best vacum braker for steam system

charlie_22

What is the best type vacum breaker for a steam system any help is greatly appreciated

nicholas bonham-carter

vacuum breaker

i use 3/4 check valves on the ends of my vent antlers. they are mounted horizontally and up right.

i think the larger diameter check is more likely to open the moment the vacuum develops. a bit of exercise for the flapper may be necessary before installation as some of them can stick a bit. 1in. checks might even be more responsive.--nbc

Jamie Hall

Do you mean

a device to keep the returns and mains from going into a vacuum when they cool?  Because if so, almost any vent (with a couple of exceptions, like the Hoffman 76) will do that.  Or do you mean a vacuum breaker, such as might be found on a water supply line, or at the top of an inverted loop?  Very different animal.

charlie_22

vacum braker

when my system shuts down I get a whistling from the air vents. I just replaced my whole steam main in june and I added spots where I can add vacum breakers one by the boiler and one almost at the end of the main about 3 feet from the main vents I also added two gorton #1 main vents.I am presently using watts#N36-M1 vacum relief valves but they do not seem to relive the vacum I was just wondering if there was a different type of valve that you guys used that has maybe a lighter spring or something or shoud I just install another main vent in those locations thanks alot Charlie

FJL

Air Suction

I get suction whenever the system turns off after satisfying the t-stat or when it cycles off due to pressure.  Should I be installing something somewhere to prevent this?

Jamie Hall

Suction and vacuum

When the burner shuts off, steam is no longer being made and the steam will condense.  Any type of vent -- with a few exceptions -- will allow air back in.  For Charlie, though, it is possible (likely, in fact) that additional vents would help the whistling -- and might help the overall heating, too.  For FJL, the suction you describe is normal.  Back in the bad old days of coal, some systems were designed to run on at a vacuum when the fire died down.  Modern systems are do not need to..  If you are really getting a vacuum (suction) this isn't bad -- but as I note above, you probably have inadequate venting, which causes other problems as well.

FJL

Inadequate Venting

If you can, what is the relationship between inadequate venting and a sucking sound in the vents when the boiler turns off.

Jamie Hall

As the steam

condenses, the air rushes back in.  The fewer or smaller the vents, the faster the air has to move to get through the vents -- and the louder the sound will be.

Big-Al_2

Tried a Couple

No matter how many vents you have, without a vacuum relief valve, the first vent to open up will generally relieve the vacuum all by itself.  My experience is that the first one to open will vary from cycle to cycle, and some radiator vents absolutely screech under vacuum.



The commercial vacuum relief valves out there seem to be made specifically to prevent a tank from collapsing under high vacuum, rather than to quickly allow air back into a steam system.  I tried a Watts N36 vacuum relief valve on a main vent antler.  It worked OK on vacuum, but didn't seal reliably with steam, and would sometimes hiss and dribble.  It is supposed to be on a pigtail to protect it from live steam. I didn't have a pigtail handy, so I made an s-trap for it with pipe fittings to try to accomplish the same thing.  When it would relieve, it would make a gigantic slurping noise that could be heard all over the house.  That setup lasted about two days before it was trashed.



I also tried a Hoffman 62 (aka Bell & Gosset 26) vacuum relief valve.  Its stiff spring doesn't allow for a very light setting, and even wide open, it's very restrictive so the radiator vents still suck in air.  I enlarged the flow passages on one, and set the spring as lightly as it would go, but it didn't seem to help the sucking noise upstairs.  



I also tried adding multiple Hoffman 75 main vents to the system.  That does seem to vent the main more quickly as steam builds. However, under vacuum, most of the time, a radiator vent opens before one of the main vents anyway.



NBC's idea of using standard horizontal swing bronze check valves does sound interesting.  I've been hesitant to try a hard-seated valve like that, because I suspect that they might not always close tightly, but maybe I'm wrong..



In my case, I identified a radiator vent that seemed to seldom be the first to open and moved that one into the main bedroom.  The couple of vents that seemed to be opening sooner than others are now located further away.  At least the super-sized sucking sound doesn't wake me up at night . . . as often.



btw:  Hoffman 40 and Maid-O-Mist #5 vents seem very quiet under vacuum, possibly because they have such a small orifice to begin with.