Sizing main vents

Jim Franklin_2

Braved Boston traffic and grabbed a pair of #1s. They're definitely faster than the Vent-rites- I got steam to the end of the mains in 5 minutes!

I have 1.43 CF of mains, almost evenly split between two #1s so .71CF per vent seems like plenty.

Rads are next, they're a bit pokey as it takes another 10 to get heat from the hand valve to all sections, but there's a lot of thermal mass to heat up with 4, 5, and 6 tube rads. I ordered the venting chart book, thanks for the pointer.

jim

Jim Franklin_2

Sizing main vents

I'm trying to diagnose a slow steam heating problem and I'm looking at the main vents, since steam moves slowly down the mains, barely a foot per second. My piping is like this:

14' of 2", then it splits into 2 loops.
1st loop is 8' of 2", then 34' of 1.5" with a non-eccentric reducer.
2nd loop is 44' of 1.5", also with a non-eccentric reducer. For what it's worth, this loop also has a 1' rise at 45 degrees and a corresponding drop for about half the run.

At the end of each loop just before the drop into the wet return is a Vent-rite 77. They seem clean but offer a bit of resistance to my lungs. They were also both loose where the cap fits over the body.

Is this enough main venting (without the loose caps ;-) I put insulation on the mains but that made little difference.

Is the loosening caps a common maintenance item or were they just not cranked tight enough initially? I don't hear any hammer that might loosen them.

thanks...

jim

chuck_6

Sizing main vents

Jim:

I would use Gorton vents on the main. It sounds like you need a Gorton No. 2 on each main. You may want to call Ken Kunz at Gorton. Gorton's phone number is (908) 276-1323. Ken is very helpful and can give you guidance.

If Steamhead replies, listen to him because he really knows venting.

Chuck

Steamhead (in transit)

Thanks, Chuck

for the kind words.

Jim, I'll second Chuck's recommendation of one Gorton #2 vent per main. The Gorton #2 makes the Vent-Rite #77 look like a toy. If you can't find Gortons in your area, call Ken Kunz or Linda Mast as described above, and they will see that you get them.

Jim Franklin_2

Gorton #2s

are like hen's teeth where I am...I spoke with the local rep and he said he sells 5 a year and the #1s would be easier to find. The #2s are a 1/2" thread and I have 3/4" now, plus I don't have the ceiling clearance for the #2s so I'd have to swap in 6" nipples. Is it worth all this to get the #2s or will #1s do a decent enough job? The #1s are also much cheaper.

many thanks...

jim

michael_15

#1 vs. #2

A #2 is equivalent to four #1's, so you'd need a good pile of them to match the venting capacity of the #2.

-Michael

Bob W._3

You would have to measure the volume to compare. I have larger and longer main vents than yours and used 2 Gorton #1's on each. However, I did the calculations first, using Steamhead's data. YMMV. You can get them here:

http://www.statesupply.com/displayCategory.do?Id=1817

Bob W._3

From a 12/8/01 post by Steamhead:

Hoffman #75 or Gorton #1 will vent 1.4 CFM at 2 ounces. Gorton #2 will vent about 5.5 CFM at 2 ounces.

I have about 70 feet of 2&1/2" in ea. main, about 2.1 cubic feet of air. I used two #1's and they work well.

From an email from Gorton:

#1 - 4.08 CFM at 1 lb.
#2 - 16.32 CFM at 1 lb.

Bottom line: Measure the volume of your mains.

Steamhead (in transit)

That blast from the past

has been superseded by the Gerry Gill/Steve Pajek venting charts. Not gonna steal their thunder by posting the actual venting rates they measured as opposed to those we calculated and interpolated all those years ago. If you want to see their measurement results, get a copy on the Books and More page of this site. It's in the form of an Adobe e-book, and all proceeds go to charity.

Bob W._3

If you have large rads, the C and D model Gortons work well. the D model vents the same as the #1 I believe, subject, of course, to the inherent limitations of the 1/8" thread.

Steamhead (in transit)

Actually

assuming you started timing the steam distribution thru the mains from the point at which the boiler started generating steam (after the few minutes it took to bring the water to a boil) they're still slower than they should be. You want the steam to fill the mains in about a minute.

Try installing two Gorton #1 vents on each main. Pipe a tee on the vent riser with the run vertical and a street ell in the bull, pointing up. Then install your vents.

Jim Franklin_2

Main vents maybe not the problem

I removed the vents altogether and it took 7 mins to get steam from header to one of the ends, so I think there's something more basic that's the problem. I have about 80% of the mains insulated. It takes almost 3 minutes just to get steam from the beginning of the risers into the header, which seems excessive. I've attached a drawing of the near boiler piping. Can you have a look and tell me if the lack of a riser on the rear tapping is causing slow steam flow? The two tappings are joined with a union, i.e. there are no swing joints, which has me concerned as well...

thanks,
jim

Steamhead (in transit)

Uh-oh

If the steam is not going into the mains, you may have a leak above the waterline of the boiler. With the boiler OFF and COOL, open the fill valve and fill the boiler past the top of the sight glass until water reaches the risers. If water runs into the firebox or on the floor, you've found the leak.

If you don't have a leak, you can look at correcting that badly installed near-boiler piping. Go to the Library page of this site and look at the "Steam Piping" category for "Drop Headers". From your drawing it looks like your boiler needs two risers to the header so a drop header would be a fine choice.