Condensate Vent Loop?

Steamhead (in transit)

and this setup is what I believe is called a "condensate transfer pump" a.k.a. "mechanically pumped accumulator tank". Its job is to pump the condensate back to the boiler room, thru a line that is not shown on your drawing, where the main vacuum pump would return it to the boiler.

See the diagrams on pages 191-192 of "The Lost Art of Steam Heating" for more.

Check to see what type of return pump is in the boiler room. And the pipe in question will definitely have to remain. You'll also want to replace those orifice traps with thermostatic ones rated for vacuum.

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Brad White_9

Condensate Vent Loop?

Hey boys and girls-

During demolition at a job now under construction, I got a contractor RFI on a discovered pipe. I went there yesterday to see for my self. Pipe is one-inch, was not insulated (perhaps abated years ago). It runs high tight to the structure in the basement and connects horizontally between two low pressure condensate lines (also one-inch size), each at opposite sides of the building. The points connected are about sixty feet apart. In the center, the line tees then drops to the top of an existing condensate receiver which is to remain.

From the point where this horizontal line connects, the condensate drops below the slab and heads to the condensate receiver from each side of the building.

The existing steam system which is to remain in this portion of the building is a low pressure two-pipe system with thermostatic traps mostly, some SS orifice traps more recently installed here and there. Pipe sizes are typically smaller than I expect to see for low pressure so thinking it was once a vacuum or vapor system. (It was originally installed in the early 1950's and serves a performing arts auditorium at a local university.)

I am suspecting that this line is an equalizing vent line such that it would ease any vacuum caused by one side of the building drawing/condensing more than the other and holding up condensate drainage in the other leg. My inclination is to leave it but the contractor would rather remove it for coordination purposes.

I have no photos but the attached sketch is as good as any photo I could post. The points of connection are that far apart; same information.

Thanks in advance for any ideas/validation/castigation.

Brad

Christian Egli_2

Extra pipes for extra profit; extra cynical

Here's what I understood. The condensate flows downwards on your drawing along both sides of the building, as in an ordinary dry return so typical of a two pipe large system. Then at the point where it becomes a dashed line this condensate line takes a dive and goes underground in search for the condensate pump.

Slopes are nice and easy to install and maintain above ground - not so in a buried conduit. Perhaps your underground lines where never even built as sloped dry returns, but simply as wet returns. In such case, any roller coaster ride would do.

Except that nothing will flow unless the pipes are properly vented (the exact same way we obsess endlessly about sewer drain lines) Here comes your mystery pipe!

At the dividing point, the afore dry return is separated into a wet return below ground and a dry only vent line stuck to the ceiling. Then, everything gets reconnected at the condensate pump, just because that's where you'd traditionally vent your system. If your pump sucks a vacuum, then the need to sequester your dry only vent is obvious. Another reason to keep a unique venting hole, is to prevent floods and whiffs of steam from occurring in an inconvenient place.

If your system in not artificially vacuumized, you could very well remove this vent pipe, but you still have to maintain the venting. For instance, removing the pipe and plugging the holes left on either side or your building would be a catastrophe. You imperatively need to keep an open vertical pipe rising to a safe flood level. You can't either put a steam vent or trap instead of the hole because that would cause havoc in the returns as soon as any one radiator trap goes faulty and passes steam.

The good news is that you can safely move this pipe anywhere you wish providing it can drain itself of any water. You can easily point it to the outdoors as well. I do not particularly believe there is any reason to keep a balance between the two return lines in the form of a connecting pipe specifically.

Does this building have a good trap maintenance schedule? And is the condensate pump fitted with a nice big open vent hole? (I have a picture somewhere of one such pump with a big fat make-do plug stuck in it; that's no good)

There, that's what seems to make sense to me. I have used, with great success, such dry only vent lines on problematic sections of dry returns.

Happy piping, and thanks for asking a long winded opinion of mine.

Brad White_9

Thanks, Frank

The condensate pump indeed is a transfer pump which goes back to the boiler plant in an adjacent building. Conventional Hoffman or Skidmore unit.

It is vented separately to atmosphere. The pumped condensate, when it gets to the plant goes into a deaerator then a BFU feeding CB low pressure boilers. Nothing special there. This all occurs upstream of the CP.

Because the receiver is vented, I am sure that this system no longer works on a vacuum at least at the building side.

I had suspected that this was once a vacuum or vapor system because of the relatively small line sizes on the returns.

One thought was that this line would equalize vacuum across two distinct sides of the building. The other thought was that it was akin to an air loop such as you would use when you take condensate around -and below- a doorway. Like that but on a larger scale.

If the system were in operation (seasonally of course) I would cap this "crossover vent" to see what would happen. When I see the entirety in my minds eye, I suspect I could remove it without harm. There is sufficient head from the traps above (this is in the basement) and the rooftop units have vents. (If it ever was a vacuum system, it sure is not now!) No heating problems have been reported.

Mercifully, this was once a stand-alone building and is now adjoined on two sides by newer construction so the load is less than it ever was.

Does anything I added above give you any ammunition towards removing it? I am not hell-bent on doing so, but if it is not needed, it would simplify the ductwork quite a bit.

Brad White_9

I think we see similar things, Christian

As you can see from my posted reply to Mr. Wilsey above, the receiver is vented, not a vacuum. May be an air loop but there are AHU's on the roof with vents. This line drops to where it connects to the LPR below the traps coming from the floors above. So it would seem to be a vent, not a drain.

What is neat is where the center tee occurs to head to the receiver: It is not a tee, per se, but the neatest 1" tapping welded to a 1" main that I have ever seen. Tiny welds, no slag not even grind marks. I am all but sure the line is dry. The horizontals to not pitch nor trap from what I can see. Hence I see it as a hold-over from days long past. I have no problem telling them to work around it or to move it while maintaining the non-pitch. But I see no reason why the condensate on either side would not flow with impunity either. A risk in removing a hassle in not.

Thanks for the discourse, as always!

Brad