main vent question

steamychick

I am going to get (2) Gorton-2's for my main, but on an earlier thread someone said to still use my existing Hoffman-75 as well. Would it be better to just replace the old Hoffman with another Gorton-2? I am thinking so, because it seems more is always better when it comes to main venting from what i've been reading here. Also, the pipe that is tapped in to the main with the old Hoffman on it is incredibly small-smaller than the diameter of a straw. Seems like it would restrict the air flow going in to the vent. Should this be changed? -Thanks

MTC

Re: main vent question

Sounds like you have a 1/8" tapping. Changing your vents will do no good until you fix that. If this is a reasonably large main (2"+), I think you'd want to see a 3/4" tapping. This would allow you to use up to 4 Gorton #2s to achieve maximum venting. Or 3 and your hoffman, or whatever you choose.



To get any value out of your 2 Gorton #2's, you'll need a 1/2" tapping. If you're going to bother doing the work, I'd just go right to the 3/4". Then menorah your vents on 3/4" tees, and plug the end of the last one. You could do your 3 vents this way, and if you want to get to maximum venting later, pull the plug, add a couple more tees, and a couple more Gorton #2s.

MTC

main venting

It should be noted, that my response was an easy answer based on incomplete information. To properly size your vents, you'd need to add up the total length of each size of pipe in your steam main, use that information to calculate the cubic feet of air in the main, and then aim to vent it out in about 1 minute.



A Gorton #2 will vent 1.75 CFM at 2oz pressure. A Hoffman #75 will vent .75 CFM at 2oz. If this is a smaller system, getting it vented out in 1 minute at 2oz should be sufficient, but keep in mind that you start at 0oz when venting out the mains. At 1oz, those CFM ratings drop to about 2/3 of the 2oz ratings.

steamychick

thanks

My main is 3" x 31'. I didn't notice how tiny the tapping was because the old asbestos insulation kind of overlapped it. Sounds like I need the 3/4". The other issue is that the tapping/main vent is at the end of the main pipe. From what I've read, shouldn't it be moved to about 15" in from the end? Or would it be o.k. to leave it where it is, change the tapping to 3/4", and then add the menorah 15" in from the end?

MTC

15" in from the end

would be a much better location. While fairly common, having it right at the drop to the return puts it at much greater risk for water hammer damage, and greatly shortens its life. Since you're already re-tapping, i'd move it roughly 15" in and either leave the old vent in the 1/8" tapping alone, or plug it. If its functioning now, I'd be inclined to leave it until it no longer does and plug it then.



On your menorah/antlers, make sure that the pitch of the antler bar drains any water that does get up in there. If it collects in there, your vents will either not vent, or spit water, or just get damaged by the water. This typically means go up as high as you can (6-10" if possible), and elbow back toward the boiler, as your main likely is pitched away from boiler. This way water drains out of the antler bar and back to the main and into the return.



You have about 1.65 Cu Feet of air in your main, call it 2 Cu Feet to allow for near boiler piping and make things easier. To vent that out in 1 min at 1oz, you'd need 2 Gorton #2s, so sounds like you're on the right track.



My suggestion would be to tap it 3/4" its not that much more work than 1/2" and gives you options. Then come up as high as you can (gortons are tall, so be careful how high you go) to an elbow, a short nipple, 3/4" tee, another nipple (you want to leave enough room between the Tees to be able to spin out the Gortons individually), another tee, and a plug in that tee. This way, if you ever decide you need more venting, you simply pull the plug, add another nipple and tee, reinsert plug, and you're done - don't have to tear apart what you've already done. Also, if there's ever any junk in there, you can open that plug at the end and clear it out. Some would advocate putting a plugged tee instead of an elbow on the top of the riser nipple as well, so that you can open both ends to clean it out if necessary. Its not a bad idea...

steamychick

MTC-worth your weight in gold!

Excellent point about making sure the pitch of the antler bar will drain any water away! Also a great point about leaving enough room to be able to take the Gorton's off! I am going to wait until I have the Gorton's in hand before I start to do anything so I can make sure of distance,etc. You have a great way of explaining this! ...maybe a future in writing how-to manuals? :-)

MTC

Haha, thanks

but the credit mostly belongs to Dan Holohan. I've poured over his books, and he explains things so well, I'm mostly just regurgitating. If you don't have some of his books, I highly recommend them.



Good luck with your project!

steamychick

regurgitating important info.-a.k.a.-cliffnotes of steam

 I have 2 of his books. He is great at explaining things! But sometimes it's nice to get real-time feedback and advice before jumping in. My dad instilled the old measure twice, cut once way of thinking in to me. Sometimes it makes me feel more sure of myself to measure three, four, and maybe even five times when it comes to things I'm just learning about. I know, I know,....can you say overkill? :-) Occasionaly I suffer from paralysis by over-analysis...