Can steam mains be over-vented?

Jon Held

They are both 2" pipe. They add up to around 73', using my measurments for the insulation order. Keep in mind that doesn't include fittings. There are 9 convectors in the house so add in 9 t-fittings, 7 elbows, 2 unions, and 1 or 2 couplings. Not bad for off the top of my head, but you want to know the length of each run, don't you? Can't give you that until tonight.

Jon Held

Pretty much sums up my question. Is there such a thing as "too much" venting for steam mains and convectors? For example, both my mains currently have Gorton #1s installed. I ordered a pair of #2s to move things along as quickly as possible and I was thinking that I might add the #1s on a small manifold on the mains.

steam on brain

over venting possible???


On my 2 pipe Richardson Vapor System, there is only one vent, a Gordon No. 1. I removed it recently to see what will happen, as I was pondering the same question you are...I do not see any difference yet, except for the reduced sound of the air escaping.

The Gordon vent is mounted on a bucket trap. I never see steam at the vent. I wonder if the mains are filling, as they theoretically should be. It was a coal fired system which was replaced by a Weil-McLain gas gired boiler (250k input) in 2006.

It cycles on for about 20-30 minutes and seems to be performing very well. I will have to study the venting closer. I'm no expert, but I do not think you can over vent the sytem I have. I realize there should be a device that would close off if steam ever reached that point, but if steam is not getting there during the on cycle, I do not see any reason to constrict the vent.

Hope some experienced members can comment.

Coal Man in PA

Jon Held

The purpose of any steam vent (main or radiator) is to allow air out and close with steam. When the boiler stops firing and the steam condenses, the valves open again to allow air back into the system. From what I have read so far, the faster you allow air out, the faster the steam gets to where it needs to be. There are limiting factors like pipe insulation and location, but all things being equal, the larger the hole, the faster the air moves in and out.

What I'm trying to accomplish is to get the steam where it needs to be in the shortest amount of time by properly insulating my mains and near boiler piping, increasing the main vents to Gorton #2s, and possibly changing all my convector vents throughout the house.

Steamhead (in transit)

Jon, has Alex

measured your mains? If so, how long and what pipe size are they?

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Steamhead (in transit)

OK, I'll look for them

later tonight.

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Matt_67

Sorry it took so long for this Steamhead. The mains are 52' on the long side 31' on the short side. All 2" black pipe. Both mains are now each vented with a Gorton #2. I added 2 elbows and a 6" nipple to isolate each vent from any stray condensate that might be shooting down the mains. All 3/4" black pipe as well. The main vent extentions are not insulated.

Steamhead (in transit)

If you add

two Gorton #1 vents to the long main along with your #2, that should balance out the two mains and the steam will reach the ends of both at about the same time- and very quickly, with only ounce pressures! Since you already have two #1 vents sitting around, all you need is the necessary tees and nipples.

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Matt_67

You are calculating the volume of each main and comparing it to the venting capacity of the Gorton #2...correct?
In my calcs I get 163.28 cu ft for the long side and 97.34 cu ft for the short side, but that is raw volume at 1 ATM. What is the venting capacity of the Gorton #2? I don't see this info on the Gorton website.

How are you making your calculations?

Unknown

Check your numbers, Jon

31 feet of 2" pipe can't possibly contain almost 100 cubic feet of space.

100 feet of 12" round pipe doesn't even contain 100 cubic feet of space.

Noel

Matt_67

Duh. Math was wrong. I took cubic inches/12 for cubic ft as opposed to cu in/1728. Beginner mistake. Sorry 'bout that.

Long main is 1.13 cu ft
Short main is .68 cu ft.

Dave_4

I do not know the answer but...

I'm sure Steamhead does.

My "concern" is this:

We know fast venting some things is a bad thing. This is evidenced by fast venting SFT (Fin Tube BB designed for steam). The steam travels so fast the slope becomes inadequate to handle the reverse directioned condensate. The solution to that problem? Convert the SFT to two-pipe and reverse the pitch to allow steam and condensate to travel in the same direction. The second solution? Simply vent more slowly.

The down side to slower venting in this example (granted this example of SFT is NOT like a main vent issue) is the room has a steam emmitter that is slow to heat - inducing a cooler than "normal" output based on the time it is filled with steam - vs. the time it takes slow venting to allow it to completely fill with steam. On a cold day, when the boiler run-time will make the minute or so delay insignificant on the slow-vented SFT, no problem. But on a fall or spring day, the boiler may be satisfied in 5 or 10 minutes. Then, the lost output of a slow-vented SBB or any emmitter for that matter, is substantial!

Might the same dynamic exist in a main (or two)?

I DO know slow venting of a SFT emmitter eliminates hammer and banging - not to mention "spitting" almost every time!

I suspect over-venting is so rare, none of us know the problems it can cause. But as in all things "steam," Dead Men had a few secrets we still are not privy to - despite all Dan has furnished in that regard!

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Steamhead (in transit)

That would be more likely

on a counterflow main (or a very long radiator runout that needed a vent), since the condensate would have trouble draining back against incoming steam.

Here, the mains are parallel-flow, so that shouldn't be a problem. Provided there aren't any sags in the main and the return connection is not restricted, no condensate can collect and bang.

I once started up a system where someone had disconnected a radiator without telling me. This rad was the last on the main and had not been moved out of position. The steam flew down that main to the open runout, but did not bang. Got a bit humid in the living room though :-0

"Steamhead"

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Dave_4

I understand Frank...

But wouldn't the ability of the condensate to drain, when extreme venting occurs, be thwarted by virtue of the sheer volume of condensate within the main - "reducing" the effcetive pipe size - be a factor?

I can see a micro sunami cresting inside the main, moving at 30 MPH crashing into the (typically located in the wrong place - end of main) vent, and wreaking havoc on the vent and the dime size orifice spewing water and spitting all over the place.

Remember, low pressure steam runs fastest. EXTREMELY LOW PRESSURE steam runs faster still! Do we really want steam moving at warp 3?

I still hold we can "over-vent." Missing a radiator union, left wide open, is a totally different example than a wide open main. One occurs on a branch. The other impacts the main; all of it.

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