Header size/velocity question

Clance

Hi Folks.
SO I happened upon the velocity chart below on this forum. I am having installed on Thursday a Burnaham MegaSteam MST288 on my single pipe system.

The chart says that using two 2" risers cuts the velocity from 30.6 to 15.3...pretty straight forward. But then is says that using their recommended 2" header has a velocity of 30.6 and going up to a 3" header cuts the velocity to 13.9. Which also makes sense.

If I remember correctly, Dan in Art of Steam recommended trying to stay under a velocity of 15.

So would I would be better off to forget Burnham's recommendation for 2" header and go for a 3" header instead? I don't know if it matters but the mains on my systems are a 2" and two 1.5",

Is my interpretation of this chart correct that a 2" header off two 2" risers increases the velocity from 15 back up to 30 and sort of negates the slowing of velocity that is being accomplished by using the 2 headers ? What am I missing?
Thanks! Rick

Jamie Hall

Use the two 2 inch risers -- but also use at least a 3 inch header. Anything smaller for the header and the velocity in it will go back up, of course, once both risers are feeding it -- and that you do not want.

ethicalpaul

I would respectfully disagree a bit with @Jamie Hall here.

If you use two supplies, the velocity will be nice and low at a most critical area--the area where water can get carried to the header in the first place. This is a definite benefit regardless of the header size.

If there is no or little water getting carried to the header (and based on my observations there won't be), it doesn't matter if the velocity increases again in the header.

It won't hurt a bit to have a larger header, but in my opinion it won't help you.

See my video on this topic here: https://www.youtube.com/watch?v=4IymyZB4wlI

Jamie Hall

I'd agree that it's debatable, @ethicalpaul . The main thing really is keeping the velocity down in the risers -- as your lovely demonstration video shows! I suspect that the actual layout geometry has as much to do with keeping water out of the mains as anything else, assuming the riser velocities themselves are low enough.

And, of course, there is the minor (?) detail that not everyone is equipped to thread 3 inch pipe...

ethicalpaul

On the bright side, if one does want to use 2.5 or 3 pipe for the header, it is really just short nipples that are used so it's very doable even without a threader (I almost did it myself but those fittings are very pricey and even I couldn't justify it )

EBEBRATT-Ed

Keeping the water in the boiler and out of the header is a good first step.

I haven't herd of a boiler that was piped correctly using the MFG minimum spec not work. I know the header is supposed to separate the water and the steam but why let the water out of the boiler

Clance

@Jamie Hall
@ethicalpaul
@EBEBRATT-Ed
Thanks for all your help!! That info was just what I was looking for. I had to commit the the supplies for tomorrows MegaSteam 288 install before anyone posted -and the fitter doing the install tomorrow said 2" dropped header- so that's the decision.. But I am having the 2nd MegaSteam 288 installed in a couple weeks, so great info to know.
Your opinions and explanations of how really the most important factor is the risers slowing the velocity directly out of the boil certainly assuaged any concerns that a 2" header may be too small.
- and @ethicalpaul - great video!
You're all very kind to take the time to share your knowledge and you make this site a traffic resource.
So - A huge Thanks again for all your help!
Rick

AdmiralYoda

So what you guys are saying is that my plans for dual 2", 24" long risers (above the top of the boiler) with a 12" horizontal run to a 6" drop into a 3" header is overkill?

Throws off my whole spring boiler re-pipe plans.

EBEBRATT-Ed

@AdmiralYoda

If you ask 10 people on this site you will get 10 different ways to pipe a boiler and in the end all will work

We see so many horror stories here of installers who can't read or won't read the install manual that just seeing a job installed in accordance with the MFG minimum piping requirements is a joy to see,

In @Clance 's job above I believe he has a good contractor who knows what he's doing. He's using 2 risers and is exceeding the MFG requirements by putting in a drop header.

I have never seen a boiler installed to the MFG minimum that didn't work.

Others on this site have different opinions to which they are entitled. The like large headers and drop headers. I have no objection to any of that. They do that because of their experience and their comfort level with different boilers

There is no right or wrong answer as long as it meets the mfg minimum

JohnNY

My brain stopped working and I'm writing a report for a client. How do I get to "pounds per hour" from BTUs or EDR?

EBEBRATT-Ed

1000 btus in a LB of steam

A pound of steam is a pound of condensate

A gallon of water is 8.33lbs

1000 btus/lb of steam/240 btus/EDR= 4.166 EDR/lb of steam

JohnNY

@EBEBRATT-Ed Thank you!

STEAM DOCTOR

Is there a chart somewhere about the affect of boiler riser hight? Something about the max height that water can climb at various steam velocity.  Seem to remember such a chart in Lost Art. Thanks 

EBEBRATT-Ed

@STEAM DOCTOR

Page 74ish in LAOSH...Revisited

Talks about if the riser is kept below 15fps the water will stay in the boiler and not go up the riser. I didn't see anything on riser length but I only looked quickly

STEAM DOCTOR

EBEBRATT-Ed said:

@STEAM DOCTOR Page 74ish in LAOSH...Revisited Talks about if the riser is kept below 15fps the water will stay in the boiler and not go up the riser. I didn't see anything on riser length but I only looked quickly

Thanks. I know about the 15 fps. I have in my head that water will only climb a certain hight at certain velocity. Maybe @The Steam Whisperer (Formerly Boilerpro) posted something?

SteamingatMohawk

Being a consistent PIA about this stuff, here's the full skinny, from Lost Art, P. 74-75, not my imagination.
Dan's data on Old boilers 12 - 17 fps, Modern boilers 25 - 36 fps.

Dan Houlihan's opinion (if that's the right term) is no more than 25fps. That's how I built my chart.

The 15 fps is from a long ago guy named Ara Marcus Daniels in the days of old boilers.

An interesting side comment is that 2 @ 2" tappings have 2 x 3.36 sq " = 6.72 sq " and 1 @ 3" is 7.39 sq ", so the 3" pipe can handle both at less velocity.

As I mentioned in a different discussion, a short length of the same size probably doesn't make much difference and I expect the manufacturers are not going to try to force multiple sizes on the installers, even if it does affect steam velocity.