One-pipe system with steam traps and a raised boiler

Answerman · March 2016

Today I inspected a building with one-pipe steam, a wet return, no condensate pump, and F&T steam traps on the drip lines in the boiler room. I was surprised to see steam traps in a one-pipe system with no condensate pump, so I asked the super about it.

Turns out, the boiler used to be sunk lower than the current boiler room floor, roughly 3 feet lower according to the super. When the boiler was replaced a few years ago, the installer decided to raise it up. Apparently that caused severe water hammer throughout the building, mostly up to the first floor. It was mainly on startup, after the boiler had been running for a few cycles, and as long as it continued to run frequently (as in cold days), the hammer went away. So they installed the steam traps. Apparently that helped a lot, but there is still some water hammer.

I'm wondering what, if anything, I should be recommending for this system. It sounds like the current situation with water hammer is still problematic (even though they seem to have accepted it), and I'm not sure if the steam traps could be hurting the performance of the system in some way. I'm thinking perhaps install a condensate tank and pump, and maybe a couple large steam traps right before it (instead of the smaller ones spread out, even though there aren't many- I only counted about 4 in the boiler room and one elsewhere) I hate to recommend another energy using item which will require periodic maintenance and repair, but if it will improve the system, so be it.

Any thoughts? Short of lowering the boiler again..

Answerman · March 2016

In case it matters, the master venting is also thoroughly inadequate, with just a few whistling Hoffman forty-something vents throughout the basement.. We will of course be recommending better venting.

The operating pressuretrol was set between 1-3psi, so nothing crazy (it's better than most buildings of this size I've seen..)

Jamie Hall · March 2016

Have to admit that I'm a bit surprised by the traps, too... shouldn't really need them, assuming that the wet returns really are wet. After all, ideally the condensate should jut go down the drips to the wet returns and flow back to the boiler. Unimpeded.

They may be related to the water hammer, though, if they are located in such a way that the condensate backs up into the steam mains where it doesn't belong. One only gets water hammer if the condensate can't drain out of the mains! So I would be inclined to first check all the pitches, and then make sure that you have enough vertical distance above the traps to the mains so that water can't possibly back up.

Also the near boiler piping, to make sure you are getting reasonably dry steam.

One thought -- when they raised the boiler, is there still enough height above the boiler to avoid backing water out of the boiler under pressure into the mains? At three psi, you need a good 8 feet of headroom... If you lower the pressure to, say, 1 psi (28 inches or so) does that help any?

776v63 · March 2016

Recently read Dan's book The Lost Art Of Steam Heating. Lets see what I learned.

Sounds like the classic "Take the boiler out of the pit" story. The system was "fine" until the new boiler was installed, then it suddenly hammered like crazy. All else being equal, the "A" dimension is probably inadequate and water is being pulled into the mains or flooding from the wet return.

On a one pipe gravity system, introduction of F and T traps causes the condensate to stack higher in the wet return because there is no left over steam pressure to help push the condensate into the boiler. So the addition of the traps is actually an additional problem to deal with.

If the A dimension is close to where it should be, verify the pressure is nice and low. It shouldn't need to be any higher than 1.5PSI

Answerman · March 2016

Thanks for all the comments!

What I don't get is, why did installing the traps help? The super, who seems reliable, reports that installing the traps helped a lot with the water hammer (He said that before the traps were put in, it was so bad that he found bits of metal in the condensate water!).

It makes perfect sense that raising the water line could cause water to back up, and I would expect that traps would make it worse.

I should clarify, that F&T traps are not installed everywhere, only in the boiler room, and one nearby storage room. The boiler room is lower than the rest if the basement, and the traps are installed before the vertical drips, only a little higher than the steam header (see photo in the original post).

I should also mention, that there appear to be wet returns on the floor throughout the basement, that originally must have been dry returns. I say 'appears to be', only because with the slope of the basement floor, it's tricky to compare the water line to the level of the return piping. But I'm pretty sure those returns are wet

Paul48 · March 2016

Is that a main coming off the side of the header?

776v63 · March 2016

Are the individual traps serving individual appliances?

It's hard to get a clear picture of what's going on without pictures, measurements, or diagrams.

As far as the traps helping the hammering; sometimes one problem may mask symptoms of another. That doesn't mean it was the correct solution. There are still problems right?

The traps weren't there before. Presumably the system works correctly without them before the new boiler was installed.

Paul48 · March 2016

I'll add a vote to the fact they have lost their "A" dimension. The original installer was smart enough to realize he wouldn't have it without the boiler being in a pit, or, other-wise lowered. I'd suspect that there were other changes made at the time the traps were installed, that they were not aware of. And those changes are what reduced the banging. They may have reduced the pressure drastically form what it was set at, or down-fired the boiler.

One-pipe system with steam traps and a raised boiler

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