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Two pipe Steam with no traps

Hi Heating Help Folks

I’m a manufacturers rep in Kansas City working with a local contractor to solve issues with a boiler they recently retrofitted in a 1500 sq. ft two story house. This is an unusual two pipe steam system with no traps.  The radiators are also unusual in that  the inlet and out are both at the bottom.  The new boiler is a Crown BSI-138 rated at 138MBH input.  There are two 2” mains, one covers the front of the house, and one covers the back of the house.  both mains are pitched back to the boiler. Both mains have a ¾” dry return that runs parallel to them.  These returns are at the same level as the mains

The radiators do not have air vents, with the exception of one radiator.  No one is sure why or how that vent got there.  The contractor also installed a Barnes & Jones VB series vacuum breaker where both dry returns tee together before they drop down to the boiler.

They are currently running the boiler at 1.5 psig cut out, and 1 psig cut in.  The new boiler was installed with a Hartford Loop.

The problems are as follows:

1) There are two radiators at the end of the run on the back side of the house that won’t heat.  The contractor pulled the plugs on these radiators to vent the air and eventually got heat to these radiators (but I suspect only temporarily). We noted that there was water hammer while these units were being vented and heating up.

2) We also have a considerable amount of water that

is backing out of the boiler every time the boiler fires. This is tripping the

LWCO and causing extreme short cycling. We suspect that water is backing up into the dry returns.

does anyone know what kind of system we are dealing with here, and how it can be made to work?  Should it be run at very low pressure with a Vapor controller?  Not sure why they put a vacuum breaker in there… should we replace this with a main vent?

I attached a couple pictures of the original installation.  I can get photos of the new installation if anyone would like to see those as well




  • vaporvac
    vaporvac Member Posts: 1,520
    I spy...

    a Trane? first of all I'm a homeowner, so take what I'm saying as you will. I believe pictures of the new boiler and its piping (from many different angles and distances) would go a long way in trouble-shooting your problems. Could you also get a close-up of the rad valves? Are the all the same? Did they skim the boiler? How is the water line?

    What I can say is that this is an older Vapor system like my own which doesn't have traps and should be run on low pressure. There may be orifices in the valves. I've never seen the ones with the inlet and outlet at the bottom, but know they exist. However, I think I spy a Trane Air Eliminator in the background which, if so, would make this a Trane Vaporvacuum system like my own, that is designed to run on a naturally induced vacuum. This speeds heat to the rads and keeps it even and long lasting. Why did they install a vacuum breaker?

    You can read about this system in the literature on this site to get some background. I'm sure the pros will chime in with other pertinent questions and comments. C.
    Two-pipe Trane vaporvacuum system; 1466 edr
    Twinned, staged Slantfin TR50s piped into 4" header with Riello G400 burners; 240K lead, 200K lag Btus. Controlled by Taco Relay and Honeywell RTH6580WF
  • will smith_4
    will smith_4 Member Posts: 259
    Curious system

    Set us up with more pics of the boiler piping. Maybe I'm seeing things (or NOT seeing things-lol), but it seems to me that there is only one supply leaving the boiler to the two headers, and it kinda looks like maybe 2" copper.  Can't see where the LWCO is, but I'm wondering if the low water trip isn't because water is backing out of the boiler (tough to do if the Hartford loop is there-and done right), but rather a slanting water level. When the boiler fires and you come up to steam, with only one supply, the water can tend to slant in that direction. The LWCO might be seeing this, depending on where it's physically located. With low water content boilers, it's usually recommended to go with two supplies, then into the header/equalizer. If it is slanting, you run the risk of overheating the rear section/s. Could also be caused by poor water quality leading to carryover or foaming. Could be caused by over firing. Let's see some more!

    By the way-I've only seen a few systems like that one-2 pipe with no traps. Rarer than hens teeth. One I remember, a contractor had put traps in before we looked at it- thinking someone else didn't know what they were doing (80 years ago). Didn't work so well for them. Here's a pic of a device I found in that system that even stumped The Wall back when I ran into it...
  • vaporvac
    vaporvac Member Posts: 1,520
    Funny you should mention that...

    I had multiple companies suggest I put traps on my similar system saying it couldn't be working right. I figured I lived in a house built by someone who would only have had people who knew what they were doing, so I showed them the door. Thank goodness. It's a pleasure not to have the worry of traps and vents on the rads. I'm wondering if that's another iteration of the Trane mercury pot. Hopefully, someone can recognize it now.
    Two-pipe Trane vaporvacuum system; 1466 edr
    Twinned, staged Slantfin TR50s piped into 4" header with Riello G400 burners; 240K lead, 200K lag Btus. Controlled by Taco Relay and Honeywell RTH6580WF
    RDSTEAM Member Posts: 134
    Start by

    Getting that system back to running at around 1/2 psi max. I would get a vaporstat and a nice low psi gauge. Do you have all of the old rad valves? If there's any that have been replaced and the existing orifice was removed you may still have a slight problem. Also get us a pic of the near boiler piping.
  • Mike Kusiak_2
    Mike Kusiak_2 Member Posts: 604

    Its really hard to tell from the photos, but it appears that the riser from the boiler is piped directly into the two  mains without a header or equalizer?

    If this is true, then it will be very difficult for any carried over water to return to the boiler.

    A closer shot of the boiler showing the riser and near piping would be helpful.
  • WJurgens
    WJurgens Member Posts: 7
    The Plan

    Thanks for all  the feedback.  I will post pictures of the new installation as soon as we can get back out there, along with close-up pictures of the radiator connections.  Our plan at the moment is as follows:

    1) Install Honeywell L408J1009 Vaporstat, and run boiler between 5 - 8oz

    2) remove vacuum breaker and install Hoffman 75H main vent

    3) Install low pressure 0-32 oz  gauge on the boiler

  • WJurgens
    WJurgens Member Posts: 7
    Added vapor stat, still short cycling like crazy!

    we added the 75H Hoffman vent, and the Honeywell vaporstat to the system and ran the boiler at low pressure.  still need to put the low pressure gauge on there, but that just came in today. 

    we are still short cycling like crazy, and now it is on pressure.  The 75H is venting but it seems to be not nearly fast enough.  we tried widening the differential on the vaporstat as much as possible, but that didn't help short cycling much at all. 

    we were having trouble getting steam to the back side of the house before, and now running at lower pressures it seems to be worse. It took well over an hour to get steam 1/3 of the way down that main. We tried adding a couple of Hoffman #40 bullet vents to two of the further radiators on the back side.  that didn't seem to help much either

    I did a radiation count to see if boiler oversizing might be contributing to the short cycling. I came up with 299 sq ft. of EDR or 71,760 BTUH. The boiler is a  Crown BSI138 with a net rating of 85MBH.  So it looks pretty good. 

    It seems like our boiler short cycling is being caused by air being traped in the radiators and mains.  The 75H mounted back at the end of the returns doesn't get air out quick enough to keep the boiler from hitting pressure after 15-20sec and shutting off.  The pressure will the drop down and the boiler will be back on after about 30-60 seconds.  It seems to me like we need some vents that will get the air out of this system very quickly so the radiators can get engaged. 

    so my question is, what vents should we be using?  Is there something special for these low pressure systems? what about vents on the radiators? should we be using those?

    I attached pics of the newly installed boiler and some close-ups of valves on the radiators. 
  • vaporvac
    vaporvac Member Posts: 1,520
    No vents on rads!

    I'll leave it to the experts to comment on other aspects, but I know that two-pipe systems should NOT have air vents, especially those without traps. Take them off and see what the pros say about getting heat to all the rads and stopping the short cycling. BTW, was that a Trane Air Eliminator Isaw in the background? Don't get rid of that, if so. My system is amazing and this one can be too!
    Two-pipe Trane vaporvacuum system; 1466 edr
    Twinned, staged Slantfin TR50s piped into 4" header with Riello G400 burners; 240K lead, 200K lag Btus. Controlled by Taco Relay and Honeywell RTH6580WF
  • JohnNY
    JohnNY Member Posts: 3,208
    Leaving it to the experts.

    There are lots of 2-pipe air vent systems out there so be careful where you place your CAPS.
    Contact John "JohnNY" Cataneo, NYC Master Plumber, Lic 1784
    Plumbing in NYC or in NJ.
    Take his class.
  • EzzyT
    EzzyT Member Posts: 1,269
    Near boiler piping and venting

    Both 2" trappings should've been used going into a 3" steam drop header letting that wet steam separate in the header to send dry steam to the system. Hartford loop looks no good there should be a close nipple instead of that union and reducer coupling. Need to upgrade the venting too that one Hoffman #75 isn't going to vent enough air out of that system you wanna get that air out of the mains and returns as quick as possible so more vents are needed. What's are measurements of your mains? Size pipe and length in total?

    Those vents on the radiators need to be removed and tappings plugged. Check if the radiator valves still have the orfice place if they do don't remove them if not you can always make your own orfice plates with a hole punch.
  • Double D
    Double D Member Posts: 441
    edited February 2014
    More pics

    Post pictures of the end of the mains. Also when you say "The contractor installed a Barnes and Jones VB series vacuum breaker where both dry returns tee together before they drop down to the boiler". Post a picture of that. Stand back far enough to get as much as you can in the picture. I see you now have the Hoffman 75H but still post the pics where it's tied together.
  • WJurgens
    WJurgens Member Posts: 7
    end of main pictures

    Here’s a couple shots of the end of mains. The mains are both 2”.  The main on the front side of the house is about 15’ long.  The main on the back side of the house is about 25’ long. 

    The Barnes and Jones vacuum breaker was installed when the new Crown boiler went in a couple weeks ago. I have no idea why the contractor put it in,  we never recommended it.  It was removed and replaced with the Hoffman 75H at the same location where the returns come back in tee together before they drop down.  You can see it in the overhead shot of the piping in my earlier post

    EzzyT,  Is there a particular vent that works well for these low pressure vapor systems?  Seem like the Hoffman 75H is venting very slowly with only 8-16oz if pressure behind it.  Would you suggest putting two vents at the end of the supply mains?  And perhaps also at the end of the returns back at the boiler?
  • gerry gill
    gerry gill Member Posts: 3,072
    i can't tell from the pictures,

    but are the outlet pipes from the radiators the same size as the inlet pipes or smaller?
    Serving Cleveland's eastern suburbs from Cleveland Heights down to Cuyahoga Falls.

  • gcp13
    gcp13 Member Posts: 122
    back pitched returns

    does the outlet on the radiators drop into a wet or dry return

    if that is the dry return with all the stuff hanging on it i hope its not back pitched

    causing water to build up and stop the steam

    i have a two pipe without traps that is piped into a wet return an all radiators need

    airvents and very low pressure, with a false waterline to keep the return under water
  • WJurgens
    WJurgens Member Posts: 7
    supply and return sizes

    the supply risers to the radiators are 3/4", and the returns from the radiators are 1/2"

    all returns from the radiators drop into dry returns.  The returns run parallel to, and at the same elevation as the supply.

    we looked at the supply and return mains for any obvious sagging and it all looks good.

  • gerry gill
    gerry gill Member Posts: 3,072
    whats the inside

    of the union elbow and the inside of the inlet valve look like.
    Serving Cleveland's eastern suburbs from Cleveland Heights down to Cuyahoga Falls.

  • WJurgens
    WJurgens Member Posts: 7
    vent the mains!

    here's what the latest plan is shaping up to be

    add 1/2" ball valves to the end of each supply main and also where the returns tie back together.  we'll do an experiment to see if we can keep the boiler from short cycling by using some or all of these vents to get the air out quickly. we'll also be looking at how quick we can get steam to the radiators.

    If we have to add additional air vents  to the end of the steam mains we'll go with Hoffman 75's as opposed to 75H's.  The 75's are designed for lower pressure and as such should have a larger orifice and vent air more quickly

    has anyone done an experiment like this before?  your thoughts?


  • Steamhead
    Steamhead Member Posts: 16,287
    Gorton #2 main vents

    will outperform those Hoffmans. 
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service