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Arco vapor system

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gerry gill
gerry gill Member Posts: 3,078
quality main vent in its place..vacuum isn't needed unless your still on coal in your area..you may be experiancing heated air rising out of the boiler by convection, (just like gravity hot water)..

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Serving Cleveland's eastern suburbs from Cleveland Heights down to Cuyahoga Falls.

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  • kev
    kev Member Posts: 100
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    arco vapor system

    I replaced a boiler connected to a arco vapor system and also piped an indirect to it. After much searching I found the No. 916 ARCO air eliminator in the ceiling at the end of the dry returns. One side is plugged and the other has what looks like an original vacuum vent. Can I replace this with a standard main vent or do I need a vacuum style. I fired the unit today to get hot water and noticed the boiler was building a slight amount of pressure and the header and mains were beginning to heat. I only had the aquastat set at 140 Degrees. Should the pressure be released through the rads and down through the arco eliminator as it is being used for hot water?

    thanks for any input.
  • kev
    kev Member Posts: 100
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    why the pressure

    in the boiler as I lift the relief valve? Also there are no vents at the ends of steam mains, the system is just like the one shown on page 269 of THE LOST ART. Should I add vents to the mains also? Of course the system worked fine before I converted the boiler from oil to gas. Thanks.
  • Christian Egli_2
    Christian Egli_2 Member Posts: 812
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    CPR diagnostic

    Is the slight pressure you observe the one puff from the boiler as you open the relief valve? It's not a sustained steaming pressure, is it? I am also assuming you have thermostatic traps at the radiators.

    Two pipe vapor systems run with near zero pressure, steam has to move very easily and very quickly to the trapped radiators. Traps on all radiators provide huge venting opportunities for the system, thus, on these two pipe systems main venting is a non-issue (radiator traps are) and end of main venting is optional (it's really only to remove the last appendix of air beyond the last venting radiator, without the appendix - no need for cross over trap vent or their lesser substitute on two pipe, the one pipe main vent)

    Tow pipe venting issues are all concentrated in the return lines. These carry back condensate and vented air from the upstairs radiators. Condensate easily piles back into the boiler if you're not operating the boiler at any more pressure than the B dimension commands (on the order of 1/2 PSI).

    Air expelled beyond the venting at the thermostatic trap also needs to be funneled away, it's been trapped once, it doesn't need to be trapped again. Thus, it finds its way out through the air eliminator - which is not and should not be a steam stopping device.

    Often, the little vacuum protected hole gets rusted shut. Often also, puddles and sags in the return lines obstruct the air passage. Neither of these conditions are good, they're terrible in fact: without proper air expulsion at the air eliminator hole on two pipe systems, you're not going to get proper steam travel.

    Your puff worries me a bit. Try this first.

    Do some mouth to mouth resuscitation to your artificially kept open safety valve. Your breath will simulate steam, and like in normal steam operation system air will have to be expelled out the other end. Take a deep breath and blow in. Then, as you move your lips away get a feel for what is or is not coming back at you through the open relief valve.

    If nothing blows back, try again with a deeper breath. Getting no blow back is the ideal situation that indicates proper air venting. An assistant caring over the exhaust hole at the air eliminator location should detect the blow of your breath as you insufflate the boiler: no delay venting at the air hole is ideal.

    Next

    Getting slight blow back shows some decreased capacity, mostly this would be from a partially shut air hole or plainly an air hole size too small on top of the air eliminator. Remove the faulty hole, vacuum options were only useful on old coal operation and not worth their built-in constriction today. Simply remove the vacuum module and plan to replace it with a nipple unthreaded on one end. Test again. Now there should be no blow back.

    If there still is, perhaps the air eliminator float is jammed. Open up the other plugs and see what comes out in form of air. Water logged sagging returns would be the next big source of problem. All shut radiator traps could be a last problem. The air eliminator is only useful on out of control raging coal fires. Controlled gas fires never get there and so, replacing the entire eliminator with a bit of open spill pipe like we would a relief valve is the next thing to do.

    ***

    I say all this, because your system is giving you a bit of puff which you should not be getting at all. Thus, I suspect a bit of faulty air exhausting. Taking away the vacuum obstruction should work wonders next winter - faster heat all the way up to the last radiator and even more silent steam operation. Silent and quiet aren't even the proper words, it soundless.

    But you're getting a bit of puff right now in summer operation... where could that come from? Well if it's only a small puff, we could explain it through simple water expansion on 140F heat rise - we know how we need expansion tanks on closed hot water heaters, they're about the size of what a human breath is, so our earlier mouth to mouth test is realistic. Air above the water in the boiler also gets very hot, and so it expands to also give you a bit of puff. The small puff is all explained by a faulty (meaning plugged) air hole.

    If it's a big puff, you could be looking at a treasonous aquastat heating the boiler closer to steam temperature than we think. It is normal to see the near boiler piping heat up a bit on hot water production. A lot? no.

    ***

    For summer operation it might also be a good idea to flood the boiler and move the water surface (where most corrosion occurs) up into the take off - you'll have less evaporative surface and less air contact. This would also transmit less heat up into the header. This method is often provided as a method for lessened corrosion during the summer break.

    In the fall, make sure to lower the level again.

    ***

    Obviously, playing with water level is an invitation to flooding the whole system. To make all this totally foolproof, rather than the air eliminator, I prefer the spill over air hole. The open air hole discussed above can just as easily pour out any excess water from a faulty fill valve. Pipe the cut nipple like we would pipe an ordinary relief valve, that is down to the floor near a water drain, and you'll never have anything to worry about the system. All faults will be easily visible from the safety of the boiler area.

    ***

    Make sure also your pressurestat is set low. B dimensions dictate maximum allowable which are very rarely above 1 - 2 PSI.

    Now go give your boiler the kiss of life.
  • kev
    kev Member Posts: 100
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    No traps

    are on the rads. Its an ARCO system, just as pictured on page 269 in LOST ART.
  • gerry gill
    gerry gill Member Posts: 3,078
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    Try taking off the vacuum vent,

    and with just an open hole venting to the atmosphere, then does all work well? if so put a gorton#2 up there.

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  • Christian Egli_2
    Christian Egli_2 Member Posts: 812
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    The master vent on the pressurized returns

    My apologies for taking your ARCO mention only as a generalized description. Well, now we know exactly what's at the radiators. Your page 269 is an orificed steam distribution system with (instead of steam stopping traps at every radiator) a system of pressurized returns exactly like in a one pipe system.

    Your 916 is the one pipe transplant where all the radiator venting is replaced by master venting. The larger 915 version which is pictured on page 269 is a cross with the two pipe radiator thermostatic trap systems, except that ARCO replaces the radiator traps with one master trap. In both 916 and 915, the returns can become pressurized with steam.

    And my apologies for making this more complicated than a two word response.

    Your 916 calls exactly for what a main vent is. You have two slots to install them, I would install at least two new main vents. Possibly more. We load smallish one pipe systems with several main vents and all the radiator vents - it's a bit much to expect your system to do all that and more venting through just one or two Gorton style main vents. You'll need to check the most excellent Venting Charts by Gerry above.

    Note also that in your special system if your boiler is adequately undersized, there will never be a need for those master vents to shut.

    The blow test described above still applies and your air flow should not puff back at you. You should observe the same response without master vents installed as with the master vents in - this way you'll know how close you are to having enough venting capacity. Gas boilers need more venting capacity than was originally planned on coal fire.

    About installing one pipe vents everywhere

    The orificed system relies on a steady pressure gradient sloping downwards from the boiler to the air exit hole. The slope has to be steady, and if there are any bumps in the way, the orifices won't work they way they were intended by the original installer. That's why these systems have only one hole for predictable gradient. Insert main venting elsewhere and you don't necessarily know what's going on anymore. (Not that you can't install extra main vents, but that you should first be very sure about what problem you are curing)

    The proper pressure gradient within the pipes is equally important on steam fill up as it is on steam retreat. Again, here the order we have with one exit only is in jeopardy of being disturbed by extra exits here and there.

    Fix the puff back pressure first, get proper master vent function, then worry about possible main venting problems and possible pressurized return venting problems.

    Then, it should all be a thing of beauty. Thanks for the details. All that and for the answers that go straight to the point, stick to Gerry's posts. Best regards to all.
  • kev
    kev Member Posts: 100
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    Thanks

    for the response gentlemen, I will be going back on WED. to skim boiler and change the single vacuum vent to two standard main vents. Unfortunately there is not enough head room for GORTONS. 5 1/2" to be exact. Thanks again!
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