Pipe size vs double header

2" out of the boiler vs 4" out of the boiler. the boiler ports are still 2 inches which means velocity will be faster with only one port. You have a venturi to deal with.

You get slower, drier steam velocity using both ports -economically.

A single 3" has more surface area than two 2" but two 2" may pull more evenly. This is assuming the boiler has 3" tappings.

Going up a size out of a tapping is a huge no no in my book because you're dropping velocity and there's no where for water that's already been sucked out to go, meaning it'll tend to get trapped in that riser. The slower steam will tend to not want to pull it up as well as higher velocity.


Going down a size after you leave the tapping could be beneficial and certainly won't hurt. But never go up a size.

Snowmelt said:

Ok so on the riser you don’t increase the size but you will increase it at the header ?

Just so. Remember that the idea is to let the steam slow down somewhere where the water droplets can drop out and make their way, unimpeded, back to the equalizer and the back to the boiler. If you increase the riser size, they'll drop out in the riser, and try to get back to the boiler that way, which isn't helpful. But if you increase at the header, and the header is piped riser/second riser if any/steam main(s)/equalizer, they'll happily drop out in the header, miss the corner up to the steam main or mains, and go back down the equalizer.

I don't agree. I have no problem blowing up the riser size.

The job of the boiler is to be a steam boiler and keeping the water in the boiler is the deal. It's job isn't to circulate water through the header

It makes no sense to me to allow the water to blow up into the header and recirculate back to the boiler

the riser size is supposed to keep water in the boiler and a bigger riser will help make that happen. 2 risers are better than 1 riser blown up. The more time the water is in contact with the steam the more the water will condense some of the steam

EBEBRATT-Ed said:

I don't agree. I have no problem blowing up the riser size. The job of the boiler is to be a steam boiler and keeping the water in the boiler is the deal. It's job isn't to circulate water through the header It makes no sense to me to allow the water to blow up into the header and recirculate back to the boiler the riser size is supposed to keep water in the boiler and a bigger riser will help make that happen. 2 risers are better than 1 riser blown up. The more time the water is in contact with the steam the more the water will condense some of the steam

Im assuming you are misunderstanding what I said.
I was talking about using a larger size riser than the tappings.  For example a 3" on a boiler that only has 2" tappings.

So it'll go from 2" to 3" after it's already left the boiler.

Danny Scully said:

The tapping on the boiler sets the velocity, increasing it after that does not slow it down...so ultimately I’m agreeing with you @ChrisJ, but for a different reason. I just think it’s a waste. 

You don't feel the velocity drops once it gets to the larger piping? Isn't this how and why venturis work?

Interesting discussion. Viewpoints on all sides here! Seems to me, though, that the main thing to remember is that where the steam slows down -- and it will if the pipe size is increased -- water droplets will form. Can't avoid it -- it's one of the oddities of saturated steam, even if you don't have some carryover -- and the objective of the exercise is to avoid getting those water droplets into the steam mains, but letting them go somewhere (like the equalizer) where they aren't a problem. Whatever works...

The advantage, as I see it, to two risers in longer boilers is that it avoids potential problems with tilting waterlines, as well as lower velocities, and therefore less potential for entrainment and carryover. Are they needed? Not always. Cedric -- a 5 section Weil-McClain 80 -- only uses one riser and is fine, but of course it also has a generous dropped header -- and a big steam drum after that. Odd... Boilers with side outlets... from the standpoint of the hydrodynamics of the thing, pipe as generously as possible!

Here's a video showing how water gets sucked up into the piping of a boiler.

Yes, it's high pressure and a commerical boiler but the idea is the same

https://youtu.be/dorhr85ASRM

@ChrisJ is right on all counts. I would like to believe the boiler manufacturers considered everything before they decided on tapping size and quantity.

You've got the all important "A" dimiension, steam pressure less than, equalto 2psi and finally installation costs. The larger the pipe, the more expensive the install, not to mention the added difficulty of threading and sizing larger pipe.

Putting 4" risers on a residential boiler is like putting a V12 in a volvo 240. It is cool, but it is expensive.

Required riser size depends on the boiler output.  Just as with boilers and air conditioners bigger isn't always better.

They should be sized appropriately.  Doing more than a 2" header on an EG30 is a waste in my opinion.

An EG40-45 a 3" is nice.