Spitting Air Vents

DNW

I have a 2-pipe (?) steam system with recessed convectors.  I have four Hoffman No. 4A vents at the tops of vertical pipes near my home boiler.  Three of these vents have started spitting water up to the basement ceiling; the fourth does not.  This happens when the boiler has been on for a long time, as when heating up in the morning when the thermostat setting is increased.  When the boiler cools, I can hear air being sucked back into the valves.  Also, when the boiler is operating, the water level in the sight glass fluctuates up and down quite a lot (about 3 or 4 inches).  Any clues as to what's causing the spitting? 

Thanks,

DNW

BobC

Pressure, calcium deposits

First, do you know what pressure the boiler is running at?



It sounds like calcium deposits are probably preventing the Hoffmans from closing all the way. Knowing what the Hoffmans cost, I'd replace them with Gorton #1's and then try to reclaim the Hoffmans as spares by boiling them in white vinegar for 15-13 minutes.



Last year my Ventrite 35 did the same thing and the vinegar boil allowed me to reclaim it and use it as a spare after I replaced it. just make sure everything is relatively cool and shut the boiler off before getting out the wrench.



Take some pictures of the boiler, the piping around the boiler, and those vents from a couple of different angles and post them here so we can see what you have.



Bob

Big-Al_2

Surging

It sounds like your boiler is surging (boiling violently) and sending water up into the main.  This could be caused by dirty or oily water.  Has there been any new piping work done lately? 

Brian_74

Similar situation

I'm not sure if this helps, but I'm having a similar problem, although with Hoffman 75s. Mine were installed less than a year ago and one does occasionally let out water. I've found that if I catch it when it's just starting, a tap with a mallet stops it. I did the boil in vinegar route, which solved the problem for about a week, maybe 10 days. My sight glass shows no surging, so if we're having the same problem, it's caused by something else. Of course, you should take care of the surging.

Charlie from wmass

Brian check the ports

for your sight glass. I have seen many steady waterlines that were only steady because the sight glass valves were clogged. Are the vents at the drop or back from the drop of the return pipe?

Brian_74

It's only 1 of 2

Hi Charlie,



The waterline isn't perfectly steady, and it definitely bounces up and down when I do the weekly blowdown.



The vents are at the drop, but about 1 foot above it and then at a right angle. It's a very short menora. There are two Hoffman's there, and only one has the problem and like the original poster, not every time.

Charlie from wmass

Could also be

a sluggish return holding back the condensate.

Brian_74

Maybe

but it just seems like it's a vent closing too late. I've got some Gorton's on order so I'll be able to swap it out and see.

DNW

Spitting Air Vents - System Pix

I believe the system operates at about 2 psi.  Here are a couple of pictures with the spitting vents (2nd picture, just below the yellow "2 psi" sign (nat gas pressure).  We've had a bit of pipe work done over the past few years.  We just noticed the spitting vents this season, although they've likely been doing it for a couple of years (we could hear odd sounds, but didn't notice the spitting).

Thanks for all the help!

Dave in QCA

pressure too high

I have been looking over the pictures of your system.  It appears to have been a trane vapor vac system.  The alternator receiver appears to be the Trane type, but it looks as though it has been abandoned in place.  The sight glass is gone, and there is not vent on the top.  Plus, you have a vent at the "dry return end" of both of your steam mains, as well as a vent in each of your 2 dry returns on your condensate return lines on your 2-pipe system.

Since it appears that the old alternator receiver is no longer functional, you are depending on gravity to get the condensate back into the boiler.  That works just fine until you begin to build pressure.  Gravity return on a 2-pipe system deal with something that is called the "B" dimension.  The B dimension is the height of your return piping above the water level in the boiler.  The return piping is measured right at the point where it dropps down to the boiler because that would be the lowest point.  The B dimension must be 3" in height for every pound of pressure in the boiler.  So, if your boiler is set to allow pressure to climb to 2 psi, the B dimension would have to be 60" or greater.  If it is not, the condensate will be held back in the return piping causing the vents to squirt and a drop in the water line of the boiler.

Recommendations:  1 - Turn down the pressure!  You have an old vapor system that was designed to run on 8 oz of pressure or less.  Make sure you are running at 1 psi or less.  2 - The vents are probably all limed up, and their are not adequate for todays venting standards.  We don't know how long or what diameter your steam mains are, but I would considere replacing the 2 steam main vents with Gorton #2 vents and the 2 Return line vents with Gorton #1 vents.   This should make your system purr.

Dave in QCA

NO COPPER ON GAS!!!!!

I also see that there is a nat gas line coming to your water heater that is piped in copper.  This is not allowed!!!   Also, it is unusual to see distribution inside a dwelling at 2 psi., however, there is a regulator there to bring the pressure down to the proper level for the water heater.

You should hire a plumber to replace the copper with black iron pipe.  Copper has been known to corrode from the smell additives in nat gas. 

DNW

Trane Trap

Dave, thanks for the input.  Here's a picture of the ancient Trane Direct Return Trap.  It's still connected, and appears to be in use (there's a hole in the vertical pipe coming down from the trap, and it spouts water quite freely unless I keep the bike inner tube wrapped around it!).  Also, the vents are 50" above the marked line on the water inlet float body. 

I went down this morning during the heatup, and the two vents that were spitting were cool; the third, that sometimes spits, got warm and continued to vent a little steam.  The fourth vent, on the hottest pipe, just continues to vent steam (small amount, but audible hiss). 

Our house has 20 convectors for about 3500 ft² - two stories.  Piping to the farthest unit must be at least 60 - 80 ft.

I think the vents probably do need replacing.  As far as boiler pressure, I'll have to call someone in - the same outfit that replaced the inlet float a couple of years ago.  I don't think they'll understand much of what you describe!  I haven't really found anybody around G'boro who seems to know much about these systems... they just want us to convert to forced air!

DW

DNW

Copper / Gas

Dave -   Thanks for the tip.  Copper may be allowed here, but I'll ask the guys when they come in about this.

DW

Dave in QCA

correction

Here is a link to a publication that shows the components of the Trane System. http://www.heatinghelp.com/files/articles/1392/26.pdf



I was remembering wrong, there was never a vent on your Trane Direct Return Trap.  The vent line from that device ran to the return piping, and the vent locations that your currently have are original, just the vents have been changed.

If the return trap is functioning correctly, there is not a buildup of condensate because the return trap is putting it back in the boiler.  The way it does this, condensate enters through the bottom pipe as condensate is flowing from the system, but because of boiler pressure, cannot flow into the boiler.  Air in the return trap is vented to the pipe leading to the return piping, which in turn is vented.  As the return trap becomes full, the float rises, and at the maximum point it will click the valves located at the top.  Simultaneously the vent valve closes and the steam valve opens.  Now, the return trap is at the same pressure as the boiler and the condensate can flow by gravity back down through the bottom pipe, and through the check valve into the boiler.  As the trap drains, the float drops, and the valves snap back into the normal position.  The steam valve closes, the vent opens.  Pressure from the boiler tightly closes the check valve in the return piping below, and now, condensate can flow from the return piping and into the trap again.



Your return trap may or may not be functioning, but at any rate, you need to replace your vents and turn your pressure down to a cut out pressure of 1 PSI.  This is the absolute maximum that this system should be operating at, and it was designed to run even lower.

DNW

Air Vents?

Thanks again, Dave, for the great info!  The Trane document shows "quick vents" and "float vents" on the lines near the boiler (pg 11).  My system has four Hoffman No. 4A QuickVents only.  The Trane doc says their quick vents "close against steam only", while float vents "close against steam and water".  Do you know if the Hoffman Quick Vent is designed to stop water (ie - has a float?)?

Dave in QCA

Hoffman 4A is float & thermostatic

Your Hoffman 4A vents are both float and thermostatic.  Here is a link to the Hoffman Specialty page with main vents.

http://www.hoffmanspecialty.com/pdf/hs900/HS900-steamall.pdf 

 I would imagine that your original float type vents were on the return pipes.



Your existing vents could be cleaned by soaking them in lime away liquid cleaner.  However, they are very inadequate and do not come near the venting capacity of your original Trane vents.   If you notice some of your radiators heating more than other, this could be the reason why.  Additionally, you are probably building unnecessary pressure in your system way before it is fully heated, thus costing efficiency and fuel.  I would recommend that you replace all of your vents with Gorton #2 vents.

At 1 oz of pressure, the vent capacity is as follows:

Hoffman 4A    .133 cfm

Hoffman 75     .5 cfm

Gorton #1       .33 cfm

Gorton #2      1.10 cfm

Trane cast iron bullet style (obsolete)  .780 cfm