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Retrofit Options for Paul 3-Pipe Steam System

SMATA Member Posts: 2
I have a building that I believe was originally a Paul, 3-Pipe system with valved supply and return lines on the radiators, and an additional air line coming from the vent taps. The building has since been converted mostly to a 2-pipe, vented system with all radiators having direct air vents now. However, the building also includes a number of 1-pipe radiators and the possible configurations present are:

1. 1-pipe radiator with air vent
2. 2-pipe radiator with air vent and no trap
3. 2-pipe radiator with air vent and with trap

Given the diverse configurations present, including having both dedicated return lines, as well as having condensate draining back into the supply lines from the 1-pipe radiators, what are the best options for retrofitting this system?

The residents don't seem to have a problem with water hammer. Upon inspection, almost all of the traps on the radiators that had them failed a differential temperature test.

Typical 1-pipe radiator:

Typical 2-pipe radiator with trap:

Typical 2-pipe radiator without trap:


    EBEBRATT-Ed Member Posts: 13,797
    Well for starters you can't mix two pipe radiators with traps and two pipe radiators without traps on the same system if the returns are mixed together........That would cause all the traps to fail.

    I wold make all the two pipe radiators with traps. The one pipers can live with the two pipe trapped radiators if it's piped right. You may need loop seals (or traps) between the 1 pipe and the two pipe returns ..........depends on how they are piped
  • MilanD
    MilanD Member Posts: 1,160
    Retrofitting to what?

    Seems like someone has taken the time in the past to create a hybrid system. If it works, just make sure the components for each of the systems are functioning properly. Treat them each as a separate system within one building. I'm assuming all are connected to one boiler and/or district steam.

    Look at main venting and rad venting on 1-pipe.

    Check crossover traps and vents on mains and check traps on 2-pipe with rad traps.

    Check actual vents on the vented 2-pipe.

  • MilanD
    MilanD Member Posts: 1,160
    edited February 2020
    Btw, if they are not separated, and as Ed suggests, mixed so that vented 2-pipe steam can make it to the back of trapped 2-pipe radiators, then, all that will need to be addressed. But given it all works, my bet would be a well thought-out hybrid system.
    SMATA Member Posts: 2
    Ed - Yes, this is the problem, the radiators without traps allow steam to blow through into the return, among other things, using far more fuel than is necessary. What would be a correct piping correct configuration that would allow 1-P radiators to drain without adversely affecting other radiators downstream?

    MilanD - Primarily, the goal of the retrofit is to most expeditiously fix the wild inefficiency of the current system. The current heating index and fuel usage is very high. How would you treat both systems as separate when they are connected by common supply lines? Shouldn't the issue of the condensate draining back into the supply lines be addressed? Either by removing the 1-p radiators or by installed some sort of bleed line?
  • MilanD
    MilanD Member Posts: 1,160
    edited February 2020
    I went with the assumption that the system was a propper hybrid with separate returns for various systems presented (individually dripped vented 2-pipe rads, properly trapped and vented returns on the trapped 2-pipe rads).

    If indeed it is a "Fankensystem" and a product of butchering, I'd follow Ed's reco, unless you have an economical way to gather all the trapped 2-pipe rads' returns in the basement and create a properly vented dry return for them, or properly drip or p-trap all the improperly dripped reruns on the vented 2-pipe rads. From your post it sounds both are present.

    This would be situation specific and I don't know your situatuon: number of affected rads and the condition and ease of finding all the 2-pipe trapped rad returns in the basement, or the number and ease of adding traps on each of 2-pipe vented rads, etc...

    Sounds like a head-scratcher for sure!
  • MilanD
    MilanD Member Posts: 1,160
    One last thought:

    One pipe rad additions won't give you trouble if piped and vented correctly (or added later) IF their load does not exceed the capacity of the main with other rads already attached. So, this can be an issue, possibly.

    Returns on 2-pipe vented should not be terminating in the supply main, but either have individual drips under water line, or some kind of p-trapping before returning back to the main for condensate return.

    All rads with individual traps need to go to a dedicated return line, with one main vent or a cross-over and a vent before becoming wet. Also, if one rad trap on these fails and is not replaced, it will eventually make all other traps fail and affect all venting. It will affect venting on a cross-over or without it, as it will not allow for venting with steam present where not supposed to be and cutting off air elimination at the vent.
  • Pumpguy
    Pumpguy Member Posts: 612
    I don't see stated what this system's operating steam pressure is.

    If you can control the flow of steam into the radiators (frequently done with orifices at the radiation's steam inlet connection, or lowered system steam pressure), so the volume of steam admitted is less than the condensing capacity of the radiator, you should be able to get by without needing steam traps.

    The problem is, orifices are dumb. They don't modulate to account for varying loads, so successful operation under one set of conditions may not work for different conditions.
    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.
    EBEBRATT-Ed Member Posts: 13,797
    Depends on if the 1 pipers are all in 1 location or intermixed with the two pipe radiators.

    What I have done on 1 job where I had this issue I had a steam main that fed a bunch of one pipers. At the end of the 1 pipe main I dropped that main to the floor and then brought it back up creating a "loop seal" and tied it into a return that had 2 pipe rads with traps on them.

    The loop seal filling with water stopped the steam from the 1 pipe main from getting into the returns.

    Every situation is different. Hard to say without seeing it but 1 way or another I am sure there is a way out of it.
  • AMservices
    AMservices Member Posts: 605
    I'm going to say the system was originally all air vented, No traps.
    You should keep it that way. Nice and easy.
  • dopey27177
    dopey27177 Member Posts: 887
    from your assesment in the first statements about the steam system I do not think Paul visited your building.

    I believe the third pipe originally was for a cross over trap that vented air towards the boiler room.

    The third pipe could have been piped to the chimney, to a condensate tank or just to the outdoor atmosphere.

    Looking at the radiator (the one that looks like it is an **** warmer the inlet and outlet pipe appear to be the same size. If this is the case the building heating system heated on vapor pressure.

    I would lower the steam pressure to 1/2 psi max with a 1/4 psi differential and see hoe everything operates.

    Low psi two pipe steam systems with out steam traps operated at 1 psi cutout and 1/2 psi cut in. On those systems the return pipe from the radiator was one or two sizes smaller than the inlet steam supply to the radiator.

    Some where along the line you may have to adjust something because of the one pipe steam rads.

    Pictures of how the one pipers tie into the risers would be helpful if problems occur at the lowest operating pressures.

  • jumper
    jumper Member Posts: 2,121
    MilanD said:

    One last thought:

    One pipe rad additions won't give you trouble if piped and vented correctly (or added later) IF their load does not exceed the capacity of the main with other rads already attached. So, this can be an issue, possibly.

    Piped correctly is the rub. Risers yes, long runs (branches?) are trouble.