1920s Steam System - How to Add Main Vents

eddymoney · October 21

Hi,

I'm by no stretch a master at steam heat, but it's been pointed out to me on several occasions that the "main vents" in my steam system(s) have been plugged (I say systems because I have a duplex with separate boilers).

Long story short, I am wondering if A) it's a good idea to replace the plugs with new main vents (something like this) and B) what are the proper fittings and vents that I need in order to properly install main vents again. In one of my units it appears that there is only one plug, in the other it appears that there are two spots that have been plugged. Should any and all plugs receive a new vent?

Please see the images below:

Unit A:

Unit B:

mattmia2 · October 21

if it is a 1 pipe system and there are no vents on the dry return somewhere then it needs vents where those plugs are but the parts of the asbestos that are falling apart need to be dealt with first.

109A_5 · October 21

If there are no other main vents in your system, you would most likely benefit from installing main vents. Have you inspected the actual far end of the mains for vents. At the pipe transition from steam main to steam main extension, often called a dry return (typically the farthest point away from the boiler).

If those (pictured) pipe plugs are removed and those tappings are used the main vent should be offset vertically then horizontally so to minimize any damage from water hammer. Main vents usually have 1/2 or 3/4 inch pipe threads.

If there is more than one main from a single boiler, each main should be vented to best balance the venting of the steam mains.

Gorton #1 and Gorton #2 and Barnes & Jones Big Mouth BJ-2BM / BJ-3BM are popular main vents.

eddymoney · October 21

https://forum.heatinghelp.com/discussion/comment/1868638#Comment_1868638

Does this installation look correct (just found this on youtube)? It has a small horizontal fitting, a 90 degree fitting, and then the vent itself is installed.

mattmia2 · October 21

It should have a taller riser, ideally around 8"-10"

eddymoney · October 21

https://forum.heatinghelp.com/discussion/comment/1868669#Comment_1868669

If I'm understanding correctly, from the dry line I should go:

Short pipe meeting size of plug diameter
90 degree fitting
8" - 10" riser
Bushing
Vent

Or combine 1. & 2. with a male to female 90 degree fitting

eddymoney · October 21

Do you know of any thermal grade wrap that I could put on there? I believe that's what my inspector recommended way back when I bought the house.

eddymoney · October 21

https://forum.heatinghelp.com/discussion/comment/1868638#Comment_1868638

How would I decide what size Gorton I use? or main line vent in general

109A_5 · October 21

Something like this. The amount of venting depends on the size and length of the main and if any balancing is required with multiple mains of different length from the same boiler. Fiberglass pipe insulation.

mattmich · October 21

» The amount of venting depends on the size and length of the main

I would rephrase that:

The amount of venting depends on the ability of the boiler to provide steam. When pressure builds up before the main is hot all the way around, then you know you need more venting.

The steam can only go as fast as it heats the main above the boiling point of water.. you need enough venting to accomodate that, and more doesn't help.

What @109A_5 is saying is true in the sense that the main is typically sized for the system, and the boiler is sized for the system, so ideally it comes to the same thing.

A Tee with two vents on it is a good idea in any case because when one fails you'll still have heat everywhere. Below is my setup, with one Gorton and one Maid-o-Mist main vent, and it's plenty for my 2.5" 80-foot-long main. The MoM is a screaming bargain and lets plenty of air out. I went with a Gorton first because that's what all the cool kids get.

cheers -m

Steamhead · October 21

https://forum.heatinghelp.com/discussion/comment/1868677#Comment_1868677

Measure the length and diameter of each main and post the figures here. We can tell you what you need.

109A_5 · 12:06AM

This statement is also system dependent.

" The amount of venting depends on the ability of the boiler to provide steam. When pressure builds up before the main is hot all the way around, then you know you need more venting. "

My system never goes over 2 inches of water column regardless if the main vent is used or valved off. The predominant benefit (main vent versus no (or poor) main venting) is with a hot main the steam will propagate faster, purging the air out as fast as possible, filling the main with steam as fast as possible.

You want enough venting so when the mains are hot the steam will fill the main as fast as possible. There is a point of diminishing returns. Since even with a hot main the steam will only move so fast.

1920s Steam System - How to Add Main Vents

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