Phantom Air

bob_60

I have been having a problem with my hot water old Cast Iron radiator system.  I installed a modulating boiler 2 years ago and at the beginning of this heating year I flushed and drained the system and added antifreeze and boiler descale and water treatment and refilled the system.  Had a very successful heating season but about 10 days ago, I would begin to get large amounts of gurgling when the system was off during the night.  I found that the radiators on the lower level were full of air and purged.  Now I have to do this regularly and as water cools the gurgling continues regularly.  I have a large air separator on the supply make up above the expansion tank.  there is a large older expansion tank, I assume, attached to the supply side of the heaters.  I found one side which says drain is attached to both supply lines and the other end of the tank has a pipe plug in the same position as outlet attachment.  there is water coming from both locations when the plug and connections are loosened.  The tank is an old Thrush unit suspended in between the floor Joice.  How did these old expansion tanks or surge tanks work?  is it possible the bladder has ruptured and I am drawing this large volume of air into the system.  I have checked for leaks and could find none in the system,  Could the antifreeze/boiler treatment have caused the tank problems?  should I be looking elsewhere? This started life as a gravity system and the old expansion tank is still hanging upstairs but disconnected. thanks, Bob

Mark Eatherton

A picture....

is worth more than a thousand words around here.



Got a digital camera?



As Johnny Carson was wont to say playing the role of Carnack the Great, "I'm trying to read your mind, but I keep coming up with blanks!"



ME

Big Ed_4

B&G Airtrol Fitting

Air can migrate out of the old steel tank though a current in its supply pipe ... You can either install a B&G Airtol fitting in the tanks supply port to prevent the migration or change the tank to a diaphragm style tank ...

Gordy

Fresh batch of O2

  I'm not a pro, and I may be making some assumptions but......

  I think when you flushed your system you started the whole air removal process over again. O2 comes out of solution the hotter the water becomes. If everything was fine after commissioning 2 years ago, then it could be possible you did not get the system fully purged when you did your flushing. Now your bleeding radiators, and adding make up water. Thus adding more fresh oxygen enriched water.



    If you have the old steel expansion tank Big Ed is right about installing a bell and gossett airtrol tank fitting. What happens is ghost flow from the cool tank water to the system with in the same pipe. The water in the tank is exposed to air which is the cushion in the tank, the water absorbs oxygen from the air cushion when the water cools, and migrates back into the system then it heats up releasing the absorbed o2 in the system. The airtrol tank fitting stops this migration.



    An air seperator only works if the system water is flowing through it. In the last 10 days it seems your system is not running as much because of warmer weather. The radiators are acting as your air seperator because water comes out of solution at lower velocity rates which happens to be the radiators in your system.

 Air comes out of solution at lower velocity rates, and higher temperatures.

 Air stays in solution at higher velocity rates, and cooler temperatures.



Think like air, and water, and you can solve a lot of problems.



Like ME said though a Pic is worth a thousand words of the near boiler piping.





Gordy

bob_60

pictures of plumbing/boiler

I have attached some pics.  evolution of heat.  Coal, oil, package, condensing, modulating.  all in one place!  For now!

Small 1/2" line goes off supply lines to horizontal tank in ceiling, pics 4-5.  I have ordered a larger diaphragm tank and thought I would disconnect the old tank.  There is about 350 gal in system  Bob

Techman

Air

o.k. ill bite! is it O.K. to have two different types of  expansion devices in one water system?

JStar

Whew...someone else asked first.

I would say, just cut out the old steel tank and leave the diaphragm tank in place (properly sized). I can't imagine why you would keep them both. And it would seem that the old steel tank is no longer used for compression, but as an air storage tank.

bob_60

large tank

How did these old surge or expansion tanks work?  Was there any seperation between air and water, ie bladder design?

JStar

Tanks.

No separation at all. They are true "compression" tanks, because the water pressure compresses the air inside the tank.





http://www.bellgossett.com/homeowners/CompressionTank.htm

Mark Eatherton

Wow.....

3 boilers eh :-) Matches my all time record high.



BTW, you have some open exposed asbestos on the old boilers flange that needs immediate attention. Paint it with latex paint, then protect it.



Better yet, get a pro in there to fully abate it, then you can either move it into a corner of the basement, and hook it up to your heating system with a non electric TRV and have the worlds largest cast iron radiator.



Get rid of the ceiling hung expansion tank. It is most probably water logged, and will continue to get water logged due to the air eliminators on your system. Make certain that ALL pumps are pumping away from the diaphragmatic expansion tanks connection to the system.



You probably already knew this, but it is worth repeating. These older standing cast iron systems are a "bottom fill, top vent" system. In other words, you can't power purge them.



Also important is the condition of your existing newer expansion tank. They too can become water logged and give some of the problems you are experiencing. With ZERO pressure on the water side, check the AIR pressure on the air side. It should equal the minimum fill pressure needed for your home (.5 psi per vertical foot plus 5 PSI to avoid flashing to steam and leaving residual pressure at the top to push air out of the radiators.)



Silly question, but why anti freeze?



ME

bob_60

antifreeze

we live in southern Nebraska and after last years ice storm we were w/o power for almost 2 weeks in areas.  The antifreeze was a thought at a preventative measure in case it happens again.  The next stage is the installation of an alternative source of heating. 

the asbestos problem needs to be handled on all the piping.  They were proud of it back then and marked it all with stickers, asbestos insulation.  I worked in power plants for years and have had to deal with it for a long time.  This summer should be taken care of.

I have ordered a new expansion tank, a Sparco-trol tk300-90 and will check the other tank charge.  I will disconnect the compression tank.  After reading the B&g article, I think this is where the problem lies.  I will take out of line today.  thanks for all your help.  It has been years since I have dealt with these systems.  I still remember throwing coal at 2AM when it got frigid back in Jersey as a kid.  That old steam system sure kept our old house toasty.  Thanks for all your help.  Quite an education.  I will let know how it works out.  Bob

bob_60

success

Disconnected the compression tank as suggested.  No more gurgling or air entrained!  Just good , quiet heat.  I will upgrade to larger diaphragm when it arrives.  Spring is here this week, won't work heat hard.  time to AC!  Thanks for all the help!!!   Bob

Techman

Ta DA

finally got one right! BaDa Bing,BaDA Bang,  BaDaFuco.Thanks Dan H. for your books!

JStar

Happy Endings.

Can't wait for next winter!