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Vacuum Pump control on a one-pipe steam radiator system

Hello.

I have a circa 1900 four-story residential building that has a one-pipe steam radiator system. There are approximately 80 units in the building and each unit has 3 - 6 radiators in them depending on square footage.

This is my question: How should the vacuum pump be controlled? I have a PSIG gauge on the vacuum pump so I can easily determine IWC or IHg.

Currently, I am turning the vacuum pump on when I enable the boiler. The combustion air damper takes a minute or so to open and the boiler commences with its startup sequence once the combustion air damper is proven open. The gas valve begins to open and the burner fires approximately three minutes after the vacuum pump is commanded on.

Depending on how long the boiler has been sitting idol, my vacuum pump gauge reads anywhere between 0.1 and 1 PSIG when the vacuum pump first turns on.

How should I control the vacuum pump so that I get a nice differential pressure for good steam flow?
If I run the vacuum pump too long and all of the thermostatic condensate valves on the radiators close off because the steam is present in the radiator, do I risk pumping steam from the one-pipe system back into the vacuum pump?

Please feel free to fill in any blanks or to ask if me if you feel that I am leaving any pertinent information out of my thread.

Thank you.

Comments

  • AMservices
    AMservices Member Posts: 610
    Do you have vacuum lines to each radiator?
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,297
    Most one pipe systems do not have a vacuum pump. Need some radiator pictures, boiler piping pictures and vacuum pump pictures to assess.

    two pipe systems are common with a vacuum pump
  • Pumpguy
    Pumpguy Member Posts: 627
    If you have separate air lines running down to the vacuum pump, then most likely you have a One Pipe Air Line Paul System.

    Attached is a diagram of this system with description of how it works.

    While the normal operating vacuum on a 2 pipe vacuum return system is OFF @ 8" Hg. vacuum, and back ON @ 3" Hg. vacuum, I have not found any such prescribed settings for a Paul system. I have been advised that the above settings are a good starting point, which may be changed as your experience dictates.

    If your vacuum pump is not set up to run start - stop, controlled by a vacuum switch, I would recommend installed a spring loaded vacuum relief valve, AKA vacuum breaker, to limit the maximum system vacuum.

    One such spring loaded vacuum relief valve is a 3/4" Hoffman # 62. These come from the factory set to break at around 2" Hg. vacuum, so to maintain a higher vacuum, you will need to tighten up on the adjusting springs to raise the vacuum break point.

    Could you tell or show us what type of vacuum pump is applied to your system?
    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.
  • jumper
    jumper Member Posts: 2,206
    It's more complicated than simple pressure. Total pressure is the sum of steam pressure plus air pressure. For example 0 psig equals no air if water is at 212°. Then you don't want vacuum pump on.

    Unless there's vacuum lines to each radiator you can't hasten steam circulation with mechanical means simply because theirs no circuit. But steam moves faster when there is no air in the way. So you want to evacuate air before the boiler fires.Theoretically you would run the vacuum pump until pressure approaches vapor pressure of water in boiler. Assuming that all vents have been plugged. Otherwise air goes in as fast as you suck it out.
  • ppecoraro
    ppecoraro Member Posts: 6
    It has been described as a Mills-Paul system.
    Yes, I have air line valves but many of them are failed and in the process of being replaced.
  • ppecoraro
    ppecoraro Member Posts: 6

    Do you have vacuum lines to each radiator?

    Yes. With airline valves. It is a Mills-Paul overhead system.
  • ppecoraro
    ppecoraro Member Posts: 6

    Most one pipe systems do not have a vacuum pump. Need some radiator pictures, boiler piping pictures and vacuum pump pictures to assess.

    two pipe systems are common with a vacuum pump

    It is a one pipe system with airline valves. It is a Mills-Paul overhead system.
  • ppecoraro
    ppecoraro Member Posts: 6
    jumper said:

    It's more complicated than simple pressure. Total pressure is the sum of steam pressure plus air pressure. For example 0 psig equals no air if water is at 212°. Then you don't want vacuum pump on.

    Unless there's vacuum lines to each radiator you can't hasten steam circulation with mechanical means simply because theirs no circuit. But steam moves faster when there is no air in the way. So you want to evacuate air before the boiler fires.Theoretically you would run the vacuum pump until pressure approaches vapor pressure of water in boiler. Assuming that all vents have been plugged. Otherwise air goes in as fast as you suck it out.

    It is a Mills-Paul overhead system with thermostatic airline valves tied into the vacuum system.
  • ppecoraro
    ppecoraro Member Posts: 6
    Pumpguy said:

    If you have separate air lines running down to the vacuum pump, then most likely you have a One Pipe Air Line Paul System.

    Attached is a diagram of this system with description of how it works.

    While the normal operating vacuum on a 2 pipe vacuum return system is OFF @ 8" Hg. vacuum, and back ON @ 3" Hg. vacuum, I have not found any such prescribed settings for a Paul system. I have been advised that the above settings are a good starting point, which may be changed as your experience dictates.

    If your vacuum pump is not set up to run start - stop, controlled by a vacuum switch, I would recommend installed a spring loaded vacuum relief valve, AKA vacuum breaker, to limit the maximum system vacuum.

    One such spring loaded vacuum relief valve is a 3/4" Hoffman # 62. These come from the factory set to break at around 2" Hg. vacuum, so to maintain a higher vacuum, you will need to tighten up on the adjusting springs to raise the vacuum break point.

    Could you tell or show us what type of vacuum pump is applied to your system?

    It is a Mills-Paul overhead system with thermostatic airline valves tied into the vacuum system as you show. A good portion of the airline valves have failed open so I do not want to introduce steam/condensate into the airline. But with the vacuum pump turned off, I feel that I do not get good control in the condominiums. They are accepting bids to fix the airline valves. When that work is complete, then I would like to ensure that I am controlling the vacuum pump properly. With this knowledge, do you still stand by the OFF @ 8" Hg. vacuum, and back ON @ 3" Hg. vacuum?
  • AMservices
    AMservices Member Posts: 610
    @ppecoraro where are you located? And Can I see pictures of where the old Paul ejector system was?
    8hg is plenty.
    @izhadano Made his system work very similar to the pauls system. When he began testing he was using the pauls vent and found them to be unreliable.
    It is possible to get around using the pauls vent.
    There is a much more affordable option for Vacuum pumps.
  • jumper
    jumper Member Posts: 2,206
    Them's a lot of pumps. Overhead distribution is the best. What do you mean by "thermostatic condensate valves"? There are vacuum generators that are not harmed by steam. But it is wasteful to evacuate steam.