Main vent replacement

Gerry G

Wanted to get a sanity check here first.

A little while ago one of the three main vents started hissing a bit. Today after a full flush of the pigtail and a system clean out, the vent was hissing like mad for the entire duration of the boiler cycle. This main is the one nearest to the boiler, but at the end of a long return from one of the uptakes. The vent is a Hoffman 75, and is about 8 years old. (Image attached)

After reading the threads here, my guess is that I need a new vent. But also wanted to check if there's anything else to look out for.

nicholas bonham-carter

You need a bigger vent-at least one or two Gorton #2's in addition to the Hoffman which is probably still working, but undersized for the job of getting the air out of the pipes and boiler in under a minute or two.
What size and length is your main?
Check your pressure with a 0-3 psi gauge, to make sure it is low enough, and insulate the pipes.
Was the boiler ever skimmed?--NBC

Gerry G

Thanks for the quick reply

Main #1 is for the front of the house, and is in a loop, with a Hoffman 75 vent at the turn of the loop and with another Hoffman 75 (the hissing one - The one that is in the picture) at the end of the return close to the boiler - 80' total length (40' x 2), 3" pipe diameter.

Main #2 is for the back of the house, and is a straight run, with a Hoffman 75 vent at the end of the run - 40' total length, 3" pipe diameter. The condensate return on Main 2 runs along the floor.

Everything was working fie until this season. The last time the boiler was skimmed was during the original install years ago.

Steamhead

Start with two Gorton #2 vents on the long main, and one Gorton #2 on the short one. If this setup appears to be too small (hisses loudly during venting), add more vents, but always have twice the capacity on the long main as on the short one.

This is assuming that Main 1 is 3" for the full 80 feet.

Gerry G

The return leg of the 80' main looks to be 1" smaller than the uptake.

Gerry G

Reskimmed the boiler. There was still black run off from the skim port. Cleaned the boiler again, but the hissing is still going on. The Gorton valve arrives on Friday, so hopefully that will solve it.

Fred

I just had the same problem with one of my Hoffman 75's. I noticed a couple days ago I lost about a half gallon of water in the boiler, over a 5 day period, and started looking for a leak somewhere. I happened to be in the basement yesterday and in a back room where I have 4 Hoffman 75's on the end of a main. While the boiler was running and had been running for about 25 minutes (weather has been bitterly cold here, around 0 with wind chills around -10) one Hoffman was hissing. Usually they are all but silent. I tapped it, thinking it would close but no such luck. Didn't seem to be spewing steam, that was obvious, but what else could it be doing but letting steam out. When the boiller shut down, I switched out the vent for another one I had on hand and my water level has been good. Just goes to show how hard it is to find a leak when you can't even see steam exiting from a vent. The vent in question is only two years old. I have some that are 10 years old and doing fine. Sometimes things just fail. I suppose I could try to soak this one but it seems better to me to just replace it and be done with the problem.

Abracadabra

You skimmed from the top not the bottom right? Picture of your skim port please?

Gerry G

Definitely from the top.

Having trouble posting images. (is there a size limit?)

Gerry G

Gerry G

Finally, got the image to load - Skim port:


Update - Gorton #2 arrived and I installed the Gorton & Hoffman off a tee. Boiled the Hoffman in vinegar just in case. Ran the system, but sure enough the Hoffman kept spewing steam when the system got hot enough. Sounds like I'll be plugging the Hoffman riser and ordering another Gorton.



Did a lot of boiler flushes too and probably will need a round with TSP next.

Thanks for all the help.

Gerry G

Update - Part 2

A week ago replaced the hissing Hoffman with a Gorton #1, so I have a #1 & #2 on the antler in the pic above. Everything worked fine.

But now, the second Hoffman 75 in the middle of the long main started to hiss when the boiler runs for a long time. I put in a new low PSI gauge and the vent hisses when the gauge reads 1PSI. That's also when the system shuts down.

Pressuretrol is set at .5 - 1 differential

Fred

Does it hiss the entire time the boiler is running or just at the point when the boiler shuts down? If the entire time, the vent may be bad or need cleaning. If only when the boiler shuts down, it could be a slight vacuum causing the vent to open and suck air into the main and vent may be ok.
Why do you have a vent in the middle of the main? Placed there, they will close earlier than they should and you won't get the full benefit of it being open longer, at the end of the Main. Additionally, it will likely stay closed longer.

Gerry G

It hisses after a long boiler run time, towards the end of the cycle and keeps hissing after the boiler shuts down.

As for why it's in the middle of the run - have no idea, a vent was always there since we moved in 16 years ago and the HVAC guys replaced the old vent with the Hoffman #75 when they replaced the boiler in '05.

Should I cap that vent and add another vent at the end of the run?

nicholas bonham-carter

Yes-move that vent to the end, and add another.
Generally, a pressure check is in order if any main vent hisses.
If the main, or radiator vents are hissing after shutdown, it is a sign that the main venting is inadequate, as the relief of vacuum is one of their jobs.--NBC

Gerry G

OK, will do and report. Some radiators are hissing after the system shuts down.

Fred

After long boiler runs, especially if the boiler has short cycled a few times, when the boiler finally shuts down and the steam collapses, the space that the steam occupied has to be filled with air and sometimes the vents can't/don't open fast enough to fill all the radiators and piping, creating a temporary vacuum. That causes the vents to suck air, making the noise you hear. Having your main vent(s) in the middle of the main compounds that problem. Do move them to the end, as has been suggested. More Main venting may help, especially on normal heating cycles. There still may be a little vacuum/air suction on long and/or multiple short cycling but it isn't going to hurt anything.

Gerry G

Removed the vent at the mid point of the long main. Put it in the antler at the end - now have Gorton 2, Gorton 1 & Hoffman 75 at the end

Replaced another Hoffman 75 with a Gorton 2 on the shorter main.

Hissing from the mains is now gone. Boiler shuts down when pressure hits about 1.1 psi.

Now on to rebalancing the system. Added a large radiator when we did a renovation that has a 1" supply running about 25' to it. Radiator needed to be super big because it needs to heat a large area. But this radiator took a long time to get warm compared to other radiators.

After reading Dan's book, realized that this line wasn't purging enough air fast enough. Have a Ventrite #1 on it. Ordered a Gorton D and will see how the replacement works.

BobC

A 1" pipe can only supply an EDR of 28 unless the feed is dripped so condensate does not flow in the same pipe. i suspect your radiator may be larger so you have to think about running a larger pipe to feed that large radiator.

Bob

Gerry G

I know it's not ideal, but the contractor used copper for supply, so the 1" line has a larger inside diameter.

Steamhead

Gerry G said:

I know it's not ideal, but the contractor used copper for supply, so the 1" line has a larger inside diameter.

The contractor told you that?

He's wrong. 1" inside diameter is the same for steel or copper.

I guess you never hear it all......................

Gerry G

What can I say?

Steamhead

Say to the contractor: Get back here and put in the right size pipe.

What size is the radiator?

Gerry G

19 sections - 20" x 7" x 2" each 45" total length

KC_Jones

That radiator has an EDR of around 38, the pipe isn't big enough to supply the required amount of steam AND it shouldn't be copper pipe. A Gorton D vent is huge and most likely won't help if you are trying to use the full capacity of that radiator because of the choked down pipe. Sometimes a big vent like that can cause more problems than it solves. Sounds like the person that ran that pipe didn't have any idea what they were doing.

Gerry G

The radiator fully heats up after the system runs for about 30-40 minutes. When I took the Ventrite off, it obviously heats up much faster, that's why I thought of putting in the Gorton D to evacuate the air ASAP, since there's also a very long supply line to it.

How would a drip feed work? Running a tee that catches the condensate and lop it to the wet return?

BobC

You might try putting a D vent just before the radiator input to get steam to the radiator quickly, then use a normal sized vent on the radiator itself.

A drip would come off the bottom of the pipe just before the radiator so the condensate would drop down, it has top go below the boiler waterline and connect to the wet return of the boiler. That almost doubles the steam carrying capacity of the pipe. Of course you could just pipe that large radiator as a two pipe radiator.

Bob

Gerry G

Regarding the suggestion to put the vent ahead of the radiator - I'm trying to figure out the physics behind it.

Isn't the goal to get maximum air out as fast as possible through the radiator, so shouldn't the big valve be at the end of the radiator to help evacuate as much air as possible?

BobC

If you want even heating across a steam system you want t the mains as fast as you can and the radiators slowly. That should make everything heat up at the same rate.

Venting the pipe that feeds the radiator (by placing the vent just before the radiator or by putting another vent on the valve end) can help if you have one radiator that heats slowly.

Bob

Fred

The only air a vent ahead of the radiator is going to vent is the air in the run-out to that radiator. It will close when steam gets to it and the radiator vent will vent the air in the radiator. All of these options are attempts to resolve a problem created by having a 1" supply pipe. They may work but I doubt it. When that vent closes, it will stay closed until the steam stops. While the boiler is running, both steam and condensate will have to return through that 1" pipe.
Do yourself a favor and put a 1 1/4 inch supply pipe in and be done with it. JMHO

Gerry G

I guess that's a job for the summer. The take off will be tricky.

Fred

Gerry G said:

I guess that's a job for the summer. The take off will be tricky.

What will make it tricky?

Gerry G

I'm guessing the reason the contractor went with copper was due to the ease of install.

He tapped into an old take off that's been plugged, then took two 90 degree turns plus a 45 to position the supply to run to the radiator. After the pipe was put in, the AC guy ran his metal ducts over the steam, so to access the takeoff, the AC ducts have to come down.

The supply can run a straight line to the main, but the main would have to be cut an a new take off installed.

Fred

I understand your situation but, you need to change that pipe, sooner or later, the duct will have to come down anyway. Copper is not used on steam lines because there is so much expansion/contraction with each heating cycle that the joints will eventually crack and leak.
The contractor did what was easy for him (maybe he didn't even know) but you need to do what is best for you. Use 1 - 1/4" black iron pipe and you will be good for as long as you and the next generation, maybe next 2 to 5 generations, are there. Besides, the 1" isn't working anyway. It has to be changed. Might as well do it during warm weather rather than have a crisis in the dead of winter.

EDIT: It doesn't have to be a straight run. Tap into the same place he put the copper.

Shalom

BobC said:

A drip would come off the bottom of the pipe just before the radiator so the condensate would drop down, it has to go below the boiler waterline and connect to the wet return of the boiler.

I'm having a similar problem. Huge radiator (maybe two of them), not enough pipe, the gargling in the pipe is quite audible at night and even can trigger the LWCO because most of the boiler water is suspended in there. As soon as the pressure drops off, the water runs back out of the pipe(s) and I wind up with another two inches in the sight glass. (Yes, the pressuretrol is set at 0.5/1.0.)

So, question. When you put this drip line in, do you put it before or after the radiator shut-off valve?

Also, why does it have to drop all the way below the waterline in the boiler? I'd think all you've got to do is block steam from getting in that pipe. I've got dry returns; if I looped under and attached the drip line to the bottom of the return instead of the top, it would fill with water and block steam, no? Or maybe use a pigtail, or a J-trap like a sink drain has, and attach it to the top (or 45° offset like the feed has)?

Fred

What size are those rads? What size is the feed pipe? Is the pitch adequate? I'm thinking that even though you have the Pressuretrol set correctly, the pigtail or the tapping the pigtail is in is plugged and the Pressuretrol can't control the pressure to its set points. Either that or the Pressuretrol has failed.