Replacement air vent for condensate return

outofsteam

I have a two pipe steam system with gas fired boiler and condensate pump in a large building. This antique Trane float vent on the high point of the condensate return line furthest from the boiler seems to have failed, and begins shooting a 2’ jet of water from the top once the heat has been on for about 24 hours. My question is, would a Hoffman 75 or 75H be better, or is there a more ideal vent for this application?

Jamie Hall

A 75 would work -- but keep in mind that that vent on the "condnsate return" is actually the main vent for all the radiators. I'm not sure it would really be big enough, unless you have a well-calibrated and controlled vapour system. On the other hand, you're going to have an interesting time if you wanted to mount something bigger... kind of cramped. A rather fancy selection of elbows and nipples night give you room for a Gorton #2, which might be a better choice.

outofsteam

That makes sense, thank you; I had been considering whether the gorton #2 would be better. I don’t have a problem building out an elbow/tee/nipple arrangement to accommodate it, but I was unsure how it would handle the condensate load. I will go ahead and order the gorton and some pipe fittings.  The system does need a good bit of tweaking before I would consider it well balanced; this summer I need to go through all the steam traps (probably going to put in cage units), and I have several radiator valves leaking slightly throughout the building. I had been considering swapping the leaky valves with thermostatic valves, at least those that are not in rooms with thermostats (there are several zones, each controlled by pneumatic thermostats, some of which are also not working properly).

JUGHNE

On a 2 pipe system wouldn't this be considered a true "dry return".

And the vent on the condensate pump be considered the air vent for the entire system.

The pump may not have been there for the original boiler system which could have been gravity return?

Could you have slow return to the pump that the water builds up in the return?

Jamie Hall

Yes, it would be a true dry return. I've been avoiding using the term...

There is a condensate pump? Argh. Missed that. Well, yes the vent on that could be considered the main vent for the whole system -- but only of the dry returns empty into it above the water line so that any air in them is never blocked. If they get there though pipes which are below the water level in the receiver, then that won't work.

JUGHNE

If the piping below that point does not trap water in a loop seal then the air would go to the pump.

If that is so then, in theory that vent could be an open pipe as the cond would drain by gravity to the pump.

But if a water seal is after that then the vent is needed.

IMO, with a 2' geyser of water there seems to be a clogged/slow drain line.

outofsteam

It is the only vent ahead of that condensate pump, which has no vent pipe in and of itself; that vent is above the main water level, albeit on the other side of a gymnasium. So I believe there is a water seal created; from the condensate pump it goes right to the makeup feed. A clogged or slow section of the line is possible… I’ve followed that pipe as far as I can; it has a number of drains that run into it past that point, and then it disappears into a cinderblock wall and runs behind the finished walls of two bathrooms before reemerging from the concrete floor near the main condensate pump. Is there a good way to identify sections of pipe that are more likely to be the problem? And more to the point for my current issue, will the gorton close itself off if the same backup occurs? From what I’ve read they are great for steam, but I haven’t come across a strong statement one way or the other as to whether it would close successfully under the existing conditions, and while I will no doubt replace the air vent at the end of my actual steam main with the Gorton #2, I had considered a float style vent for this return pipe due to the water backup issue. 

JUGHNE

All install instructions I have seen for cond pump or feeder pump require a high vent to open air. Also an overflow pipe set just above the boiler water line.

There are labeled warnings of the tank exploding if not vented.

But your system is trying to have cond water flow by gravity into a somewhat pressurized (unvented) tank....until the float operates the pump.

The vent might help the water return and reduce the water geyser.
And if you can see steam leaving the vent pipe you know you have traps failing somewhere.

The Gorton # 2 have a float to close against water....which they should not see much of. I would pipe it as high as practical to avoid water and water hammer.

JUGHNE

If it appears, that what you have is the only vent for the steam main, you may want to pipe as such with the potential to add more venting.

This has multiple air vents with strainer and blow down valve.
These 4 vents pretty well max out the capacity of the 3/4" pipe that comes off the EOM.

outofsteam

Thank you! That clears up a few things I had been trying to figure out. Upon further inspection, there is a vent pipe that goes up from the condensate pump, and it has a tee above the boiler water line to an overflow pipe. So you were dead on about it having/needing the vent pipe, I just didn’t see it the other night. However if that’s not adequately relieving the pressure from the condensate line, I assume that makes a clogged or slow pipe between the vent and the pump much more likely. I will keep an eye out for steam from that open pipe next time the system is on; I have it off right now to replace a pneumatic thermostat. And I like the arrangement you depicted with the wye and multiple vents; I will set up something like that with this first gorton #2, and no doubt add on as necessary. Question though: since the current vent I’m working on is on a return, would it still be considered an end of main vent? I have other vents on the ends of the large steam headers, which no doubt will also need attention at some point, as they are also older float vents (sarco 6T, I haven’t taken one apart yet to see if they’ve had the 6A conversion done).

JUGHNE

BTW, that "wye" is a strainer to protect the vents.

You said vents on the end of the large steam headers....do you mean a branch of the steam main? Which I assume the vent in your picture is on a branch EOM.

Jamie Hall

No, a vent on a return line would not be considered an end of main vent. However, it might be considered a main vent. In any case, in a two pipe system it is one of the principal vents on the system -- main or not -- since it is responsible for venting the air pushed out of the radiators.

Perhaps we should take a step back here, though, and go over two pipe steam systems a bit.

First, and most obviously, there will be steam mains, and from them there will be runouts to the various radiators. They carrey steam at more or less boiler pressure. So far so good.

Next there will be dry returns. These accept the return lines from the radiators and will carry air and condensate from the radiators. They should NEVER have steam in them, and they should run at atmospheric pressure or very very close to it. These are usually, though not always, parallel to the associated steam mains.

And last there will be wet returns. These will be below the boiler water line; often at or very near floor level. They are always filled with water. Indeed, for proper functioning of the system they must be water filled, and the water level when the system is off must be at the boiler water level. As we will see in the next paragraph or so, serious problems can occur if they are not water filled properly.

Now there are also vertical pipes, referred to as drips, which carry condensate from either the steam mains or the dry returns down to the wet returns. They are found at all low points of both the steam mains and the dry returns -- indeed, it is very common for them to be a pair at the end of the steam main and its associated dry return. Note, and this is important, if the water level in the wet return is too low, steam will blow through from the steam main into the dry return, pressurizing it, and the ssytem will work poorly -- if at all.

If there is no convenient wet return, you may find a pair of vertical pipes arranged in a loop to the floor, connecting the steam main and the dry return. This will carry condensate, but not steam or air from the steam main to the dry return.

OK. So much for pipes. How does air get out of such a system? First, the steam mains. There are two approaches to getting air out of them. In some cases, they will have crossover traps at their distant ends which connect to the associated dry return. These may be ordinary radiator traps, or they may be larger, but they are arranged above the steam main usually with a short nipple going up vertically, then a horizontal nipple to the trap inlet, and then a vertical nipple down from the trap outlet to the dry return. An alternate arrangement is for there to be one or more main vents in the same location on the steam main.
'
The dry return(s) must also be vented. Usually this is done after they all join together at or near the boiler before they drop to the boiler inlet with a main vent or vents.

So much for the normal two pipe system.

Now -- at some point you seem to have acquired a condensate receiver. This complicates matters considerably, as it is vanishingly rare for that to be high enough to keep the water level in the wet returns at the level it needs to be. What this means is that every single drip from a steam main must have an F&T trap on it, or equivalent, to ensure that steam does not get into the wet returns and thence into the condensate receiver. These traps are NOT substitutes for the crossover traps or the steam main main vents, whichever is used. Nor are they optional. Much mischief will occur if they are missing or not functional.

Further, as others have pointed out, the condensate receiver must be vented to the atmosphere, and must have an overflow near the boiler water line.

If steam is seen coming out of the condensate receiver vent, one or more of the traps on the system is failed open, and it will be necessary to find it and fix it. This could either be one of the radiator traps, the crossover traps if used, or the F&T traps on the drips.

Control of the condensate receiver is simple -- but, curiously, often done incorrectly. The condensate return pump from the receiver to the boiler must be controlled by the water level in the boiler, by one of the low water cutoffs. The water level in the condensate receiver, in turn, is controlled by a float valve or float switch, which allows makeup water to feed when the condensate receiver level is low.

This is the reason for the overflow from the receiver: if the condensate return from the system is slow, it is possible for makeup water to be required during steaming, but when the condensate does return, the tank will now be too full. To prevent overfilling the boiler, that excess water must be allowed to overflow to waste.

These systems are very simple, however, if the purpose of the various pipes, vents, and traps is not properly understood they are equally simple to mess up.

I suggest going through your system from end to end, identifying which of the categories the various pipes fit into and how they are vented and how they get back to the boiler, and what each widget you encounter is supposed to do -- and which may have been added in an attempt to "fix" something. Then begin to work on fixing -- correctly -- whatever isn't working properly isn't connected properly.

I hope all this helps.

dopey27177

since you have a condensate pump which is vented to the atmosphere get rid of the wet return and make all dry returns them all dry returns. Once that is done there is no need for vent valves on any of the returns in the basement.

There vent for the dry return is a pipe screwed into the top of the tank and raised up about five feet.
get rid of all the vent valves in the basement. Before doing that fix or replace all the radiator steam traps. That way the returns in the basement will see only condensate and air.

Jake

Jamie Hall

Only warning on that, Jake, is to remember to isolate any steam main drips...

dopey27177

Ah yes forgot about that one. The steam main drips could have a 1” or 3/4” f&t steam trap. Both traps remove the same amount of air and condensate.

At 81 one sometimes I forget something’s.

Haje

outofsteam

Thank you all for your insight and feedback. Jughne, the vent pictured is on a dry return. There are different vents at the ends of the steam mains. I have replaced it with a gorton #2, elevated from the original location, but the vent itself is leaking significantly still. Not quite the geyser that came from the failed vent originally pictured, but still a notable rush of water when the backup first hits followed by a steady drip.

Jamie, thank you for the condensed rundown; that was quite helpful, and has led me to consider a second possibility rather than the pipe being clogged. There are several radiator steam traps as well as F&T traps from the mains downstream of that vent location, I am wondering if one may be stuck open, thus pressurizing the line ahead of the trap and causing the water backup. 

Jake, interesting concept about getting rid of the wet return… I don’t know if my particular situation would allow it, but I’ll look into it. What could be considered the basement is a finished space; the level with the boiler consists of a gymnasium and stage, with radiators mounted below the water line, which I believe is what necessitated the condensate pump on that end of the building in the first place (there is another one as well, located in the crawl space under the other wing of the building, which is still higher than the basement level; it’s an unusual layout).