How Do I Eliminate Radiator Vent Hiss

Big-Al_2

I'm going to ask this for the millionth time here.  How do I eliminate radiator vent hiss.

Dan says that they should be silent.  Mine aren't loud, but they are audible as the system heats up.



1) Better main venting?  I have multiple Hoffman 75 vents on an antler at the end of the main.  The radiator vents are silent until all of the main vents close . . . then they start to quietly hiss until they close.  I can't see how adding more or bigger main vents is going to make a difference, because they will all be closed before the radiators start venting.



2) A lower pressure setting? C'mon, the radiator vents start making venting noises as soon as the main vents close, long before the radiators are even hot all the way across or the boiler gauge gets off of zero.   By the time the boiler reaches .5 PSI, all the radiators are done venting and everything is quiet. 



3) Different brands or sizes?  I've tried Hoffman 40's, Variable ones from Watts, various sizes from Maid  O Mist and Gorton, and a couple of Varivalves.  Some are quieter than others.  Some hiss.  Some make sort of a heavy breathing "ahhhhhhh" sound. Some gurgle.  Some make a  pinging sound when they close and some whistle loud enough to wake me up when the boiler shuts off and the system goes into vacuum.



I'm more and more convinced that the statement that a properly configured single pipe steam system should be silent is somebody's idea of a cruel joke to make people like me go nuts trying to make things work that way.



Other suggestions?

kcopp

Well lets do this...

Go back to the beginning... What do you have? Boiler make , model, size. Main size, how many rads? System Age. Insulation... Pictures? Then see what we can do. Is it all rads or just a couple?

David Nadle

Wet steam

Based on what you wrote I think you are making wet steam. That could be a bad installation (post pictures of the near boiler piping) but more likely you have oil or other contaminants in the water. Skimming should help but you may have to do it several times. Many pros here eschew chemical additives but I have to say that one dose of Hercules boiler cleaner helped me solve a similar hissing problem. 

The Steam Whisperer (Formerly Boilerpro)

Is the boiler too big?

If it is pushing steam to hard, the vents will hiss.  I agree, it is probably not a need for more main vents, since it is quiet until they close.  I'd check your radiation capacity versus the boiler capacity.  I like it to take about 1 hour for the system to completely come up to temp, if it all.

JStar

Also.

As mentioned before...how is the near boiler piping arranged? You could be pushing the steam out of the boiler too fast, if you have a single or undersized supply tapping on the boiler. Or an undersized header. 

nicholas bonham-carter

vacuum vents??

just check your hoffmans, and make sure they are not the vacuum model [76?]. besides, being slightly more restrictive on the pressure part of the cycle, they are not able to relieve the vacuum, obviously!], although the vacuum feature can be removed. Even hoffman 75's are only a fraction of the capacity of the gorton #2, so i would try those, alongside the hoffmans.

 if you are slightly overfired, or if your pressure is over a few ounces, then you definitely could be over-working the poor radiator vents. what is your pressure anyway?--nbc