cycling on low water/slow condensate return - overfired?

BigRedSteam

Hi folks...could really use the help of the great steam minds on this forum.

Now going on season 3 with adopted 1-pipe steam system in new (old house). Lots of tinkering, cleaning, etc to get things quiet with a stable water line and working well. Recently made some changes that have improved things but uncovered a new issue...Cycling on Low Water. Looking for advice on how to fix/tame this without getting into pumping condensate..

Details on the system in my 3 floor 4000sq ft 1909 victorian
Boiler: Dunkirk PSB7D 181k/137k btu (gross/net) (571 EDR rating)
Connected Radiation: 145k/115k (gross net) or 460EDR
Boiler skimmed a few times and water is clean and level pretty steady(though not as steady as I would like).
Return lines flushed recently - clean
Near boiler piping very good.....I get dry steam.

TWO BIG CHANGES RECENTLY may have contributed to low water situation:

1-added radiation on 3rd floor - 3 small rooms for a total of 10k btu added. Vented top of 3rd floor risers
2 - Recently removed cyclegard and replaced with safeguard - HUGE difference in comfort and length of cycle. Used to cycle on 15-20 min intervals..now get runs of 30-45 mins...on avg

LOW Water scenario
I sometimes see cycling on LOW water on runs lasting more than 35 mins. Cyclegard used to shut the boiler down before a low water condition was realized. Occasionally now the water level is below the probe BUT way above the manufactuers MIN LOW water line....(That probe is super highon the boilder..dumb??!) It seems a bit better when the 3rd floor rads are valved off. I placed water feeder on a 2 min Dwell and that is enough time to let condensate return w/o feeding water.

Based on boiler rating vs. connected radiation I'm clearly overfired and my guess/hope is that by turning down the fire a bit i can tame the situation. Any other ideas?

Jamie Hall

For starters, is that the longest dwell available on your water feeder? If not, try setting it on a longer dwell. The place I care for uses a 10 minute dwell on feed.

Then the next thought is -- when those third floor radiators were put it, are the pipes really big enough for the EDR? Pitched adequately? That could give you a slow return from that area.

BigRedSteam

Hi Jamie..

Feeder:
it is the longest dwell..mcdonell miller wfm-24 using setting #4(120sec)...setting #2 is recommended BUT has a 60 sec dwell and flooded boiler.

with as much as a whole section more than I need on my boiler I am hoping/expecting to NEVER go off on low water..If not for this issue I could have really nice 30-40 min runs to satisfy all rads and thermos

Piping: The largest of the 3 RADS(4.5kbtu) is on a 1.25" riser that is dripped. The other two rads are smaller, less than 3k btu each so not too worried about those guys. Pitched correctly..yep

BigRedSteam

bit of an update...I tested pressure on the valve. Manometer indicated 3.95WC. Dunkirk specifies 3.5. Installer (before my ownership) must have played with this to get heat to cold rooms(the pressuretrol was also on 5 or 6psi). It was way overfired. I turned it down to 3.3WC (a modest 5% underfiring). I will observe if that helps. Per valve operating specs cannot go below 3.0WC.

Fred

I assume you turned that Pressuretrol down so that Cut-in is .5 PSI and Cut-out is 1.5 PSI? Pressures of 5 or 6 PSI can certainly make it difficult for condensate to return to the boiler.

BigRedSteam

Fred yes first thing I did when taking ownership ofthe house in 2014. Shortly thereafter repiped boiler and improved venting. When I repiped my installer did not touch gas pressure however and that was changed today

Fred

Are you sure there isn't a tapping on the boiler that may be a little lower, for the probe? This is a case where a float type LWCO (like the McDonnell Miller #67) that mounts on a Tee on the bottom port for the sight glass makes sense. I have one on my boiler. It requires a weekly blow-down, during the heating season but it sounds like it puts the Low water level down lower than your current tapping???

BigRedSteam

not sure...but I will check it out or call the manufacturer...The probe location is ridiculously high on this unit so anything to move it down is a good thing. If not I will look to switch out in warm spell or next season. I am still hopeful that downfiring will help...less condensate running around in system piping = more in boiler. downfiring will hopefully makes things more orderly if not a bit slower which would permit condensate more time to return..but that is my uneducated guess

BigRedSteam

Hatterasguy..i'm intrigued. Can you post a pic or two... I imagine you piped a 1/2 in T off the bottom of the gauge glass and into a reducing T perhaps a reducing one to accept the 1/2 and allow the probe to sit in run in a larger volume of water

JUGHNE

I was adding a required redundant LWCO (1" MPT) to a boiler which presented only a 1/2" port.
I used a 1 X 1/2 X1/2 Tee screwed into a short nipple in the block.
The probe went into the 1" port and then a blow down valve added to the take off of the tee.
Blowing this valve down will not activate the LWCO, but assures that the reducing passage way is not plugged and allows some cleaning of the probe. FWIW

BigRedSteam

thanks hatterasguy..so In taking a look at my boiler this will be tough for me to do this season. The pigtail for the ptrol is located right next to a riser outlet Tee and there seems to be no way to remove this unless I remove the ptrol and cut the pigtail. It also looks like hydrolevel has a unit called the 711 which is a sightglass mounted probe system..connects to the safgard400. Uses two probes one(lower) to sense low water and cut off the firing and the other(higher) to sense water level. something to consider as well.

BigRedSteam

thanks hatteras...makes sense now and I can totally fit this on the boiler. In the next few weeks will give this a try. I think I will leave the existing probe in the block and buy a new for this setup. would be interesting to create a setup where the lower probe shuts off the burner and the higher probe serves as the shutoff for the water feeder...much like the arrangement in the 711 from hydrolevel...