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Main Pipe Pitch

DNW
DNW Member Posts: 20
I have a 2-pipe Trane Vapor System.  I understand from reviewing some of the posts that mains should be pitched at 1 in / 10 ft for counterflow, and 1 in / 20 ft for parallel flow (minimums). 



I need to raise some sagging main pipes in my crawl space (where hangers have been torn off).  I've attached a general layout of my main pipes.  The steam heads outbound from the boiler in a 3-in main pipe, then distributes into two loops to the 19 convectors before getting back to the boiler.



Is it likely that the outbound 3-in main is counterflow, and should be pitched back to the boiler, and the two distribution loops are parallel flow, pitching down in the same direction as the steam flow?



Thanks!

Comments

  • Rod
    Rod Posts: 2,067
    Main Pitch

    One of the pros who is familiar with Trane systems could answer this better than I could.

    I would guess the system is completely parallel flow. The first thought that comes to mind is would be to check the 3 inch main with a water hose level. That way you could tell if the boiler end or the connection to loops was higher which would help determine if it was designed as a parallel or counterflow.

    Just a thought.

    - Rod
  • DNW
    DNW Member Posts: 20
    Water Level

    ... sounds like a great idea.  I'll see if I can figure out how to do it.  The main is about 45 ft long, all in crawl space with 6 in to 2 ft clearance!  And, I'll be on my own.

    Darrel
  • Jamie Hall
    Jamie Hall Member Posts: 20,500
    It actually doesn't matter that much...

    The terms parallel flow and counterflow are really more applicable to systems which don't have returns of any kind.  In a vapour system, there will be dry returns -- and usually wet returns as well.



    The whole idea is that the air from the radiators will go to the dry return, and will be vented, usually at the boiler where the dry returns come together and drop.  Any air in the steam mains will either be vented with main vents oor vented into the dry returns by crossover traps.  The condensate from the radiators may go into a dry return, and then flow either back to the boiler (if the return is pitched that way) or to a drip to a wet return (if the dry return is pitched that way instead).  The essential thing, then, is that condensate -- from whatever source -- either goes back to the boiler or finds its way to a drip to a wet return.  So long as that happens, it really doesn't matter which way either the dry returns or the steam mains pitch.  What DOES matter is that the pitch be continuous and even, either to the boiler or a drip.



    So what you are really looking for is do the pipes slope evenly?  And do the slope to either the boiler or a drip?



    It's not common, by the way, for the mains to come all the way back around as yours appear to do.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • DNW
    DNW Member Posts: 20
    edited January 2012
    Main Pipe Pitch

    Thanks for the reply, Jamie.  On this system, the 3" main steam line goes from the boiler straight under the spine of the house - about 45 ft.  At the end, the line T-s into left and right loops, which return to the boiler.  All the convectors feed from these two loops.  The convectors vent / drain through traps into condensate return loops which run alongside the steam mains back to the boiler (Trane Direct Return Trap).  The condensate returns are above the waterline (about 50") - does this make them "dry" returns?



    The two steam loops and the two condensate loops are vented when they return near the boiler. 



    I'm trying to solve a BAD steam hammer issue.  When I finally got up under the 3" main, I saw that it had at least two loose hangers, and was sagging about 2 inches (or more).  I want to lift this back up, and would like to make sure it's pitched in the right direction.  It looks like several hangers are missing on the distribution loops, as well.  I can tell that these loops DO slope downward WITH the steam flow (parallel).

    The 3" main is elevated 79" above the floor where it heads out, and the two loops are at 71" and 72" where they return.  Assuming a 1/20 pitch for parallel flow, I guess it's possible ALL the mains are pitched down (7" drop would cover 140 ft of pipe, which is about what there is in each loop - including the 3" main).



    After I get the mains strapped up, I'll insulate all the steam pipes. 



    Thanks to everybody for their assistance.  I've been unable to find any knowledgeable professional help around here (NC).  I guess they're too busy putting in heat pumps!



    Darrel
  • Jamie Hall
    Jamie Hall Member Posts: 20,500
    Well now...

    that sag would create a racket...



    And loose hangers can make sags where you least expect them!



    Those returns are indeed dry returns -- just what you would expect with a Trane. It does sound as though you'll be able to get everthing to go around to the boiler, which is good.



    The only thing I would really suggest here is: don't trust the floor.  I would strongly recommend using -- at the very least -- a really good 4 foot level.  Even better, if you can get hold of it and there aren't too many obstructions, would be to establish a level plane with one of those rotating laser contraptions, and systematically measure up from that -- and use the level in addition.  Floors in basements have a way of being... untrustworthy, shall we say!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Hap_Hazzard
    Hap_Hazzard Member Posts: 2,787
    Hanging pipe

    When hanging schedule 40 pipe for vapor service, you should have a hanger at least every 15 feet for 3" pipe and 14 feet for 2 1/2" and within one foot of any fixtures. Use clamp or clevis type hangers, not wire or perforated strapping. Hangers should be hung with 1/2" threaded rod.



    crash2009 posted this picture a few weeks ago: http://www.heatinghelp.com/images/posts/10519/resize_PICT0339.JPG



    I don't know where to get these, but if I hadn't just finished re-hanging my pipes I'd really want to find out.
    Just another DIYer | King of Prussia, PA
    1983(?) Peerless G-561-W-S | 3" drop header, CG400-1090, VXT-24
  • Hap_Hazzard
    Hap_Hazzard Member Posts: 2,787
    edited January 2012
    Level

    The level I use is a 12" bridge level. It has magnets on the base so you can hang it from a pipe while you're adjusting the hangers, and, in addition to the horizontal and vertical bubble vials for checking level and plumb, it also has a rotating one with a scale you can set by degree--but since we're dealing with < 1 degree here, you can just set it to level on a pipe whose pitch you know is correct.
    Just another DIYer | King of Prussia, PA
    1983(?) Peerless G-561-W-S | 3" drop header, CG400-1090, VXT-24
  • DNW
    DNW Member Posts: 20
    Too Warm to Test

    Thanks for all the suggestions!  I replaced a few hangers that had been torn down by the A/C yahoos (20 - 30 yrs ago), and added a couple more.  I used a magnetic level, with pitch indicators.  The shallowest pitch it has is 1/8"/ft, so I pitched the pipes about midway between level and the 1/8 mark. 



    It's been in the 50s and 60s since I did all this, though, so I haven't been able to tell if the hammering is improved.



    DW
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