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Please help with main vent sizing

I am working on a 2 pipe steam system that the main vent sizes seem very small for the size of the system. It is a Weil McLain 580 oil fired at 165 psi 3.25. There are two mains both 4". One is 94' long the other is 75' long both vented with single hoffman 75's. does that seem small to you. This thing has been drinking oil and I'm hoping this is a big part of the problem. Thank you so much in advance.

Comments

  • BobC
    BobC Member Posts: 5,228
    Need a lot more

    If those are really 4" pipe then the mains contain about 7.5 cu ft of air each. The 75 is rated at 0.5cfm so it will take at least 15 minutes for the air to leave. I would add 4 or 5 Gorton #2's (6 or 7 would be nice) to each of those mains but keep the 75's as well because they will continue to vent after the Gortons all close.



    Just get yourself some T's and nipples and have at it, remember the Gortons use a 1/2" thread while the Hoffman is a 3/4" so you will need some reducers for the Gortons.



    Bob
    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Steamhead
    Steamhead Member Posts: 14,837
    Those Hoffmans are basically toys

    when installed on those mains. The longer main contains roughly 7.5 cubic feet of air, so it will need 7 Gorton #2 vents. The shorter one contains 6 cubic feet so 5 Gorton #2 vents and one of the Hoffmans should bring it into line with the longer one. You want the steam to reach the ends of both mains quickly and at about the same time.



    Note that you might need to increase the size of the vents' steam main connection to take full advantage of this venting setup. I'd suggest at least a 1" pipe coming off each steam main. If all you have is 3/4", you can add another 3/4" connection to get the needed pipe capacity.  Remember, we're venting at 1 or 2 ounces so piping resistance is a factor.
    All Steamed Up, Inc.
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • SWEI
    SWEI Member Posts: 7,356
    FIve Gorton #2s

    isn't this a good candidate for a thermostatic trap?
  • Steamhead
    Steamhead Member Posts: 14,837
    In these sizes

    you'd still need multiple traps, unless you went with one of the big Nicholsons which are quite expensive- possibly more than a set of Gorton #2s, and you'd need two of them. Also, in some cases the Gortons are more readily available- for example, I don't even know who in my area would carry the Monash traps JStar has used. But obviously someone in Joisey does.
    All Steamed Up, Inc.
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • BobC
    BobC Member Posts: 5,228
    edited December 2013
    A few now, more later

    I was wondering just how much capacity a 3/4" pipe would have. According to the venting capacity chart a 1/2" pipe would be good for about 2.5 Gorton #2's so since a 3/4" pipe has almost twice the area of a 1/2" pipe perhaps we could put 4ea Gorton #2's on a single 3/4" tapping - I would leave the Hoffman in a addition to the Gortons.



    4ea Gorton #2's should be a lot better than a single #75 and you could add a second 3/4" tapping later if you wanted to optimize things. This should substantially improve things without having to mess with the mains piping right now.



    Bob
    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Mep4888
    Mep4888 Member Posts: 4
    vents

    Thanks for all the help guys, I am a heating contractor, but this is my first step into a serious steam system. I took the job so I could educate myself. They are 4" mains, it is a three story masonic lodge. Would the under size vent cause them to use 400 gal of oil in 12 days? Why would this system ever be set up with such a small vent? I've been through the oil burner and pressuretrol all is running okay (1/2 lb with 1lb dif). should I worry about any pipe hammer with the steam moving that fast with the gorton vents?
  • BobC
    BobC Member Posts: 5,228
    Large main vents help save money

    Under venting means it is taking more time to fill the mains, and hence the radiators, with steam. For efficiency you want to fill the mains fast and then feed the radiators slower for good equal steam distribution. If faster venting will fill those mains and radiators ten minutes faster every time the system starts to make steam that is going to save fuel.



    When the system was installed it was likely coal fired, coal fired steam boilers are on all the time so slow venting didn't really matter. Gas and oil fired boilers turn on and off many times a day so it's important to get the steam from the boiler up to the radiators quickly, fast venting is one way to do that.



    As long as everything is properly pitched and sized, getting steam to the radiators quickly will not cause water hammer. Allowing the radiators to vent to fast can cause problems because it is possible to produce condensate to quickly. All the piping you can reach should be insulated, especially the mains and near boiler piping.



    Aside from the high fuel usage how does the system perform? What size is the boiler and what is the connected EDR? If you think there might be a problem with the boiler or piping post some pictures so the pro's can give you their opinions about what might have to be changed.



    Bob
    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Mep4888
    Mep4888 Member Posts: 4
    vent

    The system is need of maintenance, I replaced all the steam traps on the third floor just because no one could remember when they were last maintained, probably 10 years earlier, some of them came out in two pieces. One of the Hoffman main vents has failed and does not seal up anymore so I don't think the burner satisfies. the air runs out continuously, I just found it today. so I ordered the gorton vents you recommended and will be installing them Saturday morning. The main is insulated about 75%. the other two floors I think I should replace all those steam traps then everything is the same age. the boiler was installed about 10 years ago by a reputable company that put in new f & t traps also, I am surprised they didn't resize the main vents also, but then again they are also in the fuel selling business. Thanks again
  • Steamhead
    Steamhead Member Posts: 14,837
    400 gallons in 12 days?

    That sounds high. The inadequate venting is certainly a problem, but it may not be THE problem.



    I'd check the following:



    Oil tank, to see if it's leaking. If it's underground, assume it's leaking unless and until a professional tank company says otherwise.



    Boiler fire side- if the oil company has been servicing the boiler, assume they've just been ragging and tagging until proven otherwise. Soot and sulfur are great insulators.



    Boiler water condition- dirty or oily water will impair steam production, which would take extra fuel to overcome.



    By all means do the vents and traps first. Also consider switching that boiler to gas- W-M does supply gas burners for it.



    Let us know how you make out!
    All Steamed Up, Inc.
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • SWEI
    SWEI Member Posts: 7,356
    What's the capacity of a standard radiator trap

    Like say a Hoffman 17C, as compared with a Gorton #2?
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