timing the main venting

GW

Steam people, Just so I'm clear, I presume a cold main heat slower than a hot main. So when i time the old venting, do i heat up the main all the way, then shut if off for 5 minutes or so, then time it? Then add some venting, and repeat?

It would take forever to time a 'cold main' with old venting, then compare that with a cold main with new venting, just for sake of comparison. (I like to compare, but maybe a waste of one's time)

Or, maybe I'm way over thing it.

Thanks

ethicalpaul

Yes. Do a normal call for heat, see steam close the existing vent, then shut it down, remove the vent, and fire it up again.

Then time how long before steam starts coming out of the vent supply nipple. That's your "vent-free time".

Then put on a new vent and do it again. If the time is significantly longer than the "vent-free time" then you need more venting.

You are right, it's a waste to time the "main vent close time from cold startup" because you want to have enough venting to handle the warm startup, and you know the cold startup will require less venting so there's no need to bother with that.

GW

Paul good, my Hoffman Diff loop customer wants a bigger vent and some trap cages, time to get busy and make some quick timing records and maybe extrapolate some fuel

EBEBRATT-Ed

@ethicalpaul

I think your post is spot on except for one thing I don't get is "you know the cold startup will require less venting"

What am I missing?

mattmia2

Since the steam will condense as it heats the cold pipe, it will progress slowly as it heats the pipe anyhow so it is pushing less air in front of it than if it is progressing through a relatively hot pipe. It won't progress beyond a given point until it has heated the pipe to more or less steam temp at that point.

ethicalpaul

Yep that’s what I was thinking @mattmia2 🙂

mygardenshed

mattmia2 said:

Since the steam will condense as it heats the cold pipe, it will progress slowly as it heats the pipe anyhow so it is pushing less air in front of it than if it is progressing through a relatively hot pipe. It won't progress beyond a given point until it has heated the pipe to more or less steam temp at that point.

So an insulated and well vented mason is most effective during cold days where there will be more calls for heat? As opposed to a day where you only get a call for heat two or three times per day?

mattmia2

Yes. It is more effective from a cold start too, the main will take less heat to get from cold up to steam temp if it is insulated as well.

EBEBRATT-Ed

@ethicalpaul @mattmia2

So the total amount of air the vent must pass is the same but it vents at a slower rate.

I'll buy that, thanks

mattmia2

At least that is what we think. You've forgotten more than we'll ever know @EBEBRATT-Ed

GW

okok so heat up the main then do the 'testing' so all the numbers can be 'close to being accurate'??

Jamie Hall

I take a somewhat different approach, @GW , but it is, I think, much more suited to two pipe systems with crossover traps than to one pipe systems or two pipe with end of the main traps.

It's based on the supposition that the crossover traps have greater capacity than any main vents except the very very biggest ones, and that all the venting is in one place, where all the dry returns connect before dropping to the boiler. In such systems, the guide I use is pressure, based on noting that there really are only two sources of pressure drop: friction loss in the mains and dry returns and the vents themselves. Then, if the vents are adequate for the job, the primary loss will be in the piping, and that is constant. So, if you watch the pressure (either cold start or warm start) what one sees is that the pressure rises as soon as steam starts to be made, but to a very low value -- which will be the friction loss in the piping. If it stays that low, or rises only very slowly, clearly the main vents are not restricting the flow any more than the piping is, so you have enough venting. On the other hand, if the pressure keeps rising, it has to be the main vents restricting -- so you need more main venting.

Which makes sense to me, but not, perhaps, to anyone else! The result of which is, however, that Cedric, the largest system I play with, has what seems to be absurdly small main venting considering that there are about 200 feet of 2 1/2 and 3 inch main: the main vents are an elderly Hoffman #75 and a Gorton #2. One each.

ethicalpaul

Yeah sorry I should have indicated my test is for one pipe steam. I'm too ignorant of 2 pipe systems to have an opinion.

GW

Jamie that seems logical. Rising needle means the bag is getting pressurized (I like the “filling the bag” analogy)😀

EBEBRATT-Ed

@mattmia2

Many on here that know more than I do. In my years on the job I did a lot of different things (to many) but didn't master any of them. It kept me employed....that's about it

GW

I’ll also get a 3lb gg installed and watch the needle as I time the venting 

GW

Still trying to get my White Belt in two pipe😀. The crossovers, I didn’t stick my camera up there to see the make model, but in general, it’s pretty basic to update these with new traps? Bigmouth? Big wrenches ??? 

Seems like I might has to fuss with the spud a bit. I’ll need to cut into that coupling? 

Jamie Hall

That's probably a plain vanilla radiator trap -- whatever they were using. I'd be mightily surprised if Tunstall or Barnes & Jones didn't have replacement elements for them. Have you checked them? The steam main should heat quickly, and the inlet pipe to the trap should be good and hot, and the outlet should be much cooler.

JUGHNE

That looks like a Merchant coupling with no taper.
If so there are only 2-3 threads that actually tighten.
It might unscrew fairly easy.

IIWM, I would unscrew the union nut and get the coupling to unscrew a little.

Then cut the spud off so the trap could easily unscrew.

Just another 10 minute job.

GW

Jamie there are two mains, two traps, I will check it out. One side of the house is trouble free, the other side has concerns
Just trying to spend the guy's money once instead of twice, if at all possible.
Thanks

GW

J ok cool, I'm decent with a sawzall, band saw, what have you.

Steamhead

That's a Hoffman #18 crossover trap. It's rather slow in that application. We replace these with Big Mouth traps all the time, and use Gorton #2 vents at the Differential Loop.

Are both mains the same length and diameter?

GW

Yes, they seem very close in length 

Steamhead

OK- I'd use a Big Mouth 1/2" crossover on each.

GW

Thanks Frank 

GW

I know you’re not supposed to line size f and t, but can I do 3:4” big mouth? 

Jamie Hall

You can, @GW -- but I think it's overkill...

Oh -- and I hope you are talking about Big Mouth traps, not vents? You don't want vents there on that system.

GW

Jamie yes it morphed into a crossover conversation 

JUGHNE

Are B&J Big Mouth air vents and cross over traps the same thing?
I recall the discussion here of the development of the BM just a few years ago,
IIRC it consisted of their large traps.

They both pass air and then stop steam.....and occasionally spit a little water.

EBEBRATT-Ed

@JUGHNE

Yes. On the B & J website it's listed as "big mouth vent & crossover trap"

GW

I got the impression they are not to be used as radar traps, they don’t deal with water

neilc

radar or klinger ?

Jamie Hall

GW said:

I got the impression they are not to be used as radar traps, they don’t deal with water

The aren't, or shouldn't be. They don't have any way to close or open for condensate. They can be used as crossover traps, though, since the outlet is threaded.

Steamhead

GW said:

I know you’re not supposed to line size f and t, but can I do 3:4” big mouth? 

If the existing crossover traps are 3/4", use 3/4" Big Mouths to replace them. If they're 1/2" as I think all Hoffman #18 traps are, use 1/2" Big Mouth crossovers. This keeps the piping simple.

JUGHNE

The B&J BM are available in 1/2" also at Supplyhouse.com.

GW

Ah ok sadly I didn’t note the size of the pipe. I’ll make another trip over there and gather more data. Jamie showed me his two pipe Hoffman today so I’m feeling more equipped 😀 maybe the system will work better with a Vaporstat. Maybe the Hoff Diff Loop is shutting things down. Gotta throw a 3 psi gg on and see what’s up and feel some steel (dry returns)

thanks @Jamie Hall for the tour and the history, the world is changing quickly and it’s good to soak up some old stuff once in a while. Tomorrow’s generation will have some issues, I suspect 

Jamie Hall

You're welcome, @GW ! That was a very pleasant afternoon, and I hope you picked up something useful along the way (besides being kind about a somewhat odd basement...).

GW

I went back- the old 77 vent was in very sad shape. I was still hissing 10 minutes after the boiler shut shown,

I heated thing up and timed things. One main is fast, one is slow, so a new crossover is in order,

Frank, the Big Mouth--does one change the spud or does that bolt up well? Yes it was 1/2", seems to be the same Hoffman as the rad traps. Just wondering if it's a 30 min job or 15 minute job.

GW

the big mouth- I have one here and I measured the Hoffman. The BM seems 'less tall' and it's 'wider'
I can always bring the hand threader and re-nip the 1/2"

GW

I would like my white-belt ceremony for two pipe Kung Fu, thank you 😊 

EBEBRATT-Ed

Looks like it fit. Did it work?