Main vent modernization

steve_173

I used (pi)(r^2)(l). I’m assuming for now that 2.5” and 2” are ID. I have a split main. I didn’t include the header or short risers to the main. Does that get included somehow?



At 2” my spreadsheet gives me 0.0218 cf/ft (close, but different than the 0.023 cf/ft number seemingly from Gerry’s book). Is that right because proceeding with wrong numbers is a waste?



Ignoring a reducing elbow in each main:

1) 21.5’ @ 2.5” and 18.35’ @ 2” – 1.133 cf – currently a Hoffman #4

2) 8.67’ @ 2.5” and 42.81’ @ 2” – 1.229 cf – currently a Dole (can’t see the specific number, but it seems to be a larger one)



This is single pipe and the steam mains slop toward the returns. There is a T where the main comes in and then drops to the wet return with the vent right on top of the T.



What’s a good plan? How do I ensure some slope to the antler with threaded pipe? If I use a 45 elbow, the vents will not be vertical? Do I build it all with 3/4” and then reduce to 1/2” for the vent or is 1/2” simpler? Does the rise away from the T matter in the sense that higher is better or get it above the highest point in the main (6” is enough or more is better)? In one case (a wall) and maybe the other (piping) makes it impossible to bring the antler 15” back along the main. Which direction do I go in then? Perpendicular to the flow? Or must I tap the mains further back (assuming I even have space after the last T)? How much spacing should I leave between vents so that there’s room to turn them or swap in others at some point? Can I use Teflon tape or is something else better with steam?



I assume the Gorton leaking issue was a fluke. Do I go with a Gorton #2+#1 or two #2 and ignore the extra cost? If I mix the sizes, does the #2 come first on the antler?



Are these calculations impacted by the pressure setting?

nicholas bonham-carter

how much main venting?

of course air in the boiler risers, and steam chest needs to be vented as well.

instead of calculating the volume of the pipes, i would add vents until you get a back-pressure of less than 2 ounces. the use of 2 45 deg ells [together] will give that bit of positve slope needed on your menorah/antler.--nbc

steve_173

The additional volume

The additional volume probably isn't that great, but is enough to push the need to two #2s. It might be cheaper to just over vent it than play around. Excess venting won't hurt for the main.



What do I need to measure: risers, header, risers again? How do I divide that into the two mains as it's partially venting out of each main? Do I include where the header drops down until the water line? What about the space in the wet returns above the water line?



By steam chest, do you mean the space in the boiler above the water line?

Rod

Main Vents & Antlers

Hi Steve- You're "over calculating" a bit and making it too complicated. As long as you know approximately where you are in the ball park, you are okay. I'm assuming that each branch main has its own return and therefore you will need a main vent at the end of each one.  Since you have Gerry Gill's book with the venting tables you have all the info you need.

Antlers-  The antlers need just enough slope to "encourage" any water that gets into them to drain away from the vents.  If it's attached to a parallel flow main then run the antler uphill from the end of the main. That way it will slope in the right direction and also an water that enters the antler will have to do a 180 degree turn. Another way to put slope in the antler is to use two 90 degree street elbows attached together coming oiff the main.  In most cases 1/2 inch pipe works fine. 1/2 pipe will support 2 ea Gortons #2s. In a case where you need more venting that that then you could go to 3/4 in pipe.

Teflon tape works okay. Just be sure to start the wrap an 1/8 inch back from the end of the pipe other wise bits of Teflon tape might drop into the pipe and clog the vents. I'm assuming you have seen the antler diagram of Brad White's. Note the pipe union. This allows you to make up the antler on a bench and attach it to the main using the union which makes it much easier to install and service the antler. If you haven't done so already you might want to visit Gerry Gill's website http://www.gwgillplumbingandheating.com/

as he has a lot of good information on steam there.  Since you're into calculations you might want to down load the Burnham Heating Helper 

http://pro.usboiler.net/PDF/htghelper.pdf



if you don't already have a copy. It has lots of info and tables

- Rod

steve_173

Don't have the book

That number was sited as coming from Gerry's book. I don't actually have the book. I can't do a 180 as foundation wall is in the way. I could tap on the other side, but I'd rather avoid that. For the other main I might have to come back more than 15" to make it possible. Can an antler be too long? Is the ideal 15" to the first vent on the antler?



I don't mind the 3/4 if it keeps options open for later. There's not much pipe involved.



Two 90 street elbows or two 45s?



What about a more complex shaped to the antler? I could come out at 90 to the flow and then turn it another 90 or 45 keeping a slope. It could be tricky to get that right and tighten the coupler. I guess nothing has to be very tight.



I wondered about the teflon disintegrating. What pipe dope is appropriate? It seems some people like LOCTITE 30534.

Rod

Main Vents

Hi Steve - Use two 90 degree street elbows. This makes a "universal joint" and you then orient it in any direction you want. You don't have to make it complicated.  The 15 inch measure measurement is ideal though you don't see it often. Most vent come straight up at the end tee. The main concern is drainage of water away from the vents. You don't want the vent piping sloped so that water collects in the vent line.



Venting - Cubic Feet per minute @ 1 ounce of pressure.

Gorton #1 -       0.330

Gorton #2 -       1.100

Hoffman #75 -  0.500



Hoffman # 4 -   0.060    

Dole #5     -       0.065



The common rule is to have enough capacity to vent the mains within 3 minutes. As you can see the first three vents  are the contenders. The Dole and Hoffman #4, while still available, were used back in the days of coal fired boilers where steam pressure built very slowly so large capacity vents for fast venting weren't beneficial.

Keep in mind that the above figures are at a very minimum pressure (1 ounce per square inch)  As more steam is produced the venting rate increases rapidly.

- Rod

steve_173

Make a rough "S"

I think I got it. Use the two 90s as a way of decreasing the splash and hinging the antler to get a slight slope? I probably have space to have the first 90 turned back against the flow or close to it.



Are you saying that at actual pressure, one doesn't need as much venting as is being proposed?

Rod

Main Vents

I'm not sure what you are referring to as "actual pressure". When the burner turns on cold steam pressure starts at zero and builds from there. What I'm saying is that when the pressure is at one ounce, each of the vents will pass the indicated amount of air. As the pressure increases the vents will pass proportionately more so if you have adequate venting at one ounce you don't need to add a fudge factor as extra venting will be supplied by the increase in pressure. For and example= At 3 ounces of pressure,  the Gorton #1 and the Gorton #2 pass twice as much air as they do at one ounce.

- Rod 

steve_173

Proper size

Right, so I'll size it to the volume with the 1oz rating. What I was suggesting is that if a #2+#1 is not enough, it might not pay to add additional #1s and instead jump to two #2s.



To get the right size, I need to figure out what I've not included in the mains' volume: boiler and near boiler piping before the main and then how to divide that between the two mains? Other than the piping, how can I estimate the rest?



Is there a table or simple way to get the volume of an elbow? Reducing elbow?



Do I include air above the water line in the wet returns?

Rod

Main Vents

Hi Steve- Again I think you are "over calculating". I would just put a Gorton # 2 at the end of each main branch and call it a day. That will be a huge improvement over what you have now. I've attached a drawing of a low profile antler. As you can see it is easy to add more venting later if need be by just adding another tee and a another vent on the end of the present vent tee. If there is room, you can also use a longer nipple between the main and first elbow to raise the whole "Antler" higher.

I might mention that Gerry Gill's venting tables are included in the book "Greening Steam"

http://www.heatinghelp.com/products/Steam-Heating-Books/25/158/Greening-Steam-br-How-to-Bring-19th-Century-Heating-Systems-into-the-21st-Century-i-and-save-lots-of-green-i

or they can be got separately in Gerry & Steve's venting book.

 http://www.heatinghelp.com/products/Steam-Heating-Books/25/146/Balancing-Steam-Systems-Using-a-Vent-Capacity-Chart-by-Gerry-Gill-and-Steve-Pajek

Either way they are very worthwhile to have.

- Rod

steve_173

I see

How will I know if I need more venting?



Is the antler necessary with just one vent or can I just bring it up higher with a nipple?



I could leave the old vents behind the Gorton #2s for some extra venting for only the cost of some pipe.

nicholas bonham-carter

While you have your pipe wrench out,

Get a good 0-3 psi gauge, and put it on next to the pressuretrol, and you will see when to stop adding vents. The pressure should only be an ounce or so as the boiler is first firing and all the air is escaping. If the pressure is higher, then it shows resistance to the escaping air. This means you are paying for extra fuel to force the air out.--NBC

Rod

Main Vents

I wouldn't even bother with the old vents as even new they have very small venting capacity.

Sure you can just use a long nipple and mount the vent on that. Using the antler just makes it easy to add extra vents if you decide to do that. As NBC mentioned a low pressure gauge will tell you if you are getting back pressure from not enough vent volume.

- Rod

steve_173

Guage range

Which gauge range is best? Some here use 0-15oz, 0-20oz, 0-3psi?



I wonder why Slant/Fin includes a 0-30psi gauge. It also has some vacuum readings. Maybe they needed both for some customers.



If I go straight up, get it as high as possible?



How does the ability to vent change with pressure? If the vent can move 1 cf at 1oz, what happens at 2 oz, 3oz, etc? Is it linear?