems. the tenants must be aware if they shut off a radiator. when the radiator is turned back on ( valve opened again )  there will be air and water in the radiator, you can expect banging and some spirting of air vent until water is allowed to drain back to system.

Jamie Hall

Good call, RJ

I didn't even think of that -- and that would surely get you water in the radiators and spitting and banging on those radiators and all kiinds of nuisances.



On one pipe steam, the radiator valves must, repeat must, always be full open.  If the radiator is heating too fast, put in a smaller vent.  If you want to turn the radiator off, turn the vent upside down.  But do not try to modulate or turn off the radiator with the valve.

Paul48

Brian(NewlyPuzzled)

Tell the owners that any changes you propose would be backed up by written history, not guesswork. The changes will save them money. You will have to drag them along.Post some pictures of the near-boiler piping.Stand back so we can get an idea if that is done correctly(to manufacturers specs).

NewlyPuzzled

Jamie

Thanks for the additional information - it is very helpful! Yeah, it has been frustrating!!



So far, I have been unable to convince the owners that the need for main line vents is *essential*. If they are not willing to start there, I do not think there is any point in trying anything else (at least before solving that problem first).



The building is 3 stories with a basement. So, if the cut-in is set at 0.5 psi and the differential (dial inside the pressure control box) is set at 1 - does that mean the cutout is 1.5 psi???



Thanks for clarifying on not needing an additional vacuum breaker.



There is definitely water hammer that starts at the beginning of most every cycle. It is worse when the boiler has been off for longer periods of time (inconsistent/warmer outside temps.)



I will continue to try and get through to the owners. Thanks again for all your help!

NewlyPuzzled

RJ

Thank you for the additional info. One of the things I initially suggested is the complete inspection of each individual radiator. But, that was not done. If I can somehow manage to convince the owners this still needs to be done, I will make sure to include that in the list of things to check - thanks!



I have had a lot of trouble convincing tenants not to shut off their supply valves. Unfortunately, the (soon to be) former manager (and former owner of the building), has been doing things and telling tenants wrong for many years. It has been extremely hard to get through to them (tenants and manager) the way they have always done things is wrong. I even suggested some locking mechanisms be installed on the radiator supply valves, lol.

NewlyPuzzled

Jamie

Thanks for the follow-up!

NewlyPuzzled

Paul48

Thanks for the continued help. I will certainly do everything I can to resolve the issues!



I will try to get pics posted soon!

David Nadle

Vacuum is not the issue

You need main vents of course but I don't think adding them is going to fix your problem. If the first floor radiators are filling with water and it's spitting out the vents then that is most likely because the radiator valves are closed or the returns are blocked.



From my experience as a tenant in NYC I believe the standard way to deal with recalcitrant tenants is to fully open the valve and then steal the knob...



Based on what you wrote I think you have to troubleshoot and fix the two problem radiators first and then bring up the subject of main vents, because I fear that if you add main vents and the radiators still spit water you will have lost credibility.

BobC

Fix a problem and garner some credibility

You mentioned that some of the radiator valves were the bullet shaped variety, those are probably Hoffman 40's and they are usually very good for fixing balance issues on systems like this. What kind of vents are being used on the radiators that are spraying water? I hope they are not Heat Timer Varivalves, they are famous for acting like fountains in some settings.



One way to combat people turning radiator valves half way off would be to disable the valve's closing ability and then put a TRV on those radiators that seem to be putting out to much heat. Then they can dial the temperature they want without causing ancillary problems. The difficult part will be doing only the radiators that need it and not have to add a TRV to others just because they want one too.



That is where the art of diplomacy comes in. And perhaps if you can pull this off you will garner enough credibility so they will look more favorably on adding main vents.



Bob

NewlyPuzzled

David and BobC

Thanks for the additional information guys! The more information I have, the better I will be able to work towards a solution.

Paul48

TRVs

TRVs are great, and can make for a very comfortable system. They are also not cheap, and we shouldn't recommend them without knowing what control strategy is being used for the boiler. They require a reset control on the boiler, and the system must go to zero pressure for them to work. I'm not saying you wouldn't benefit from them, I just think they may be down the road a bit.If you start by giving us the length and size of the mains, someone will tell you what size vents are needed. If the vents have been removed, you can put them back, it's not hard. You will also be able to tell the owners how much the new vents will cost.

nicholas bonham-carter

When to use TRV'S

TRV'S are a sort of beneficial bandaid, to be used only after all balancing issues have been addressed. For the cost of one TRV, you can put in 3 gorton#2's. In a system with no main vents, this is the first priority.

When this system was first installed, there were no TRV's, and yet the system was even and economical. Later changes to oil, and then gas have introduced new constraints on the system, which require even more main venting than before. My list by priority would be:

1:replace the main vents, to provide maximum venting.

2.install an accurate low-pressure gauge for diagnostics.

3.examine the control system for problems (going back to a thermostat in place of anything more complicated and iffy, like a heat timer.

4.Make sure there is no setback and no valves turned off.--NBC

Paul48

Brian

I posted that link to Basic Steam Systems. I suggest you start by drawing simple diagrams like the ones on that site. You need to find out everything that's wrong with the system.It doesn't all have to be done at once.If you're drawing the boiler straight on, and a main goes away from you for 40 ft, you don't have to try to draw that. It's not important. The over-all length of the main, its size, and what it does at its end as it changes to return is all thats important.

David Nadle

Don't blame the vents

I disagree that TRVs are a "band-aid." Sometimes radiators are well balanced but the room is still too warm. Sometimes you slow the radiator down but you're cold in fall and spring. In my opinion TRVs have little downside except the cost, and the cost is reasonable. If you told me 20 years ago that for $100 I could prevent my apartment from becoming an oven and I could stop opening windows in February, I would have gladly paid.



But I do agree that they should be installed only after basic system deficiencies have been addressed. Pressures should be below 2 psi. Radiators shouldn't be hissing or spitting water. The mains should be well vented. There should be no hammer. TRVs are not going to fix a broken system, but they will do wonders for an oversized radiator.

NewlyPuzzled

***ALL***

Thanks guys for all the help and advice. The *one* thing that has been consistent in ALL my research and the advice I have gotten on this site is the absolute need for vents on the main (main line air vents). This seems like such an easy and affordable option to try. I just wish I could get the owners to realize this is the best place to start. Nobody has said that venting the main is an *option*. Even if that does not fix the problem, it is still necessary for the system to operate as it should.



If anyone disagrees, please let me know!



Thanks,



Brian

NewlyPuzzled

HELP!!!

Paul48 - Thank you so much for posting the link to the 'Hoffman Specialty Schematic'. But, now I am really confused (my fault, not yours).



Ok, we definitely have a one pipe system. But, then there are 6 different types of "applications" for that system listed in the schematic (dry return, down-feed, mechanical return, wet return, up-feed and a counter-flow). Is it only possible to have one of these applications...or, are these all the different parts of the overall one pipe system???



I guess we probably have the "mechanical return" application because we have a condensate pump. I am not sure what other parts of the 6 applications we have though. And, I see no main line air vents on the "schematic for the mechanical return" application.



Could you please help clarify for me. If anyone else can set me straight, I would greatly appreciate that too!



Thanks,



Brian

nicholas bonham-carter

Same thing, different terminology

David and I are in agreement , just different terminology. Perhaps I should have called TRV's a coping device for oversized radiation, but not to be used to mask system imbalance.

Here is the peerless boiler info which may be easier to follow.--NBC



http://www.peerlessboilers.com/DesktopModules/Bring2mind/DMX/Download.aspx?EntryId=140&PortalId=0&DownloadMethod=attachment

Paul48

nbc

That's much easier to follow. Brian...It may say this but I'll say it for clarity. Parallel and counterflow refer to the paths of  steam vs condensate. In Parallel the steam and condensate flow in the same direction. In Counterflow they flow in opposite directions.Notice the pitch of the mains in the diagrams.The condensate will go whichever way the main is pitched. The steam will only travel from high pressure to low.In a system with no venting there is no pressure differential. Therefore, the steam does not flow and just builds pressure.

http://www.masterplumbers.com/plumbviews/2002/BasicSteam.asp