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Help Needed Understanding Hybrid One Pipe System

BenL Member Posts: 4

Hi all,

I’ve never posted to Heating Help before, I’d never heard of it or Dan Holohan until a few weeks ago. I’m absolutely blown away with what a good resource this website and ‘The Lost Art of Steam Heating’ book is. I have 10 years of experience as a pipe fitter and have worked on various commercial/ industrial steam systems repairs and boiler replacements, but the last few weeks has me pretty confused and I can’t seem to find a recommendation for my customer.

I received a call from a customer who purchased an old building and wanted me to check out his steam heating system. Working for contractors I replaced quite a few old sectional boilers but for the most part never had to leave the boiler room, looking at this building has really opened my eyes and sparked an obsession. After spending over the last month reading and researching I have a much better appreciation for why we do things and just how amazing the “dead men” were. I feel I was born a couple generations later than I should have.

Details of the system:

Building Age: Building built in 1889, but burned down, was rebuilt in 1911.
Original System: Coal Boiler, One Pipe Parallel Flow, Vapor or Vacuum… I’ll get into this later.
Current System: Hybrid? Zoned One pipe parallel flow, F&Ts at end of main lines, condensate receiver, surge tank, Radiators have air lines tied into the now dry return.
Current Boiler:
CRANE CO. 400 Series Gas Boiler Installed 1974
Natural Gas
Normal AGA Input: 1,400,000 BTU/Hour
Minimum AGA Output: 560,000 BTU/Hour
NET IBR Steam: 3501 Sq Feet
Cut In Pressure: .5 psi
Cut Out Pressure: 2 psi

The building’s about 5 hours away and I’ve been able to look at it on two separate trips. Each trip I’ve returned with plenty of homework. I hope I’m able to provide enough information to get a consensus on what to recommend the customer. I will do my best to keep the post updated but I’m a two man shop on a commercial project with liquidated damages so it may have to wait for the evenings before I get a chance to respond. I have a couple drawings and a few photos I will upload along with the post.

Let's start at the boiler room. In a large pit sits the boiler, behind and to the left a condensate receiver tank, back to the right a large red vessel that hammers every time the condensate receiver kicks on. In the front sits the boiler, the piping has 24” from the water line to the header, it has an equalizing line into the back of the boiler, the two top ports tie together in a way that I would have piped different but don’t see any real problems with the configuration. (I was unable to find a manual to verify against boiler manufacturer’s recommendations — Crane Boiler 8-400 —). The 4” header then offsets vertically another 16” or so, into another header that has (2) 3” branch lines to motorized control valves, it then reduces to 2” for the final motorized control valve. The (3) zones all make their way out and around the basement feeding various risers to the 2nd floor and radiators on the 1st floor. They’re all parallel flow, once they offset downstream the control valves. They end up together in a room in the middle of the basement. Each main has a main vent followed by an F&T trap, they all tie together into the now dry return, which I imagine used to be the “A Dimension” and a wet return.

The now dry return runs back into the boiler room and ties into the condensate receiver, out of the receiver condensate is pumped into a tee into the Hartford loop, the bottom of the line into the Hartford loop has a bullhead tee, one side a blowdown, and the other over to the bottom of a tank, the tank looks to be configured as such to increase the water capacity of the boiler. A steam line runs to the top of the tank. When first seeing the system I was very confused about the tanks function. — I have always installed boiler feed tanks — once I realized what it was doing and learned about “new” boilers holding less water, I think its a pretty cool component. (Photos attached)

Where the system really gets interesting to me are the “Air Lines”. I had heard of vacuum systems going through apprenticeship school, but the chapter was more or less skipped over and dismissed as “a thing of the past, that you’ll never see”. Without all the boiler room piping intact I don’t really know what this system once was, possibly a Paul system or something similar. The piping configuration is now all the air lines off the radiators, and all the main vents, tying together and connecting to the dry return just upstream of a check valve.

Walking the system I found two radiators that have regular air vents, one is a hoffman No 40, and the other is an adjustable. Initially I chalked this up as someone replacing vents and going with what’s more commonly found, but looking deeper I didn’t see any old holes through the floor… It is possible someone added these radiators at a later time and just piped them this way.. I can’t be 100% sure. It also got me thinking there may have been a reason for this, one appears to be the farthest radiator in the building from the boiler room. (Also these radiators are the only two in the building that weren't heating well, the one furthest from the boiler room I could hear condensate gurgling).

Food for thought… I know motorized control valves generally leave a lot to be desired in systems such as these, but could it be possible that when they were installed the designer had the idea of filling a zone with steam, getting all the air out (it seems to be vented very well) then the zone valve shuts, allowing for a naturally induced vacuum to form?


Do these old air lines fail? There doesn’t seem to be any steam leaking back into the dry return, but looking at the air line valves they don’t appear to have received any maintenance in a very long time.

Could this system still need the air lines? Or are they essentially just an air vent now?
— If the airline valves were acting as vents, I don’t believe the system could breathe, and would suspect a lot of steam hammer through out… which isn’t the case, condensate seems to move well.

Check valve on the inlet of the condensate receiver tank?
— I would think this would cause problems with flow from the F&T Traps to the condensate receiver tank, it essentially blocking the vent on the receiver tank? But it currently appears everything is working as it should…

What throttling valve to recommend?
— The condensate receiver discharges condensate into the system, this is causing hammering in the buffer tank, Dan shows a “Square head steam cock” in his book, I’m more familiar with globe valves would this work as well? Currently there's a ball valve which I don't want to recommend using for throttling.

Short cycling problem, the boiler turns on for about three minutes thirty seconds, then is off for about three minutes thirty seconds. This was timed on a pretty warm day around fifty degrees, my second trip the boiler seemed to be doing better, (I did not time it) it was about 9 degrees outside. — Most of the system is uninsulated, I’m sure it was asbestos and demo’d but not replaced, two mains are insulated, the branches and near boiler piping is not. I know the piping up to the motorized valves needs thick insulation to help combat the short cycling problem but is that the whole problem?…

Do the control valves need to be protected (installing drips/a F&T)?
— I didn’t hear any hammering when they were cycling.

Does anyone know of a good steam contractor on the western slope of Colorado I could recommend to my customer for a building like this?

Other than the short cycling issue, and hammering in the buffer tank, I don’t see anything jumping out as a real problem… Steam makes its way to the ends of the mains and radiators quickly. I would like to recommend ways address the issues and have a better understanding of how this particular system works, hope you guys can help!


  • KC_Jones
    KC_Jones Member Posts: 5,736
    The museum on here is your friend!

    That seems to be a Paul system. See this link for some information.


    I'm sure others with more knowledge and experience will chime in soon enough.
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
  • Big Ed_4
    Big Ed_4 Member Posts: 2,780
    KC ,,Would the tank be a vacuum tank ?
    I have enough experience to know , that I dont know it all
  • KC_Jones
    KC_Jones Member Posts: 5,736
    Big Ed_4 said:

    KC ,,Would the tank be a vacuum tank ?

    I am far from an expert on these, so I don't know. I know what those systems were in concept that's how I realized what it was from the pictures.
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
  • Steamhead
    Steamhead Member Posts: 16,821
    Air-line systems like the Paul worked by producing a vacuum that pulled the air from the radiators. You could do the same thing at the steam main ends using thermostatic traps hooked to vacuum lines, which would function as main vents. Most of these systems used steam-driven ejectors (jet pumps) to produce the vacuum.

    @Pumpguy is our resident vacuum-pump expert, hopefully he will see this.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Big Ed_4
  • Pumpguy
    Pumpguy Member Posts: 654
    Question: Are the radiators with the Paul air line valves fitted performing as they should, both heating and condensate draining?

    If the answer is yes, I guess the old adage IF IT AINT BROKE, DON'T FIX IT would apply.

    Does the red tank only connect to the Paul air lines? If yes, that would serve as a vacuum storage tank and a vacuum pump could be connected to it. The Paul valves should only pass air and close to steam. They can still be purchased but I believe are quite expensive. The red tank could act as a pressure storage tank, allowing the vacuum pump to run start - stop, controlled by a vacuum switch.

    The systems I deal with are usually much larger than this one and I use liquid ring vacuum pumps. These require a supply of seal water and they can be quite expensive.

    On the other hand, the vacuum pumps @Igorzhadanovsky uses are dry types, much lower in CFM air volume capacity and price too.

    If considering a vacuum pump, I would get @Igor's input before making any decisions.
    Dennis Pataki. Former Service Manager and Heating Pump Product Manager for Nash Engineering Company. Phone: 1-888 853 9963
    Website: www.nashjenningspumps.com

    The first step in solving any problem is TO IDENTIFY THE PROBLEM.
  • BenL
    BenL Member Posts: 4
    @Pumpguy the radiators with the airline valves are functioning as they should.

    The red tank has nothing to do with the vacuum system from what I can see, I believe its function is just as a buffer. I imagine the current boiler holds significantly less water than the original.

    Also, there is no vacuum pump in the system anymore.
    JUGHNE Member Posts: 11,058

    This is just a WAG on my part:

    So the condensate pump is controlled by it's own float....not by any control on the boiler?

    If so, does it then pump into the red tank....which has no pump...correct?
    And also pumps into the boiler thru the tee at the Hartford Loop?

    Then is there a steam equalizer line connect to the top of the red tank?

    If so then the red tank is an accumulator/reservoir for condensate.
    This gives more water capacity...larger boiler...but no fire under that part of it.

    I have used a plug type valve (actually they are repurposed gas stops) to restrict cond pump output. Even have tied a recirculation line with another plug valve, back into the tank to cut the flow down.

    Is that cond pump vented for air removal from the F&T's?

    Usually there is a vent pipe going up high and also an over flow pipe.

    Is there some form of auto water fill on the boiler?
  • BenL
    BenL Member Posts: 4
    @JUGHNE This is the same conclusion I came up with, definitely no communication from the LWCO to the condensate receiver. I really like the idea of the recirc to cut flow down if the plug valve doesn't work.

    The Condensate pump is vented but there's a check valve in-between the F&Ts and the receiver tank, I would think this may cause problems but condensate seems to be flowing fine into the tank. There are no vacuum breakers or air vents down stream the F&Ts either.

    Also there's no auto fill to the boiler just domestic water isolated by a back flow and ball valve.
  • Mad Dog_2
    Mad Dog_2 Member Posts: 6,882
    Looks like an exciting job. I wish I was in there figuring it out with you.  Where is this job?   Mad Dog
  • BenL
    BenL Member Posts: 4
    @Mad Dog_2 PM Sent