Main vent question

moneypitfeeder

Okay, here's the short question. Should I add more main venting? The scenario is a properly piped boiler, 2 pipe vapor system. 2 mains, each with 1 Gorton no.2 at the end of the main, on an antler. I sized the vent capacity using standard charts with steam at 2 psi, but I am operating at about .2 psi. The vents are "breathing" during startup. (During Dan's seminar, he stated that if you can hear a vent it is not venting enough, and I'm not sure if that only pertains to radiator vents) . The breathing sounds kinda like venting, and a slight almost whistle. I'm wondering if because steam likes to fly at lower psi's, then I need more than "normal" venting to facilitate that. My mains are 2" blk iron, 1 @ 40ft, second @ 35ft.  If anyone has links to charts that I could figure out the vent rate that'd be great too.Thanks, Dee

Dave in QCA

which chart?

What chart did you use?

moneypitfeeder

now your asking me to dig

Okay, that was months ago, and with our house flooding, I'm not entirely certain I can find where I put that reference. Give me a few and I'll try and locate it.

moneypitfeeder

Lord only knows

Maybe I'm remembering measuring something else at this point. I can't find the reference that I thought I was basing everything off of. I just re read "Greening Steam" and I think I've answered my question, yes I need more venting.

nicholas bonham-carter

what pressure?

if it is a vapor system, it will operate much better at a pressure much lower than 2 psi. do you have a good low-pressure gauge? a vaporstat would also be helpful here.

with such a gauge, you can see from the back-pressure during venting whether the existing vents are allowing the air out without excessive restriction

now that your piping is top notch, why not get the pressure right? why pay for extra fuel above a few ounces?--nbc

moneypitfeeder

I'm operating at

0.1 to 0.2 psi and yes I have a vaporstat and a wika low pressure gauge in addition to the 30 psi required guage. Thanks, Dee

nicholas bonham-carter

Heavy breathing

Have you checked the slope ahead of the vents for a sag which may be trapping condensate and allowing it to interfere with the flow of air out of the system?--nbc

crash2009

Venting chart

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



Is this the chart you are looking for?

Jamie Hall

More vents

never hurt anybody, Dee -- but the question is, are they necessary?  (and yes, I have spent my whole life questioning received wisdom -- kjust my nature, I guess!).  I would honestly say that if your system is holding down around 0.2 psi or less when it's running, you're fine.  To give you an idea -- the building I super has about 150 feet all told of mainly 2 1/2" to 3" steam mains, and is vented by one Gorton #2 and one Hoffman #75.  I don't have a low pressure gauge, but I do have a vapourstat of the lovely old mercury sort which one can actually see, and the pressure just barely lifts the diaphragm off the "zero" peg when it's running (the system is set for a 6 ounce cutout, 1 ounce cutin) so it's running around 2 ounces.



Charles is always after me to add more vents... but it don't seem broke, so I don't aim to fix it!

Dave in QCA

Vents are satisfactory

First, an excess of vents on the mains cannot cause a problem.  However, you will have a higher chance of a failed vent and more money invested that is not doing anything.

Using the charts in Greening Steam I find that 2" pipe has .023 cu ft per linear foot of pipe.  You have mains that are 35 and 40 feet long.  Let's use the 40 foot main for calculations.  .023 cu ft / ft X 40 ft = 0.92 cu ft.  

The general convention is that 3 minutes is an acceptable time for the steam to get to the end of the main.   So you need a vent that will let air pass at,      0.92 cu ft / 3 minutes = 0.307 cu ft / minute (cfm)

Your Gorton #2 will vent at the rate of 1.1 cfm at 1 oz of pressure and 1.75 cfm at 2 oz of pressure, and 2.2 cfm at 3 oz.

It sounds like you're pressure once the boiler begins to steam is running 2 to 3 oz.   You should be just fine with one Gorton #2.  You have way more than enough venting.



From my own observations, my Gorton vents close slowly as the steam approaches.  As they are closing, they do sometimes make a hissing sound and I have noticed that this can last a while.  The closing temperature on the Gorton is well below that of steam, as I recall, it is around 180F.  My Gortons begin to close and then they hiss a bit.  Even though the body of the vent is warm, it is certainly not the temperature to steam.  They continue to vent very slowly for quite a while.  More hiss than anything.  Never any steam escaping.

moneypitfeeder

the slope is good

They are located at the end of a antler, and the slope pitches back to the main (then drops directly to a wet return.) 

moneypitfeeder

well

That wasn't the one, but that is one I intend on picking up. Thanks

moneypitfeeder

I hear ya

I definately subscribe in every other aspect of life, that if it ain't broke...but darn it I've become obsessed with trying to squeek out the most efficiency out of this system.

moneypitfeeder

thanks for the insight into hissing

This might seem like a really silly question, but how do you start your timing to measure how long it takes for steam to get to the end of mains? The low pressure gauge doesn't register but a flicker when the main vents close, so the only way I've been able to time things is from a cold start it takes 12-13 min for the vents to start hising (that's also when the main pipe in that location starts getting hot. Then it takes a few more minutes to close them.

Dave in QCA

several things to look at

I can tell when my boiler starts to steam by a few things.  The sound of the boiler when it boils is a bit different then when it is simmering and coming up to a boil.

Also, I can put my hand on a bare spot on the piping coming out of the boiler.

Also, my gauge is a 32 oz model.  The first increment is one ounce, and it raises to one ounce shortly after the boiling starts.



If your Gorton does not start to make hissing sounds until the steam is very near to it, you know it is happening because the vent is beginning to close down.

Patrick_North

What takes 12 minutes?

I've been following this thread and I'm definitely missing something. If you mean that in about 12 minutes you can go from cold boiler water to having steam at the ends of your mains, then I'd say bravo. Are you running oil, natural gas, or uranium? I'm jealous!

However, if you mean that it's taking 12 minutes after the boiler makes steam to get steam to the ends of your mains, I think you can do better. The method Dave mentioned is the one I use. The pipe will turn from "hey, that's nice and toasty" to "can't hold my hand there more than a second" quite sharply. Also, if you've got a beefy header it's even more accurate to measure from the takeoffs from the header, not the boiler. My layout is a bit larger than yours (about 100' of 2" split over two mains) and I get all the air out of 'em in under 5 minutes from a cold start. Probably a bit better now that I've re-insulated. I'm using three Gorton #2s on each main.  I get no hissing at any point. My radiator vents - which always seemed quiet enough to me- are also noticeably quieter (read: utterly silent). If you haven't yet read the Gill/Pajek venting pamphlet, I'd recommend it.

The low pressure is a good sign, but that doesn't mean you couldn't evacuate those mains quicker. That  = shorter burner run times, and that = lower fuel bills. With a clearer sense of how long it's really taking to push the air out of your mains AND how adding more vents will affect this time (something the venting pamphlet helps you understand) you can make some educated choices about ROI, etc.

Good luck!

Patrick

Jamie Hall

I think Dee means

from a cold start, cold boiler.  That's about what mine takes too...

Patrick_North

Hmmm...

This feels like one of those occasions where I become "aware of being unaware." I'll start a new thread so as not to highjack this one.

Thanks!

Patrick