System riser between two boiler risers

Bill_110

The installation manual for my boiler says system takeoffs must never be between two (boiler) risers. If one used this configuration (of having a system takeoff between two boiler risers) what would be the likely downsides? Would there ever be a situation, like in dealing with space constraints, where you might put a system takeoff between two boiler risers, and could you do other things to compensate for the negative effects? Or would it simply never be done by an accomplished practitioner?

Your expertise on this subject is appreciated.

Brad White_203

Oy!

The downside of such a configuration is a guaranteed collision of two streams of steam and associated saturated or condensed moisture. The collision will naturally force up such moisture into the steam distribution system.

If such a condition were to be tempting, I would use at least a dropped header, both to lower the amount of free moisture present but also to gain some height and "working room" for a proper system connection. Thus you have both avoided the collision, used "Thermodynamic Judo" to carry excess moisture right by that take-off and back to the boiler, and allowed yourself a proper take-off to the system with some bends for stress relief. Such a deal.

IF one had no choice (and that is a huge IF), I would follow that collision take-off into a second dropped and dripped header. I have seen large school boiler plants so configured and they worked fine, but had a 16-inch header with IVB drip traps along the length. Subsequent take-offs had relatively dry steam.

Now, "would this ever be done by an accomplished practitioner". That is an open question for no practitioner can control all of the variables encountered, especially and including the budget dictated by the customer. Given $X dollars, sometimes a steam fitter must make do and do their best. But given a choice and space to work? I doubt anything short of "by the book" would be done.

Here is a larger view though: Each of the facets of a good steam design, large boiler risers, using all available riser tappings, low exit velocities, dropped headers, generous equalizers, venting, proper A and/or B dimensions, etc. etc.... Each has their function and contribute to success.

Any one feature, if sub-standard might be forgiven in some systems due to greater benefit and performance of other system features. But at the same time, any one if sub-standard, might also render the other factors less capable and cause a cascade of negative effects.

My point here is, do all that you can as well as you can and depart from this with caution and an open mind to the potential effects. Each plays a role, together they work well. One delinquent can ruin the class average.

EDIT: I saw your other posting, with the photo of the boiler piped in copper. Much has been written about that practice. Most would not be permitted on this family-friendly site but might make it onto some large fortune cookie messages.

Bill_110

risers

Thanks for the explanation. I found corroboration on another site. In fact it mentioned that a lot of cracked boilers were associated with piping where the system takeoff was in between two boiler risers.