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Slow condensate return

Landy
Landy Member Posts: 7
Thanks for the help in an earlier thread (March 28,2013) "Working out issues with Dunkirk PSB-7D replacing old boiler", where I discovered that I needed vents at the end of the steam mains to get steam out to the ends quickly. We have done that and reduced the time it takes to get steam to the end of the mains down to 2 minutes from the earlier 16 minutes from the time the boiler stars producing steam pressure. The house now heats quickly and evenly, but I have another problem. After running a few cycles, the boiler over fills with water and stabilizes at about 3/4" from the top of the site glass, which is less than 2" from the bottom of the steam take-off to the header. I am concerned that this is producing wet steam, especially early in the cycle.



I have observed 2 thinks that worry me. First, the LWCO is a probe type HydroLevel CycleGuard CG400-2090 and with the boiler off, it indicates low water condition at the proper level, yellow light on when below the probe and off when above the probe. When the boiler is steaming and the water level drops as the steam leaves the boiler, the sight glass shows the water level dropping about 4" below the probe before the CycleGuard indicates low water (this is about 2" from the bottom of the sight glass). When it hits the 20 minute cycle of turning off the boiler for 90 seconds to let any foaming go away, it suddenly realizes the water is low and calls for more from the Honeywell automatic feed, which dumps a gallon of water in. That still isn't enough, so the CycleGuard calls for more and gets either 1 or 2 more gallons before the water level rises above the probe on the CycleGuard. If I shut off the boiler and wait for the condensate to return to the boiler, this extra 3 gallons matches the "flooded" water level I see after the boiler has run a few cycles. Is 4" of foam/splatter in the boiler to keep the probe conducting normal?



Second, if I turn off the boiler when it has gotten to the low point 4" below the low water cutoff and wait for the condensate to return, it takes about 20 minutes for the water level in the boiler to rise that 4" to get above the low water level and satisfy the CycleGuard to allow the boiler to start operating again. 20 minutes for the condensate to return seems long to me. We have about 42" of A dimension and the wet return piping was completely replaced when the new boiler was installed in December 2012. What else would cause slow condensate return? Does 20 minutes sound normal?



A few system facts: There is a video tour of the boiler system that I posted on YouTube at <a href="http://youtu.be/wNlzfB3zS_A">http://youtu.be/wNlzfB3zS_A</a>, if you want to see what the piping looks like. There are two steam main runs, each about 70' of 2.5" pipe, ending and dropping down to the 1.5" wet return. There is 726 sq ft EDR, if all radiators were open fully, which they are not, which translates into about 175,000 BTUH. The Dunkirk PSB-7D is rated at 220,000 BTUH and seems to have about a 7 gallon capacity when filled to the Normal Water Line. That 175,000 BTUH translates to about 0.4 gallons per minute and I see a little less than that once the condensate does start to return after about 20 minutes of steaming. We are running the boiler at 12 oz/sq in max with 6oz/sq in differential, although I almost never see the pressure build above 6 - 7 oz /sq in while running. The system seems to take all the steam the boiler can generate and doesn't let the pressure build up to where the VaporStat ever cuts off the boiler on high pressure.
Homeowner with new (12/2012) Dunkirk PSB-7D steam system with 726 sq.ft. EDR in a home built in 1925.

Comments

  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,424
    Slow condensate

    Is the waterline steady?

    Has it been thoroughly skimmed, and then refilled with pure water. There should not be any foaming.

    Is the probe in the right hole?

    Is that header sized right according to the installation instructions? It looks small. I don't think that amount of water could be evaporated away in that period of time. It may be blowing up into the steam main, even at low pressure. Valve off the auto/ over feed, and see whether that improves things.

    Could there be a horizontal part of the return at about waterline height, or just above which is hiding the water?--NBC
  • Jamie Hall
    Jamie Hall Member Posts: 15,355
    It strikes me

    that somewhere out there you have a fair amount of condensate hiding.  The water level from the feeder is probably a bit high, and you may be getting some carry over -- but that should come right back through the equalizer.  20 minutes for the condensate to come back up seems long to me.



    So... I would take a look at any and all wet returns, to see if there might be one which is partly clogged.  Or really clogged.  I also like NBC's idea of a return at just the right height to store some water, although I'd expect that to come right back when the system shut down...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.
    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • Bio
    Bio Member Posts: 278
    Water

    Something similar happen to me with my new boiler, for a moment I thought it was undersize or it had a small water capacity, I had skimmed numerous times and I never thought that was the problem, until mid winter I flushed it completely for two weeks in a row and the water level stayed about 3/4" below the NWL in the coldest days



    I suggest keep skimming and flushing, there is a lot of oil in the boiler and piping, also if your venting the radiators too fast, that can also cause delays for condensate to return, good luck
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