Can the supply take-offs and header be oversize?

Tradecraft

<span>I am installing a Peerless 211A-8 at an altitude of 5000 feet.  The sea level output of the boiler is 1,176,000 btus.  The boiler has 6" steam tapings and Peerless recommends that two 5" take-offs supply a 6" header.  Using this recommendation I calculate the velocity of the steam in the 5" take-offs to be 23.53 ft/sec (the velocity in each 5" pipe).  It is my understanding that the closer you get to 15 ft/sec the better.  If I upsize the two take-offs to a full 6", supplying a 6" header, I can get the steam velocity down to 16.28 ft/sec (the velocity in each 6" take-off).  Should I stick with the recommended two 5" take-offs to a 6" header and live with the higher velocity or should I upsize the take-offs to 6" to try and bring the velocity down?  Is the any downside or error piping everything from the boiler to the header in 6" in any event?  I am trying to ensure that I keep the steam as dry as possible.</span>

clammy

velocity formula

when using both riser on  the boiler fiqure that into your equation because that will be the real  boiler exiting velocity not what a single riser will be ,when doing the math add those 2 inside pipe  tranverses not just one .What are the size of your system mains and don,t undersize your equilizer do it in 3 inch and try a drop header for your header life and conneting those riser will be easier at below 15 fps on your exiting velocity will be suppling some dry steam and your system will love you peace and good luck  clammy  PS have you looked at a 2 stage burner for that puppy i know it will be weeks off in the making thats why i used a LC model on the one i am working on luckly got a beckett cg50 for it   good luck bro

Tradecraft

Velocity provided was calculated for each take-off

The velocities were calculated taking into account the two take-offs, splitting the total velocity between the two pipes.

 

The header will supply one 4” main and one 3-1/2” main.  Peerless specifies a single 2-1/2 equalizer and I was planning on piping it as 2-1/2”.

Long Beach Ed

My feelings...

... are that the two 5" risers should be sufficient.  Especially if a drop header is used. 



Of course six inch risers would be better. 



The success of your design depends greatly on the system and how tolerant it is to wet steam.  I believe that by following the manufacturer's specifications, the system will work well unless some other factor, like bad pitch, undersized pipes elsewhere call for dryer conditions.



On a job like this I would install a drop header.  It will make the piping easier, provide ample swing for thermal expansion of the pipe and help dry the steam.



If you are welding that beast remember to leave enough pipe on those risers to allow for that expansion, else you'll have leaks down the road. 

Tradecraft

What are the risks and downsides to going with larger than recommended take-offs?

What are the risks and downsides to going with larger than recommended take-offs?  (Using two 6" take-offs supplying a 6" header v. the recommended two 5" take-offs supplying a 6" header.)  If I use 6" take-offs rather than 5" should I up-size the equalizer, or since the header will remain the same 6" keep the equalizer at the recommended 2-1/2"?

jpf321

I believe...

generally bigger near boiler piping is always better. remember that originally boilers had huge steam chests and that these days the piping makes up for the loss of cavernous chests.

nicholas bonham-carter

5 inch, or six inch, that is the question

6 in. fittings could be more difficult to obtain than 5 in. could that be a problem? in addition, the length of the larger fittings could make for a challenge. i wish we had known of the drop-header concept when we did ths; but we just followed peerless' instructions, in the manual.

my 211a with 1,050,000 btu's seems happy with the 1  5 in. riser as specified in the manual, as i have the v-stat set for 2-8 ounces. if you use the larger size, then best to add some more main venting, as the steam chest is full of air, as well as the pipes at startup.

are you using the "mod-u-pack" hi-lo-hi burner setup on this one?--nbc

Tradecraft

Fitting availabilty is not an issue...

We can get 5 or 6 inch fittings, so that is not an issue.  Also, we have plenty of ceiling height, so we can easily get 24" between the top of the boiler and the bottom of the header (which is about 34" above the water line) so I don't think we need a drop header to help dry the steam.

The issue is that two 5" risers (or take-offs) from the boiler will cause the steam to exit our 211A-8 at 23.53 ft/sec.  This is much higher than the preferred 15 ft/sec.  If we up-size the risers from the boiler to the header to 6" (essentially 6" swing-arms) we can lower the steam velocity to 16.28 ft/sec.  The lower velocity is preferable, but at what consequence?  Is there a problem with having the risers and the header the same size (6")?  Is there a reason you would always want the risers to be smaller than the header? (Aside from availability and cost.)

If there is no performance or functional downside to piping the two risers feeding the 6" header with 6" pipe as well, why would I not want to use 6" all the way from the boiler through the header? (I will be supplying two mains: a 4" and 3-1/2").  Alternatively, is there any reason to use 5" risers rather than  6" risers, serving a 6" header?  (Peerless always specifies risers that are smaller than the header for any given boiler size.)

RE the gas train: we originally specified a mod-u-pack, but several sources discounted its actual efficiency (strongly stating that on/off modulation was just as good as high/low).  We were even told it may be discontinued.

jpf321

the only downside...

that I can think of would be more heat loss from larger pipes. thus requiring better insulation. and perhaps pickup factor consideration, friction loss, more surface area for condensing/bringing to steam temperature. the upside being drier steam and, slower velocity.



maybe a pro can verify my thoughts

The Steam Whisperer (Formerly Boilerpro)

Do it....

The bigger the risers the better.  If you can get the velocity that low in your boiler risers, you will have nearly completely dry steam even before you get to the header.  I have several boilers that the risers are big enough that they remain below critical velocity and work great. 





Use only threaded fittings for the elbows on the drop header.... they need to be able to move to compensate for the different expansions rates of the steel header and the cast iron block of the boiler.   The rest can be welded if you chose.  In other words, follow Peerless's directions and don't do like the photo below.





The only downside is that if you use any kind of electronic low water cutoff in the equalizer, it usually won't work because the water coming down the equalizer is nearly pure steam condensate, which means it contains no minerals.  Pure water does not conduct electricity and the electronic probe cannot sense the presense of water.

Tradecraft

This is what Peerless Boiler has to say on the matter

I spoke with Peerless Boiler and they indicated that the sizes specified in the manual for boiler take-offs and header sizes are the MINIMUM recommended sizes.  You are free to use larger sizes if other design considerations motivate you to do so.  In no event should you use sizes smaller than those recommended in the installation docs.



In our case, we agree with the post from Boilerpro (David Bunnell) and will be installing the boiler take-offs and header with 6" pipe and fittings; paying special attention to use threaded elbows on the swing-arm joints (see attached).



Thank you everyone for you input and advice.