Two pipe question

JK_3

I am helping a friend that is working on a two pipe system. All of the rads are top feed with 3/4" and 1/2" steam traps on the returns. At the ends of the 2" steam mains are 2" x 3/4" tees that are plugged (but look like they should have main vents) and then loop back to a 1 1/4" return picking up each of the riser returns on the way back to the boiler room. The risers are 1 1/2 " and the return risers are 3/4" except for the risers with out rads( bathrooms and kitchens) are 2' with 1' returns and 3/4" steam traps at the bottom.The return mains  are over head (about 1 foot below the mains). At the tee where the returns meet to drop down there is a main vent (but it looks like it may have been added later). I am just looking for some input as to what may have supposed to have been and I cant help but thinking that the steam is also filling the return risers (because there are no traps where the steam main loops back to become the return main) and that this would cause problems like steam coming in the return side and flashing the condensate. I am looking forward to any input.

gerry gill

seems to me that

there should be F&T traps at the ends of the mains..can you post any pictures?

Jamie Hall

Either...

the F&Ts that Gerry mentions, or possible crossover traps (like radiator traps) -- but something to keep steam out of the return is necessary.  Might it be possible to post a picture or two of the arrangement at the ends of the steam mains, where those 2x3/4 T's are?  I almost wonder if there was something there, once upon a time... like a crossover trap.

JK_3

But what was there ?

I will try posting some pics later today. One of the things that is troubling me about this is that it doesnt look like any thing has been removed from the end of the mains but I am not sure yet as the last time I was there they were still covered. They have been uncovered for me to see now and I am going back today for a beter look and take some pics. I am not sure I would want to put F&T traps because we are still trying to get the pressure under control.

What are crossover traps. How do they work? I was thinking something similar to a steam trap but again I would like to understand how this system was supposed to work when it was installed. I will post some pics later today and I appreciate any input to try and figure this out.

Jamie Hall

Crossover traps

were used on a variety of vapour steam systems.  They are exactly like radiator traps (in fact, they are radiator traps -- usually 3/4 inch).  They are piped as follows, usually from a T or elbow -- straight up on a nipple, then 90 over to the inlet to the trap.  Then down from the outlet of the trap to the dry return, which is usually a few inches to a foot or so below the steam main.



The idea is that while air is being pushed around, the traps are open and the air goes out of the steam main and into the dry return.  It then goes back down the dry return to wherever the return drops (usually right at the boiler) where there is a main vent (in some systems) or some other contraption to let the air out.



Note that they don't do condensate.  That is handled by a drip to a wet return.

clammy

water seal

Sounds like this sytem either at one time had a wet return which the steam main dripped into or a u bend water seal at the end of the main which dropped down and looped back up into and  then tied into the dry retun .I have ran into and seen this piping orangement  .If it is a 2 pipe system those 2 x 3/4 tees most likly had cross over trap instead of air vents but i have seen it both ways  .If you build a water seal please install a vapor stat other wise you will push the water out of the seal unless you make your loop over 30 inches mimiun and remenber to fill the seal loop prior to starting the boiler other wise steam will get into that dry return ,If you install a f and t at the end of the main make sure you do not have any steam pressure in the dry return other wise it might start stacking up condensate and other issues will arise.Other thing to take alook at is does each dry return tie together above or below the water line .I always seperate them add a tee for  air vents and drop them seperatly into a wet return .Even though in some older system it would have tied into a single main air elimator but these system where usually originally coal fired and fired for many hours unlike modern day equiptment which is electronically controlled by thermostats and pressuretrolls.Dans lost art has all this stuff in it if you don't own a copy or two get one well worth the price a hunderd times over peace and good luck clammy