Pipe size vs double header

Snowmelt

On your riser going into your header vs using both risers.........
For sake of arguments a smaller residential of 100,000 btu
I know that you guys are going to say use both headers all the time and increase pipe size.
But what would be better if you just increased pipe size and use one header or keep minimum recommended size and use 2 risers & why?
Follow up question goes it matter how many risers are on original main?

SlamDunk

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.

Snowmelt

Thanks slam that’s a short and right to the point.

ChrisJ

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

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

Jamie Hall

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.

Snowmelt

Ok Jamie thanks, so don’t increase risers but increase the header.

EBEBRATT-Ed

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

Snowmelt

I wish dan would chime in on this .......

ChrisJ

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

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. 

Snowmelt

Dan would you oversize anywhere in the system?

Danny Scully

@Snowmelt, there is a formula for header sizing that I always use. Many times we upsize the header against the manufacturers specifications. In terms of the entire system, in counterflow situations we will upsize, as well as longer run-out (counterflow) situations.  

ChrisJ

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?

EBEBRATT-Ed

Say a 2" tapping with a 2 1/2" riser. I don't feel the velocity in the 2 1/2" riser will be the same as a 2" riser. The velocity will slow as soon as it passes through the tapping. Plus the tapping is only what? an 1 1/2-2" Its not even going to have time to speed up much

Jamie Hall

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!

ChrisJ

Gentlemen,

The only thing that matters as far as pulling water of a steam boiler is the diameter of the opening of the boiler and it's distance from the water and the amount of steam you're pushing through it.

  It doesn't matter if it's 1 foot thick or 0.0001" thick the velocity is what it is at that spot.

The gas doesn't need time to accelerate.   When you force X amount through a certain size opening it must go a certain speed.

Sigh..

ChrisJ

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

unclejohn

I have never installed a steam boiler but it would seem to me that lower velocity would mean less water leaving the boiler.

SlamDunk

@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.

Snowmelt

I only did a hand full of boilers, I never had to cut pipe. I did have a lot of nipples that I had to bring to supply house but I do have my standard nipple tray.
At the end of this conversation I am believing 2 risers are better then one. Bigger is better (2 inch to 2 1/2 or 3) drop header is even better for the steam. And if the header is a even a bigger barrel it will slow down the steam even more.

ChrisJ

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.

Snowmelt

I’d keep that in mine.

DanHolohan

I would use two risers of the size specified by the boiler manufacturer and the go larger on the header.