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# calculating main venting needs

Member Posts: 278
Greetings all.  Should anyone recognize my name from the "Paul System Retrofit" thread, I am postponing that conversion for now.  My current system has zero main vents.  I assume because it was originally a Trane vacuum system.

Anyway, I have two mains.  The last ten feet or so of each is counter-flow (it is all parallel flow prior to the ends).  At the end of each main there is a 90* elbow pointing up horizontally, a short nipple (maybe 8") and then a valve & radiator.

My questions are these:

1) How do I figure out how many vents to use on each main?

2) Having read TLAOSH, I know they need to be at least 15" from the end of each main.  I was wondering though, with the elbows at each end, could I

a) replace the elbows with a "T",

b) send the nipple to each radiator (similar to what is there now)

c) install a short nipple in the new "T",

d) install a second "T" after the short nipple,

e) install an appropriate sized antler-vent on top of the second "T",

f) and then install an additional length of main pipe (15" long or more) with a cap on the end to allow the steam, condensate, etc to pass the antler set-up.  Would this work or will it hammer?

3) Any better suggestions?

Thank you,

Mike

• A Ski Jump Main!

With your description of parallel flow main turning into a counterflow,  I'm mentally picturing something that looks like a ski jump!   Seems to me that the condensate would collect at the low point,  just where does the condensate go?
• Member Posts: 278
Ski jump described : )

The first, I'll say before measuring, 75' of longest main, is parallel flow and pitched down.  Before the pitch changes there are many tee's for branches.  The last "T" is turned down with a short nipple and then a 90* elbow creating a dry return, pitched slightly down for the length of several feet before hitting another 90* elbow (this is my "lowest steam carrying horizontal pipe") and heading down into a wet return.  Coming out of the last "T" (the "T" that drips into the dry return) and pitching upward now, is the last section of main leading to the upward-turned elbow, leading to the last radiator in the line.  This short section (about 10') is counter-flow and drains back into the same condensate return in the last "T" previously mentioned.  The second main, while much shorter, is set-up almost identical to the first main described.  Does this make sense, or at least can you picture it in your minds eye?

Thank you,

Mike
• Ski Jump Mains

Hi Mike-  Thanks for the info. I was figuring on the return being at the low point but have learned always to ask.  What is the size of the pipe on the mains?  Is the main the same pipe size all the way to the end? What is the length of the shorter main?

Are there any other drips on the mains?  I've attached a chart which might be of help in determining the size of  the mains if you need to measure them.

- Rod
• Member Posts: 278
pipe sizes, plus

Hi Rod.  I recently bought an aluminum Pocket Rocket and will soon do a full steam system survey of all pipe, fittings, lengths, pitches, and sizes.  It will be a day or so before I get to this.  As soon as I do, I will answer your questions and will hopefully be able to answer any others.  Thank you for the chart: it is now enlarged, printed and put in my steam binder.

Thank you,

Mike
• Vent Location

Mike - I'm thinking that the parallel main vent might be located after the last radiator lateral before the drip. Since it is a parallel main treat it like a parallel main.  I just wouldn't get it too close to the drop tee as there may be conflict there with the condensate of the parallel and the counter flow mains colliding.

You can tap straight into the top of the pipe. As you're moving about keep an eye out for a good spot with enough clearance between the pipe and the ceiling.  That vent should take care of the parallel main's radiators.

As for the vent on the counterflow main - I'm not sure. Maybe first you could just try it out and see if the radiator's vent can handle venting the counterflow main plus the radiator. If that doesn't seem satisfactory then you can do it like you'd do a counter flow main with a vent on the upper end.

Maybe one of the pros will add his thoughts on this one. Interesting situation having a "Ski Jump" main. I always wonder in a situation like this what the original logic was.

- Rod
• Member Posts: 278
original logic

the best answer I can give, is that it was a Trane vapor/vacuum system.  Perhaps with the vacuum, they were ok with this odd "hybrid"?!?  The vacuum system may also explain the lack of main vents: maybe they were not needed??

Thank  you,

Mike
• Member Posts: 278
system layout

Hi Rod.  Here it is in all its glory.  Ok, maybe not, but it is here as best as I can draw it.  I am not an artist, but tried to accurately represent it.  There is not one single main vent.  I color-coded the pipes and sized them.  Any questions please ask, I will try to answer quickly.

Also, please please keep in mind, that I will convert the system top a Paul-type vacuum system, but likely not until next year.

Thank you,

Mike
• Member Posts: 278
forgoten commentary

Notice there is no Hartford loop and that the boilers riser goes into a "T", creating a "bull head".  Must not have been Masters working on my system.  : )

Mike
• Member Posts: 278
updated info and questions

What I thought was "counter-flow" end-of-mains, are, now that I have done the steam survey, actually branches (I believe that is what they are called, anyway).  All but one branch are counter-flow, in fact.  Also, the mains are not as long as I originally thought (this is one reason for the survey, right, to get everything correct BEFORE modification or repair? :~) ).

The longest main starts out at 2" and runs (left from boiler) about 12' before turning into a 90* and being reduced to a 1 1/2" main.  From that elbow-reducing main, it then travels about 10' , with one more 90* ell about 28" after the main size reduction.  If you look at the drawing, you will see a "T" where a drip is provided.  Very close to the right of the dripped "T", are three more "T"'s for branches.  Moving to the right of dripped "T", there is about 20" of main between second and third "T: and this short piece has a union, making it easier to remove.  Can I put main vents here, in this short piece of main?

The main is also dripped after the ell where the 2" main becomes a 1 1/2" main.  Is this drip a good location for a main vent?

Again looking at the drawing, the short main moving to the right of the unlabeled boiler, the header is 2" and is reduced through the ell to a 1 1/2" main.  This short main is less than 8'.  At the end of this, there is another drip.  Is this location a good one for main vent(s)?

Any and all suggestions/questions/etc much appreciated.

Thank you,

Mike
This discussion has been closed.