Two Pipe Vapor System

Ted_Ryan

Purchased a 1930's house in the Poconos Mtns of PA.  The system is a Trane two pipe vapor system.  Looking to replace the boiler and perform maintenance on the whole system. Since I have given up finding someone that seems to know this system, I have read two of Dan's books and know just enough to be dangerous. 

Four questions:

1) The dry return has a Trane direct return trap located at the end.  The new system will have a vaporstat and be set at around 6 to 8 ounces.  Do I need to keep the direct return trap? 

2)The system also has a main vent located at the end of the steam main.  Isn't that a no-no on a two pipe system?

3)I see no evidence of an F&T trap anywhere in the system.  Is this appropriate?

4)All the radiators heat, however, I know for certain that no radiator traps have been replaced in at least 45 years.  Should I assume they are all busted and stuck open?  Can you reliably test the operation to leave them in place (if somehow still working) or should I just replace all the elements and start over (or should I just leave them alone until one of the radiators fails to heat).



Lot of questions and input on any and all would be most appreciated.

Dave in QCA

Trane System

First of all, congratulations on your new house and the great heating system that it features.  You WILL like it!



Here is a link to a publication on the Trane system.   http://www.heatinghelp.com/files/articles/1392/26.pdf  



To answer your questions.

1.   Theoretically, as long as your vapor stat is working correctly you don't need the direct return trap.  However, it doesn't hurt anything to leave it in place.  Under normal conditions it just sits there empty.  If however, there is an increase in your boiler pressure to a point that the condensate cannot return, it will fill up with water and if it still functions correctly, the float will trip the valve and allow steam to push the condensate back into the boiler.  My recommendation would be, since you have it you might as well keep it.  You could test it out to see if it works.



2.   Some vapor systems used crossover traps as vents on the steam main.  However, this booklet indicates that Trane used float type traps fitted with check disks.  These would be similar to a Hoffman 76.  If those vents still work, they would be fine.  If you want to maintain the vacuum vapor operation, if they need to be replaced I would consider using Hoffman 76.   GASP! Cough!!!    I know I have just committed heresy in the Gorton club, but remember, in a vapor system, as long as its tight and you are able to maintain the vacuum, fast venting is not such an issue because once you the air out, you keep it out, and steam travel in subsequent cycles is incredibly fast.



3.   The Trane system did not make use of an F&T trap in almost all cases.  That is true for most vapor systems as well.



4.  Good that all radiators heat.  The traps may actually be OK.  The sylphon type bellows that Trane invented work quite well for a VERY long time.  When traps fail, they sometimes fail open and sometimes closed.  Yours have not failed closed.  The only way to see if they have failed open is to run the boiler for an extended period of time to the point that all of the radiators are heated.  If you have traps failed open, you will get steam going down the return lines.  The temperature of these lines is normally warm or hot for a few feet.  However, steam hot is VERY hot and the return lines should not be like that for more than a foot or two, if at all.  If they check out OK, leave 'em alone.  If you do have to replace, I would get the correct insert for the original trap or refit it with a Barnes and Jones cage unit.  Either will give you the same performance as the original trap, or at least very near to it.  This is important because some new traps that have low venting characteristics would cause your system to become imbalance and restrict the venting and therefor the heating on the radiator on which it was installed.



Good luck with your system!!  Keep us posted on your progress and observations.

JStar

Trane

I'm in NJ, but will travel to PA if you need on site help with your system.

vaporvac

No Traps on Trane

Hello,

I, too, have a Trane VaporVacuum system and it has NO traps on the radiators.  It was designed that way.  I only found this out after being told my system was stupid and couldn't possibly work as it needed traps on all the radiators. Glad I found this forum with its many helpful and patient members! It seems, many Trane systems have orifices at the steam inlet; perhaps yours does, as well.

Mine also has the one vent at the end of the line that looks like something on an old steam train. Nice to see someone else here with a similar system to compare notes with!

Pictures  would help and everyone like seeing all the different systems out there!

Colleen

Ted_Ryan

Follow-up

Thank you all for you comments. I have attached two pictures.  The fist picture is the near boiler piping for the wet and dry returns. (Sorry about the copper..working to get that out of there!) There are two dry returns that connect at the upper right of the picture.  There is a hoffman vent on top of the tee where they connect. (Not a good location)  This connection has one large pipe that drops to the floor and another that connects to the direct return trap.  The direct return trap is the second picture.  The trap has a topside connection that runs over and attaches to the top of the boiler.  The bottom of the trap connects down to the wet return.  Notice the series of check valves across the bottom.  Not sure the logic of this.  Any thoughts on how this is plumbed would be appreciated.



Regarding comments about radiator traps not being part of the vapor system, all of my radiator (except one interestingly) have trap bodies on the output side of the radiator.  I have not opened one up to see if there is an element inside. 



Maybe I have jumped to an incorrect solution about the type of steam system in the house.

Steamhead

I'm sure your traps still have their guts

the key is that there has to be SOME way to keep steam out of the dry return. Traps are the most usual method, but some systems (Broomell and similar) use water seals, others use supply-side orifices. Trane used traps on their older systems but later (1930s-40s) ones used orifices. These later Tranes, like the Arco Model K, the Thermal and other orifice systems used the principle Frederic Tudor patented in 1885.

Dave in QCA

Operation of Direct Return Trap

If I open your pictures in a separate window and then zoom to 200%, I can see a lot of detail as to what is going on.



Regarding the check valves, they are a critical component of the direct return trap, it will not work without them.



At the left side of the picture that shows the piping, I can see two "end of main" dry returns.  It is important to differentiate what kind of dry returns you have on a two pipe system.  A dry return is technically any return line that is above the water line of the boiler.  The end of main returns will also contain steam and will be at a pressure equal to that in the boiler.  The dry returns on the return piping will be at atmospheric pressure almost always.  They carry both condensate and air out of the radiators. 



The problem that the direct return trap addresses is how do you get condensate to flow from a pipe that has no pressure into a boiler that has pressure.  Remember, that each pound of pressure equals about 30" water column.  So, at one pound in the boiler, if the water is stacked up over 30" in the return line, it will flow into the boiler, and at 2 psi, 60" and so on.  At 2 psi, you probably don't have enough head on the return piping so the direct return trap deals with that problem. 



Here is how it works.  Normally, at low boiler pressure, say 8-16 oz, the condensate coming back through the return lines will fall down the vertical pipe, flow through the first check valve, flow past the tee that leads up to the bottom of the return trap and on through the second check valve and into the boiler return piping.  As long as there is little or no boiler pressure, it operates on gravity flow as if the check valves and return trap were not there.   Keep in mind also that the end of main returns are always about the same pressure as the boiler itself, so condensate coming back from the steam mains also flows into the boiler.  It is important that any horizontal section of the end of main returns be 28" higher than the boiler water, or well below the boiler water line.  This is because of the so called dimension "A", but that is another subject.



Now, if the boiler pressure starts to climb, say to 2 psi, what happens?   Well, the condensate coming back from the return piping does not have a tall enough column of water to create sufficient pressure to cause it to flow into the boiler.  The check valve to the left of the return trap is closed by the pressure in the boiler.  So, no boiler water is flowing backward through that low horizontal pipe.  As the condensate is returning from the system, it flows through the check valve on the right and then upwards into the return trap vessel.  At this time, the vent port at the top of the return trap is open to the return piping so as the condensate flows in, the air is vented into the return piping and out of the return piping vent.  As the water rises in the return trap, there is a float that slides up a rod.  When it gets to the top, it causes a small valve to trip.  This simultaneously closes the vent port and opens the steam port.  (That is the small pipe that comes from the top of the boiler)  At this moment, the return trap is now pressurized and its pressure is equal to that of the boiler.  This pressure causes the check valve to the right of the return trap to close.  Since the condensate in the trap is higher than the boiler water level, it falls by gravity, through the check valve to the left and into the boiler.  As soon as the water level in the return trap falls, the float drops, and the internal valves switch back, thus cutting off the steam, opening the vent and putting the condition of the return trap back at atmospheric pressure and thus allowing condensate to again flow into the trap from the system.



This is all rather ingenious!  Since the return trap only vents through the return piping vents, if you are using vacuum vents you can operate this system as a vapor vacuum as it was intended.



With a good vapor stat, you can keep the pressure from climbing above 8 oz.   But, the return trap would be a good element of extra protection.   For many years, contractors encountering a 2 pipe system would install a condensate return pump and tank at a cost of over a thousand dollars.  They didn't know about vapor stats or didn't think that the system could really work at less than 2 psi.



I believe that Hoffman still makes a return trap device, but it is extraordinarily expensive.  I just looked for a reference for it and cannot find it at the moment.



I have an old Dunham Vapor Vacuum (Home Heating) system.  It has been cobbled through the years.  I am presently in the process of finalizing plans to replace the boiler and otherwise restore the return piping of the system, eliminating the return pump.  I sure wish I had the missing Dunham components.  I think you're pretty lucky to still have the Trane return trap and if it were mine, I would certainly keep it in place!

Ted_Ryan

Direct Return Trap Model 210

Dave thank you again for your detailed comments.  After looking at the Trane booklet and my return trap, it looks like somewhere along the line the gauge glass was removed and the openings plugged.  Do you know the purpose of the gauge glass and would it be worthwhile to attempt to get it replaced?  Thanks.

Dave in QCA

Visual Indicator

The purpose of the gauge glass is to give a clear visual indicator of the water level coming up into the return, of it being expelled, or of its absence alltogether under normal no pressure conditions.  It does not change how the return trap functions.  If you wanted to replace it, you could install any water gauge glass setup, assuming that you can get the plugs out of the trap.

Ted_Ryan

Benefits

Assuming the plugs can be removed, sounds like it would be a worthwhile exercise to be able to monitor the performance of the direct return trap.  I know I was leery of taking the trap apart to see if the insides were functioning for fear of not being able to get it back together tightly.

Ted_Ryan

Hoffman 76's

Regarding the main and return vents, you recommended Hoffman 76's to preserve the vacuum. Looking at the Trane booklet, it looks like Hoffman vents on both the steam main and return.  What is the consequence of having a high capacity standard vent like a Gorton 2. 

In the Trane booklet there is also a damper regulator.  On my system, I see no evidence of this part.  Would this be integral to the boiler? 

Ted_Ryan

Checking Traps

Steamhead thanks.  In checking the operation (they are definitely open, just not sure if they close) of these traps, I have the ability to get into the craw space and, assuming I am not bitten by a brown recluse spider, measure the temperature of the return several feet away from the trap.  Any ideas on how warm the pipe should be at that point.  It looks like the traps are all B-1 bellows type.  TR.

Dave in QCA

Trane Vents

The original Trane vents had a vacuum check on them.  I believe that the only main vent on the market that has a vacuum check is the Hoffman #76.  The Gorton #2 is a great fast vent, but it will not seal against vacuum.  Many say that the old vapor systems should only be run in vacuum if firing on coal.  However, there continues to be a lot of discussion on that subject.



The old trane systems also had a mechanism that controlled the draft on the boiler and also a check damper on the chimney pipe.  Those would have been removed with the old coal fired boiler.  They would serve no purpose now.  Yes, while not intetral to the boiler, it would have been closely piped to the original boiler.

Steamhead

They should not approach steam temperature

but if they just get warm, that's OK.