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What should I do, loop seal or F&T'S




Weil-mclain 580 on a 2 pipe Trane system. I've been servicing this boiler for approximately 4 years. This year the customer started getting water hammer and springing leaks around the swing checks in the old wet return (3rd pic down). 
Before the current owner bought the house one of the previous contractors installed a boiler feed system. That being the case and understanding the purpose of the swing checks, I figured it didn't make sense to put a 2" swing check back in so I straight piped it. 
I wasn't sure how easily it was going to come out so I warned the customer that I may end up having to replace more than just where the leak is. Turned out that I was able to cut out the swing check and remove the nipples to fit a union back in (1st pic). 
2 weeks later the customer said they have another leak, this time in the middle of the pipe that comes off the bottom of the boiler return trap and now there's water hammer in the area that I worked on. 
In the 2nd picture down you will see the main air vents. 2 hoffman #75 on the dry return, to the right of the BRT. Then there's (2) 1" lines that come from the end of the 2 steam mains that goes to the  2 #75 to the left of the BRT.
2 years ago I replaced every radiator steam trap. No water hammer in the radiators or the dry return. There's no kind of trap for the steam main vent line. It starts hammering after about an hour into the heat cycle. Boiler builds 1.5 psi. 
What I want to do is replace all the old pipe in the wet return. Either add a loop seal to the main vent line, or separate the (2) 1" lines and put 3/4" F&T's with air vets. 
Thought? Concerns? 

And yes I know with this system it shouldn't be running more then 16 ounces of pressure. I'm trying to get the owner to buy a vapor stat as well. 

Thank you in advance. 

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 23,270
    You are, I think, on the right track. What is the pressure when the trouble starts? What may be happening is that the checks were a hopeful effort to keep water from backing out of the boiler under pressure into the dry returns -- which will be at atmospheric pressure or very near it. What is the vertical dimension between the boiler water line and the lowest point of the dry returns? At 1.5 psi, you will need that to be 42 inches...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • AMservices
    AMservices Member Posts: 610
    There's a boiler feed tank. The blue lines are the water level. The red line is the end of the steam main. 
    I either want to make that a loop seal or put F&T's.
    Whats the better option?

  • Jamie Hall
    Jamie Hall Member Posts: 23,270
    There is a boiler feed tank? Vented? Then you will need an F&T.

    But... why is there a feed tank in the first place?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Steamhead
    Steamhead Member Posts: 16,821

    There is a boiler feed tank? Vented? Then you will need an F&T.

    But... why is there a feed tank in the first place?

    This. A LOT of boiler feed tanks are unnecessary. Where is this job located?
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • AMservices
    AMservices Member Posts: 610
    Because some contractor (not me) told the previous owner they needed one. 

    So should I do away with the #75 vents and let the air vent through the tank? 
  • Jamie Hall
    Jamie Hall Member Posts: 23,270
    No -- the problem isn't with where the vent is located, it's that the wet returns feeding the tank don't have boiler pressure on them. Without an F&T, then, any steam reaching a pipe connected to a wet return will blow through into the tank. Not what you want.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    AMservices
  • AMservices
    AMservices Member Posts: 610
    F&t it is then.
    Thank you @Jamie Hall
    @Steamhead jobs in mass. The first time I looked at this system I told the customer that they didn't need the tank. But they had just replaced the motor before we met and wasn't hearing anything about restoring it to a gravity return. 
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,510
    They may be running the pressure too high for a loop seal. I like loops seals. As long as they don't plug they are trouble free
  • Jamie Hall
    Jamie Hall Member Posts: 23,270

    They may be running the pressure too high for a loop seal. I like loops seals. As long as they don't plug they are trouble free

    So do I. But if someone got creative and put in a feedwater tank, one is pretty much out of luck at least on seals that involve a wet return.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Steamhead
    Steamhead Member Posts: 16,821
    edited January 2022
    @AMservices , your F&T traps should go on the drips at the ends of the steam mains. Dan covers this almost at the end of chapter 10 of "Lost Art"- he's talking about one-pipe systems at that point, but the placement on steam mains whose drips form "A" rather than "B" dimensions is the same.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting