Hissing air valves after shutdown and balance problem

Unknown

Hi Jeff-
I'm a bit confused with your phrase: "but as soon as the burner kicked in the vents were hissing as the air rushed back in to displace the steam." Since the system starts to build steam pressure when the burner "kicks in" it would seem to me that it is air escaping rather than being pulled back in.

Since increasing the pitch of the radiators helped, you might consider increasing it a bit more. I thought I had lots of pitch in one of my radiators till I discovered that the house had settled and the whole floor was pitched the wrong way. Big old radiators sometimes sag in the middle so need a little extra pitch.

You have a lot of venting on your radiators. (A Gorton "D" is equal to a Gorton #1) What I'm wondering is maybe you have too much. While not a usual occurrence, it is possible to over vent radiators. Gerry Gill discusses this on the last page of his book, "Balancing Steam Systems - Using A Venting Capacity Chart" by Gerry Gill & Steve Pajek. It's available on this site as an "e-book".

http://www.heatinghelp.com/shopcart/product.cfm?category=2-138

If you don't already have it, it's well worth getting.

I think I'd test out the venting on the radiators by removing the vent and see if the radiator heats up without any vent. (put a nipple and a ball valve temporarily on the vent hole so you can shut it if it starts to spit water)

You might also want to check the vents on the non operational radiators to see that that haven't picked up some dirt and are partially clogged. One of the problems with high capacity vents is the high volume/capacity venting flow tends to pickup loose dirt/rust.

A possible "fix" if you think you have over venting might be to put TRVs on the hottest radiators. Make sure the ones you use have a vacuum breaker on them. (See an earlier post on this thread for links)

Nice diagram by the way - Well thought out. Which are the "problem " radiators?

V8toilet

Hissing air valves after shutdown

I have a steam system that has been very difficult to balance. The upstairs floor of this home gets too hot even if I completely shut off all the upstairs radiators. This is because there is no insulation in the second floor framing and the staircase is an open staircase allowing the hot air from the first floor to just rise upstairs.

The problem is that the upstairs radiator valves hiss after the system shuts down and the remaining steam in the system collapses and the air tries to rush back in. The air valves I have installed on the upstairs radiators are very slow venting Matco Norca valves (about comparable to a Maid-O-Mist #4). This a very small 1 pipe steam system (~220 sq ft). The mains are all vented very well and the system works fine. The system also heats very quickly and the makes no noise during the heating cycle. Is there a vacuum breaker that I can install on those affected radiators that will remedy this problem. If a install quicker venting air valves the upstairs radiators heat more quickly and really overheat the upstairs combined with the rising hot air from below. The downstairs radiators do not hiss at all. This is very frustrating!

Unknown

Both these TRVs come with vacuum breakers. Not sure if that's quite what you are looking for.

Macon

http://www.maconcontrols.com/pdfs/OPSK1204.pdf

Danfoss

http://na.heating.danfoss.com/PCMPDF/RA2000 1PS-DS.pdf

nicholas bonham-carter

hissing vents

maybe you should still increase the capacity of your main venting, to relieve the vacuum.

another solution might be to install a check valve on the downstream side of the main vent itself. that way, at the end of a burn, the check valve can open to relieve the vacuum, when the steam collapses.

the hissing radiator vents would indicate a need for more venting capacity. ideally they should only be handling the air/vacuum on the riser alone.--nbc

Jeff_130

Please expand on this...

NBC:

I have 3 old ornate column type rads that have been extremely slow to heat up beyond half way, even when their supply valves & the other tube rads are schorching (and with it being 5-15 degrees out). I increased the venting capacity but that seemed to do little. After some more reading I decided to increase the pitch which got them hot all the way across for the first time last night but as soon as the burner kicked in the vents were hissing as the air rushed back in to displace the steam. My mains are vented with Gorton #1s (2 ea.) - which is significantly more venting capacity than I originally calculated but wanted to ensure adequate main venting and these rads all have either #C or #Ds.

Shouldn't the rad vents stay closed and hold the steam? Any thoughts/advice are greatly appreciated. I've attached my calcs & a diagram of the system.

Thanks.

Jeff

nicholas bonham-carter

noisy vents

sometimes it helps, not only to raise up the end of the radiator, but also BOTH ends of the radiator.naturally the slight downward pitch has to be maintained. in the "2-dollar" solution mentioned on another post here should be expanded to the 5 dollar solution:4 quarters under each leg closest to the valve, and 6 under each at the far end.

the job of the vents is to remove air as the steam is rising, and to allow it back in when the burner stops and the steam condenses en masse.if the radiator vents are making much noise at all, then i would suspect them to be under sized [even though they are handling the air evacuation alright]. perhaps you could make sure of the following in this:

1.system pressure to be as low as possible-under 16 ounces is best.

2.increase the main vents a bit [maybe # 2's]

3.make sure the biggest radiator vents you have are at the top of any 3rd floor risers with lower capacity vents on the ground floor.

4.5 dollar solution mentioned above.

--nbc

Jeff_130

Rod:

I didn't hear any hissing when the burner was running (and this rad is far enough away from the boiler that I would have). It was after it went off that the hissing began so I am assuming that with no further steam pressure buildup from the boiler the hiss was air returning.

As far as pitch is concerned, I will put a level on the problem rads this weekend and make sure that I've got adequate pitch.

I already picked up the venting e-book and that is what I used as the basis for my calculations. When the air did not vent I increased the vent size on the problem rads. I didn't realize that the #D & #1 were equal - cool. With the newly pitched & heating rads I will adjust the vents.

All the vents are brand new and besides the problem rads did not heat any better when I removed the vents entirely.

The problem rads are Second Floor North & South as well as Foyer South (in red on the diagram). I shut the 3rd floor West rad off to make sure that all the steam wasn't getting sucked that was (as discussedin in "Balancing Steam Systems").

I'm thinking that instead of TRVs I will reduce the size of the vents on the hottest rads as a means of slowing down the venting and having the steam follow the path of least resistance to some of the other rads to complete balancing.

Your thoughts? Thanks.

Jeff

nicholas bonham-carter

slow steam?

don't forget that the effect of putting on larger or smaller vents on the radiators, is to increase or decrease the SPEED OF ARRIVAL of the steam to the radiators. once the steam has arrived, the vent closes, and has no more effect on it, until burner shutdown. therefore if the burner runs for 15 minutes, you don't want the riser to take 5 minutes to get the air out.

the main vents should be doing most of the work, with the radiator vents handling the riser portion.--nbc

Unknown

Hi Jeff-
Sounds as though you are on the right track. Probably the first thing to do is make sure the "problem" radiators are functioning properly. If you're happy with the slope, about the only other item to check would be the radiator supply valve. If you suspect that these might be non or partially functioning you may want to check them out further. With the vent removed you should be getting good flow. Maybe if you shut down the other radiators temporarily, that should increase flow and give you an idea whether the flow going into the problem radiators is obstructed or not.

I was wondering if you had the Gerry's venting book already. Take a look at the last page "Update – Winter 2005, 2006 - Can you vent too fast? ". When I was reading your post it just struck me that your situation was very similar to the one Gerry described especially when I read about the cold weather (increased condensate)

Reducing the vent size on the hottest radiators should help.
I was thinking about TRVs with the idea those rooms would heat first and then steam would be directed to the problem radiators. I guess it sort of dependent on what you want your heating priorities to be area wise. I'd just keep experimenting until you are happy with the system.

You might want to pickup a couple of HeatTimer Varivalve

http://www.heat-timer.com/?page=varivalve

http://www.heat-timer.com/literature/VariV056082C.pdf

The angled model is part # 925005-00 .
These have adjustable venting and according to Gerry & Steve's chart, the minimum setting is between the capacity of a Gorton #5 and a #6 and the maximum is almost twice a Gorton # D . I found being able to adjust the vents was really helpful when I was working out my balancing.

It sounds as though my house is similar to yours - an old 3 story with the upper floor shut down. This last year I insulated the boiler steam piping and mains and it has made a BIG difference. Most of the original asbestos insulation had been removed and hadn't been replaced.

V8toilet

Can we get back to the original question here!

The only radiator vents that hiss are the upstairs radiators, not the downstairs radiators. The mains are vented with about 2.1 cfm each or about the capacity of a Gorton #2 main vent. The longest main is a 2" main that is about 35 ft long. This is a small system with about 220 sq ft of radiation. I have very slow venting valves on the upstairs radiators because even with those radiators shut down completely the upstairs gets too hot. The upstairs gets too hot because the downstairs heat rises due to no insulation in the intermediate floor and an open staircase that allows the heat in the downstairs to just rise. Because this system is sized to the heat load of the home the radiators often completely fill from top to bottom with steam. When the burner shuts down the completely filled system of steam collapses and creates a vacuum that causes the air valves inside those upstairs radiators to hiss.

Is there a vacuum breaker that I can install to help eliminate the hissing upon system shutdown. I know about the TRV's but I was hoping that I could just get the vacuum breaker due to cost.

Unknown

I guess what you're asking for is a high volume vacuum breaker to help the vent so that it doesn't hiss forever. Other than what units that come with the TRVs I never seen one for steam heating that is "independent".

I haven't used this for steam but it might work for you. I set up a liquid system a few years ago and we used small check valves as vacuum breakers. They worked pretty well. Price was reasonable too. We got the valves from the Mc Master Carr.

http://www.mcmaster.com/

This will take you to their catalog page.
Try "check valve" in their search and then look for "spring loaded check valves"

Pay particular attention to "cracking pressure" rating (though I guess with atmosphere vs vacuum, you have a 15 PSI advantage) This is how much pressure is need to open against the spring. Also look at the temp rating as most have rubber seat seals

You might also look in the catalog`for brass pipe tees or what ever other hardware you need to hook up the valves. They have a good selection of different types and finishes.

- Rod

nicholas bonham-carter

too much of a good thing?

rod, i reread that last page of the e-booklet, and i still have trouble with the description of that particular over-venting problem. surely there must have been some restriction on the non-functioning rad. the vents cannot control the steam once it is in the radiator, only the speed of its arrival. i can see the problem of allowing too much speed into a cold rad and subsequent condensate over production. either the pressure was way down or their could have been a subsidence on one side of the wall placing more restriction on that rad.maybe i will start a new thread-what is your opinion?--nbc

Unknown

Hi Nicolas- I wondered about that too. I'd sure like to get a look at the piping. One supply line with two branches, what are the possibilities?

1. You could have a tee feeding both branches. This isn't probably likely with the aversion that steam men have to bullheaded tees. Also the returning condensate steams would collide which would cause problems.

2. You could have a cross feeding both branches with a capped nipple on the end. This would be so similar to #1 that using a cross isn't likely.

3. You could have a tee and an elbow feeding the branches.

4. You could have two tees feeding the branches with a nipple and a cap on the last tee

Of the four it is more likely to be #3 or # 4

It would be very interesting to know what the actual pipe configuration was and whether "dead " radiator was connected to the first or second branch coming up from the main. I agree with Gerry's theory of "going with the momentum". As to what causes the initial primary dominance of one branch over another, I don't know. I can see arguments for both the first or the second branch being dominant based piping configuration and/or position (being closer to the main or closer the end of the riser) I guess it's one of those things where you worry more about the fix than the cause.

I've seen weird things happen like this with hydraulics. That's why having a dual/separate supply lines is far preferable to siamesing units together on one line.

Might also be a something really off the "wall" (no pun intended) like Coriolis effect. (Maybe Aliens?

- Rod