connecting dry returns above water line

STEAM DOCTOR

thanks for the great site. i view this site on a regular basis and the info that i have learned is immeasurable. I'm a plumber who has recently entered into the steam buiseness. on a number of jobs i have noticed that the dry returns are connected above the water line. I'm assuming that this is inadvisable because in essence this creates a continuous steam loop which would result in steam entering both sides of the loop and would equalize the steam pressure resulting in the slow movement of steam(sorry for the run on sentence). please correct me if I'm wrong and please enlighten me(and everyone else) with any relevant info on this topic. THANKS 

PS i have lost art(worth its weight in gold) and i dont recall this topic being discussed. 

Nick_C

Water Hammer

The biggest issue this causes is potential water hammer as the steam runs up the condensate line.  I haven't seen it slow down venting, though.

Jamie Hall

Not sure I quite follow

Dry returns connected above the water line -- to what?  If they are direct connected to a steam main above the water line, steam will bring the dry return up to the same pressure as the main, and it will be very hard (to put it mildly) for steam to get to the radiators -- unless they are vented.  On the other hand, if they are connected to each other, no problem of course.  And if they are connected to the steam main through a trap, there isn't any problem either (in fact, a lot of vapour systems were designed to be this way).



So... can you clarify to what they are connected, and how?

jpf321

me thinks...

i believe the situation here is that there are 2 mains that branch from the header and then run around the basement loop and are then joined by a dry return .... my guess is this is b/c someone forgot to attend to the waterline when a boiler was replaced .. this would be the case in my situation if the water line was lowered on my new boiler .. (see pic) I have a horizontal join which is below the NWL. i think the original poster is stating that he has this join above NWL.

RAF

Photo

If this is the basement floor and the line on the bottom is running back to the boiler , well sure looks like a wet return to me. Jamie?

jpf321

yes mine is wet ..

i was trying to depict a situation that the original poster maybe running into where the water line is BELOW that horizontal join. I am not the original poster. 

Jamie Hall

Indeed...

jpf's is the classic, RAF -- when things are joined depending on a water seal from a water line at a particular elevation, then coming back wet.  And it is a classic, because unless someone looks all over the basement when they put in the new boiler, they are likely to put the water line too low, and what was a water seal isn't anymore.  Oops...



But I still don't know exactly what the original poster's configuration is.  If jpf's surmise is correct -- and I wouldn't be a bit surprised -- it needs to be fixed.  Trap, false water line, something...

STEAM DOCTOR

sorry about the delay

I'm the original poster. the scenario is as jpf described. there are two mains that circle the basement. both mains return to the boiler room as dry returns. the two returns join at a T above the water line and then drop below the water line using a single vertical pipe. I'm assuming that the right way to pipe is to have each return independently drop below the water line and to then join.

Jamie Hall

Not necessary

There is no problem with two returns joining above the water line, so long as they drop below the water line before they have a chance to see steam.  At what point, though, and how do these turn into returns from being steam lines?  I'm still confused, I guess.  Or are they, in fact, just steam lines which go around the basement and then finally drip into the wet return to the boiler?  Almost sounds as though that's what you are talking about?

Unknown

Seperate Drops

I think I'd drop them down individually into the wet return with a vent on each before they turned down.

 That way you can be sure that there won't be "cross balancing" between the the returns. There was a two pipe system on here a few weeks back that had the return from the Steam main (wet return -no F&T trap) and the return from the "Dry Return" Main joined above the water line before the wet return and this was causing big problems as the steam main was was short circuiting to the dry return main.

- Rod

jpf321

i'm less confused....

because i have what i believe to be the same scenario just a few feet from me .. you have a few choices:



1) raise the water line to seal the horizontal join, presumably using a "false-water-line"

2) lower the horizontal join to below the waterline

3) an F&T trap on each drop before the horizontal join



some other non-conventional options may include (do not take these seriously!):

a) someone or something lifting the boiler off the ground to raise the waterline

b) always operating at a pressure that will push the water up into the returns and therefore seal the horizontal

c) pipe in a fresh water feed into each drop which turns on each time there is steam and therefore fills the drops and horizontal making it "wet" (you will also need to figure out how to get the newly added water out of the boiler)

d) remove the horizontal join and pipe another return line along side the original one and find another tap on the boiler to return it to

e) just cap one of the drops and let the return water back up until it finds another way out

f) leave it alone, perhaps under normal operating pressure, it becomes "wet"

g) overfill the boiler to force the waterline over that join



if it were me, it's look at #2 above -- lower the join if possible and practical to below the waterline.

RAF

Hold on

I thought that there is about a 1/2 LB pressure drop at the end of a Main why would steam want to run up a dry return piped as in the photo?

Also looking at the photo the water line is well above the cross over.

What am I missing here?

RAF

Jamie

As we a talking here I am trying to get in touch with the two pipe system we were talking about the other day to install the false water line on her boiler.

I was at the house the other day and looking at the pipe work in her boiler room

there where two or three dry returns piped together at the ceiling with one vent than the drop into the H/L. Is this working because this is a two pipe sytem with traps?

Jamie Hall

The short answer is...

yes! 



That sort of arrangement wasn't at all uncommon in the early days -- particularly in vapour systems, but also in regular systems.  Many of them used rather ingenious venting schemes which really required that all the venting be done in a central location.  So the traps on the radiators allowed air to escape from them into the dry returns, and the crossover traps at the far ends of the steam mains and dry returns got the air out of the mains, and it all came whistling back to the boiler -- where the vents were.  Then the combined mains dropped to the wet return and there you were.

Jamie Hall

and I might add...

that most of the older coal fired systems seem, by modern standards, to be wildly undervented -- the system for which I am the building super had, for example, only one Hoffman 76 for the whole system (250,000 btu, roughly) (the system now has 4 Gorton #2s on an antler, where the old 76 used to be, and it's only just enough).  But you have to remember that a coal fire builds up slowly -- so you didn't get the rush of steam that we get with a modern gas or oil burner, and you didn't need to let a whole lot of air out all at once.  Much more leisurely.  Rather like life back then, eh?