steam header size please

GW

I lost my Lost book- I am looking at a job with a sq. ft steam of 1796, the boiler has two 3"ers for the supply. What size header might I want for this beast? Do you guys often weld ( I'm not out to lunch, obviously I'll swing some 90s here ) into a header this big? Thanks for the help!

Gary Wilson

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Boilerpro_3

I'm guessing you don't have factory manual

What brand, gross output and model do you have? Different boilers have different requirements.

As a general requirement, The area of the main steam cross header should be equal to or larger than the total areas of the Steam supply mains leading from the header (Dunkirk D-247 manual) I believe older recommendations are for 50% greater than this sum.
Also leave space between the last supply tapping connection and the first system take off to allow the header to do its work. A minimum dimension of 15 inches is given for smaller 2 1/2 inch headers, I'd bump this up some (maybe 30 inches) for a 4 inch header. This also depends on header size versus steam load. Also leave some space between the take offs to allow the water to settle back to the bottom of the header. Most of this wisdom came from Noel at Slant Fin and the Dunkirk manuals.

Something like this, only lots bigger.

gerry gill

i would use a 4'' header..

but then i always use a 4'' header....tho the instructions may call out for a header thats equal in cross sectional area to the square inches of all the takeoffs.

Alan(CaliforniaRadiant)Forbes

So

2 headers x 7.07 square inches (area of 3" pipe) = 14.14 square inches

The diameter of 4" pipe is 12.57 square inches; that means you would have to use a 5" header, but gerry seems to have enough experience to be comfortable with 4" pipe.

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GW

header

correct- I do not have the manual- just pricing up a job. I suppose I can see if Smith has the install manual. It's a 19-5 boiler. Thanks!

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Steamhead

I was going to suggest that

Go straight to the source- I've had real good luck, many manufacturers still have the old stuff in their dusty file cabinets.

Remember that the pipe sizes, riser heights etc. that they give are minimums in many cases. There's nothing wrong with using a 3" header, for example, where they call for 2-1/2" or substituting 4" for 3"- especially on Vapor systems. But don't go smaller than specified, or you'll have big problems.

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Boilerpro_3

It's the area of the system supplies

not the boiler supplies that you must equal. I expect that this helped be sure that a header would be "oversized" for vapor systems since the mains would be larger than is typical for regular steam systems.

Boilerpro

patrick linhardt

steam velocity in header

I like to look at the manufacturer's recommendations, and also the velocity of the steam. I agree with steamhead in that oversizing is OK, in fact in many cases prefered. The goal is to produce the driest steam possible. The old time manufacturers did this with huge steam chests and lots of large supply outlets. They would have leaving velocities of as little as 10 fps. They wanted to leave all the water in the boiler. Checking our modern boiler recommendations, we can find velocities as high as 50-60 fps. This kind of velocity is close to getting you in trouble.
Your two 3" risers are going to have a leaving velocity of around 35 fps, which is OK. Your 4" header will be around 42 fps. Using a 5" header will get you down to 26 fps, almost 40% slower. If you can, or need to, slow the flow for better water separation and drier steam. The system will heat better and the energy bills will be lower.