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Help identifying skimming tap

Hello all, newbie to the forum here... Trying to figure out how to skim this old Slant Fin Liberty boiler. I think I have enough to go on as to how skimming is done, but my question is about identifying the location of the skim tap. I believe it to be the tap behind the low water cut off, which currently in this picture has a pipe going downward and valve attached to it. ( not of my doing ) Is that correct?

If so, my next issue is, I have filled the boiler to above this tap and opened this valve just to see if it drains , but nothing at all comes out. I assume it’s maybe plugged with sediment for lack of any flushing... but I don’t know that yet. I guess my next step might be to remove this pipe and valve and see what’s up.

Can you guys point me in the right direction on skimming this?


  • neilcneilc Posts: 661Member
    open that ball valve all the way,
    now poke up there with your longest screwdriver,
    if this doesn't break the slug at the valve then you get to disassemble.
    It might be blocked at the boiler port also.
    turn the boiler off, drain below the level, and disassemble,
    Let us know how that makes out.
    Oh, yeah, that's what you have for a skim.
  • FredFred Posts: 7,853Member
    That is the skim port. You should not have to drain any water out of the boiler, if you need to take it apart to clean the pipe and the tapping into the boiler. That tapping should be above the boiler water level. You can look at the water in your sight glass to verify that.
    Also, do you ever open the valve on your LWCO (the McDonnell Miller #67) and blow it down weekly like you should? You need to keep the crud blown out of that unit for it to function properly. That should be done once a week during the heating season.
    Once you skim and blow down the MM 67, you should open the drain valve somewhere on the bottom of the boiler and drain water out until it runs clear. Do that about once a month during the heating season. If it hasn't been done in a while, that drain may be clogged as well.
  • DIY_GuyDIY_Guy Posts: 38Member
    Thanks for that info guys. I do a weekly blow down and the water levels aren’t doing anything crazy but I thought I might do a cleaning next week and skim it as well. I’ll get back to you on how it goes. I have recently opened the boiler drain, and the wet return drain as well, and they were surprisingly clean.

    I’m a couple seasons now into learning about steam heat and trying to get this running as efficiently as possible. It’s a heat system that intrigues me and I’m really enjoying learning about it. I insulated most of the mains last year at the suggestion of an energy auditor and I also added main vents last year-of which it had none, so now it’s become a quest! This is a large, older, mostly uninsulated building and this is a second floor apt. The heat seems to move ok, is relatively balanced, no water hammering, although tenants complain ocassionally of whistling radiator vents and during that cold week around thanksgiving it used a LOT of fuel.

    If I can continue with some other things I’m wondering about: the boiler seems to be quite oversized and seems to be short cycling ( off/on) a lot while getting the apt up to temp. The boiler is rated for 421 sq ft of steam and if my calculations are even close ( this part is very new to me..) the 5 radiators it runs are around 185 EDR [x 1.25= 231.25sq ft) I have a feeling this 1993 boiler ( or maybe the one it replaced) previously heated other floors in the building, which are now on forced hot water /natural gas.

    Last week in a quest for efficiency, I swapped out the pressurertol and put on a vapor stat with a 0-5, psi gauge. It still cycles often while heating up, but is keeping a much lower pressure overall. The apt is empty just now so I’ve only been running it once a day for an hour to keep things from freezing, so I haven’t yet seen how differently it will perform with the vaporstat when maintaining a warm apt. I’ll do this soon.

    I guess what surprises me is how much it turns on and off after it starts making the steam. Is that anything to worry about or try to remedy?


  • ethicalpaulethicalpaul Posts: 694Member
    It sounds hugely oversized. Insulating the mains, while great, has increased the oversizing. Only 5 rads? I have 8 for 200 EDR but 4 are quite small, maybe yours are all large.

    You are coming back from a large setback so that’s going to make it repeatedly cycle on pressure since it’s making so much more steam than the radiators can condense. Better than burning fuel for no gain though. Others would crank up the P-trol to reduce the cycling but you know better.

    What’s the 1.25 multiplier you are using in your EDR calculation?

    The vents should be whistling a lot less if your main venting is good and your pressure is lower, but since they are on the second floor, the air in the risers still has to go through the radiator vents each cycle so that can still be a lot of air—again, each cycle.
    1 pipe Utica 112 in Cedar Grove, NJ, 1913 coal > oil > NG
  • DIY_GuyDIY_Guy Posts: 38Member
    re: mains insulation- yeah, I thought that might be a factor.

    I noticed the higher pressure was also pushing some water out through my water supply valve/knob every time the furnace shut off and I was losing some water there. No more issue with that at the lower pressure.

    it's the first time I've attempted to calculate EDR, but seem to have picked up somewhere in reading to use that factor for calculating boiler size from the EDR... not correct? Either way, it seems rather oversized. I suspect whoever replaced it just went with whatever the old one was or maybe even went larger.

    the radiators are 36" tall column type. 4 are roughly 18-24 inches long and one is maybe 12". The kitchen and bathroom have no radiators at all, and I actually wondered about adding one or more to help with oversize issues, if I can figure out how to pipe them. I have an extra radiator (unused) in the basement.

    Even though I've swapped them out, the vents on the largest radiators seem like they don't really fully close, or maybe do only for a short periods and then start to puff a bit more air out, even though the radiator is good and hot. Is that normal operation? I also took one off today and it had some water in it. Normal?
  • ethicalpaulethicalpaul Posts: 694Member
    The EDR you calculate from your radiators should be matched against the _net_ sq ft from the rating plate. That net value will already have calculated that extra factor.

    The EDR should come from the height, the number of columns in each section, and the number of sections in each radiator but you may know that already and just told me the general size to answer my question.

    I like your idea that other floor(s) used to be served by this boiler. Can you find abandoned pipes?

    I think some water in a vent is reasonable but it may be due to wet steam. I had a type of vent that would click when it opened or closed and I could hear it opening and closing several times in a heat cycle. So if you’re watching really close you might see that. As the steam condenses and the end of the radiator cools a bit the vent can reopen briefly is my thinking.

    We’d all love to see your boiler with its near piping from a few feet away and a photo of its rating plate, plus your nice new main venting!

    Also I misspoke earlier. Your system shouldn’t have to push out all the air every cycle for those cycles that are due to pressure during a single heat call because the fire should return while there is still some pressure in the mains. Sorry about that.

    Finally, how do you know the level was above your skim port? Not accusing, just asking 😃. On mine it seemed like I had to fill way above the sight glass before it started running, but I have a Utica and the push nipples between sections may be really high.
    1 pipe Utica 112 in Cedar Grove, NJ, 1913 coal > oil > NG
  • DIY_GuyDIY_Guy Posts: 38Member
    Good idea to look for old pipes. Is horizontal piping from one room/radiator to the next an option, if it is pitched enough to drain back to the first radiator?

    As to the skim line, I ran the level up past the top of the sight glass but wasn’t sure if I should go further but I’ll scope that out on my next visit. The top of the sight glass seems above the tap. You can kind of see the pipe to it in the picture, above and to the left of the LWCO

    I’m fairly sure the near boiler piping is not up to snuff. The header is about 18 inches from the waterline and it also reduces immediately from 3” to 2” at the first turn into the header, before it gets to the two risers. I gotta think it’s pushing wet steam, but with no hammering, I guess I have to think about how much gain I’d get by changing it, but it is on my todo list to examine that. I’ll get some pictures for you.

    Thanks for the responses, great forum!
  • ethicalpaulethicalpaul Posts: 694Member
    edited December 2018
    The pros might say something, but I would try to avoid chaining a radiator off an existing one.

    Ahh I see where your sight tapping is above your skim port, makes sense that it’s blocked.

    I agree, if it’s working OK I wouldn’t mess with the NBP in the winter. Although I did mess with mine LOL.
    1 pipe Utica 112 in Cedar Grove, NJ, 1913 coal > oil > NG
  • FredFred Posts: 7,853Member
    The more I look at your boiler, the more I'm not sure what they plumbed to be a skim port is actually a skim port??? The skim port is suppose to be above the boiler water line. The Low Water level for the MM#67 low water cut-off is the very topline engraved in the casting of that LWCO, which means the normal water level should typically be somewhere above that line and that would seem to put your skim port under water. I'm guessing they used the wrong tapping for the skim port.
  • ethicalpaulethicalpaul Posts: 694Member
    Yeah I agree, and I’m using that as a defense for why I assumed it would be above the sight glass! 😅
    1 pipe Utica 112 in Cedar Grove, NJ, 1913 coal > oil > NG
  • DIY_GuyDIY_Guy Posts: 38Member
    Here’s a frontal picture I had on my phone. That port is about equal with the waterline. I don’t see any other taps higher, which is why I wondered about it.
  • DIY_GuyDIY_Guy Posts: 38Member
    I found a manual for a Slant Fin liberty ll series boiler online ( newer version of this one) It’s similar and they do call that port the skimming port.

    Though they post some, I’m not sure why Slant Fin doesn’t keep full vintage manuals available. In fact, it looks like they’ve redacted some of the info about mine from the L series manual. Guess I’ll have to ask them.
  • FredFred Posts: 7,853Member
    As long as it is above the boiler normal water line (and it looks like it is) , it will work as a skim port.
  • DIY_GuyDIY_Guy Posts: 38Member
    Ran a screwdriver through the open valve. Still plugged. Looks like I’ll need to disassemble it.

    Here are some pics of this boiler. It looks rather disheveled but runs ok and I’ll straighten it up when I clean it next week. It’s a single pipe. dry return set up.

    In these pics, You’ll see the main vents. I tried different types on the two runs. The big gorton is a couple minutes quicker to get heat to it but it also has 1 less riser on that leg. I put the main vent at the end of the runs before the last risers that go up to the second floor. Both runs have dry returns and I’ve since realized I probably should have put the vents at the ends of the dry runs instead. Will moving them make much of a difference? The dry returns are maybe 20’ of 1” pipe. I also have not insulated the dry returns, yet. Should I?

    One pic shows the dry run and you can also see where they return near the top left of the boiler picture.
  • FredFred Posts: 7,853Member
    Don't move those vents. They are fine at the end of the main, just past the last radiator run-out. There is no need to vent the returns. Also, how long is each main? I wonder if you have enough venting on them. The Gorton #2 is typically good for about 20ft. of 2" main and those two bullet style vents on the other main are very likely too small for almost any main.
  • DIY_GuyDIY_Guy Posts: 38Member
    Fred, I think you’re probably right about needing more venting, the Gorton is at about 25 feet from the boiler. The smaller 2 are about 42 feet. I’ve got a Big Mouth coming tomorrow which I thought I’d try on that longer line. And then maybe I’ll move one of these smaller ones over with the Gorton.

    What about insulating the dry returns? The do get pretty hot, though I’m sure the first floor benefits from the heat being released under their floors. (as well as the risers passing through their rooms!)

    To be clear, if the pictures aren’t... these main vents are near but not quite in what I think of as the dry returns. The Gorton is near the end of a main run that runs down the building makes a 90 horizontal turn to an exterior wall (about 5 feet) hits the Gorton and then rises vertical to the second floor. Back near the 90 turn is also a separate dropped pipe 1” that feeds the condensate back to the boiler. This is what I thought to be called the dry returns... maybe incorrectly? So to my novice eye the Gorton is in the main path, not the dry return. The two smaller ones are similar and are tapped off the main pipe in a horizontal short pipe before it goes vertical. Still ok to leave vents as is?

    I disassembled the skimmer tap today. Fortunately it was just the down pipe and the 90 elbow that were plugged. I hit the elbow with a MAP torch and the connections loosened up easily with a pipe wrench and cleaned up ok.
  • DIY_GuyDIY_Guy Posts: 38Member
    One last thing about the pictures. You’ll see one of the vapor stat and gauge. This was the high when it kicked off. The vaporstat manual says it controls a system “up to 4 PSI” , but if I set if all the way up, for 16 OZ, it shuts off, correctly, at just over 1 PSI according to my gauge. The part I don’t understand is how anything above 1 PSI could come into play with this control. What am I not understanding here about how this operates?

    Also is there an optimum range for the high and differential settings? Is there any reason not to set the differential to go clear back to zero before refiring?

    Thanks for your time!
  • FredFred Posts: 7,853Member
    @DIY_Guy , that Vaporstat is a 0 to 16 ounce model. It is set to ut out at 12 ounces and Cut-in at 2 ounces (Main minus Differential) . It is set fine. Based on your gauge, it (or the gauge) may be off by about 4 ounces but still well within a reasonable range.
    As for the Main Vents. They are fine where they are. They vent all the air up to those risers. Moving them to past the riser will only vent a very small amount of additional air. If you have a problem with getting steam to the second floor, and you can't resolve it with the radiator vents, you may want to consider a vent on those risers, just before the radiator , still leaving the radiator vent on the radiator. Not usually necessary though.

    The greatest benefit of insulation is on the steam mains. Some do insulate the returns but it is not critical, especially if your are getting some benefit from that heat.
  • DIY_GuyDIY_Guy Posts: 38Member
  • DIY_GuyDIY_Guy Posts: 38Member
    Hope it’s ok to keep going in this same thread though topics have expanded... my pics are here so maybe are easier to reference.

    The big mouth came today, So for comparison I did a cold start of the furnace with one of those smaller main vents completely removed. That gained me about 2+ 1/2 minutes in speed of steam in the main to that point from my last measurement with the two vents installed. I shut it off at that point and installed the big mouth in the vacated tap. I will measure that time at next opportunity,

    I switched out one of the radiator vents and much to my surprise, all the radiators got fully hot and the vents on them closed within 2 minutes of each other! Though I went downstairs and the furnace was still running and pressure was starting to build but it was only at about 6oz at that point.

    So my question is: Is there any reason for me to run the pressure on that system any higher than 6 oz if that completely fills the radiators? Doesn’t it just build extra unneeded pressure at that point?

    If it makes any difference to the equation. it was it was 40 out here today. Not that fridgid.

    Today from cold boiler to a header too hot to touch is about 8:30 mins. I think water capacity of the boiler is around 7 gallons. Any idea if that sounds normal, fast/ slow etc?
  • DIY_GuyDIY_Guy Posts: 38Member
    Correction I gained a full 8 mins by running the pipe open!! ( I was looking at my test numbers from the other main run) Wow, I hope the big mouth will keep this huge improvement in speed!
  • FredFred Posts: 7,853Member
    edited January 4
    You want to let the thermostat manage the room temp to the level comfortable for you and manage the system pressure so that it doesn't get over a pound and a half or so. Outside temps, the size of the boiler relative to the connected EDR and good venting are all factors that affect how pressure builds in the system. Trying to cut the pressure off at 6 ounces, based on a single sampling is not the thing to do. During the dead of winter, an 8 minute heating cycle is not going to be typical and creating a situation where the burner shuts off is not efficient in that the steam will collapse and the mains will have to refill before filling the radiators. If it takes 20 minutes per cycle, in the dead of winter (or longer) let the boiler run until the thermostat is satisfied or it gets to a pressure that is not desirable. Minimize the on/off cycles.
  • DIY_GuyDIY_Guy Posts: 38Member
    Thanks for that insight Fred. The 8 min number was steam to the header then another 4 mins to reach the main vents. It was another 20-30 maybe til the radiators were fully heated and closed and shut down the furnace- for pressure not because room temp was satisfied yet. Seemed like a decent cycle? The apt was not up to temp yet so it cycled a bit to get it to 55 which I had set it at.

    I’m fortunate to have an empty apt for another week or so and I’ll get to move around and retime the mains vents from a cold start and at various outdoor temps to see how it performs.

    Because the radiators gives off their heat even after the steam pressure drops I wish I could tell the boiler to wait 10 mins or so before it refires again , to slow the cycling and give it a chance to release more of it’s heat into the room. Does this thinking make any sense at all? Again I’m a relative newbie to steam so pardon my ignorance... I appreciate your responses
  • FredFred Posts: 7,853Member
    @DIY_Guy , how cold was everything? 8 minutes to heat the header seems a bit long but the 4 minutes from there to get steam to the end of the mains is pretty good. If everything was cold, including the water in the boiler, I suppose it would take that long to boil the water and start making steam. Also, what was the temp in the apartment when you started the boiler? I noticed you said you have the thermostat set at 55, if the boiler had to run for an extended period to bring the apartment up 5 or 10 degrees, and the boiler is a little over-sized, that would explain the short cycling. Leave the temp at 55, steady state and see if it still short cycles.
    I'm not sure stalling the boiler for 10 minutes before it refires after a short cycle will save you much. First, the goal is to minimize the short cycling and second, the time it takes to build steam again and maybe even the need to push air back out of the mains, may in fact use more fuel.
  • DIY_GuyDIY_Guy Posts: 38Member
    Starts have been from a dead cold boiler.

    No exactly sure but Apt was maybe 48- 50? I just set it at a random number, 55, higher than the ambient temp so it would run a while

    I think I’m going to clean the furnace tomorrow and see if it’s gunked up but I think it’s not too bad. I think It was cleaned maybe 18 months ago.
  • DIY_GuyDIY_Guy Posts: 38Member
    What I was thinking of in terms of “stalling” the boiler, is perhaps from a comparison to how forced hot water works: it heats the water to a certain temp then circulates it til either the desired room temp is reached, or the water temp has dropped below the low temp setting. I.e it has given up its heat. Depending on temps, It will circulate for a good deal of time without refiring. What I saw, at least before I went to lower pressure, was once it was as producing steam it would cycle running for 5 mins, rest for 3 ( or however long it takes for pressure to drop) then run again til up to room temp . It seems to me the boiler fires with no regard to how much of the heat/ steam it has just previously made has been released into the dwelling. When my all the radiator are full ( hot end to end ) and all radiator vents closed what is the purpose of refiring? Is it able to force or store more heat in the radiators at that point? In my newbie brain I thought it a benefit to let the radiators dispense of their heat for a while before refiring, especially the way steam moves around rather well at such low pressures.

    One of the college kid tenants came back a week early from his break so it looks like I won’t be able to “play” quite so much with things right now, as it will be running full time again. Though I will get to see how the new vaporstat and big mouth vent help things.
  • FredFred Posts: 7,853Member
    @DIY_Guy , unlike a hot water system, steam collapses very, very quickly. The reason the boiler re-fires, after being shut down on pressure is because the thermostat has not yet been satisfied and the steam has collapsed enough to reduce the system pressure to or below your Pressuretrol's or vaporstat's set Cut-In pressure and refill the system with steam until it reaches Cut-out pressure again. In theory, the Pressuretrol/vaporstat is a safety device. If the boiler is sized to the connected EDR and the Main Venting is adequate, it really should never even engage but that is an ideal set up.
    Does your thermostat typically over shoot the set temp by a degree or more? Mine does not but others have said theirs will. The biggest benefit of the residual heat the cast iron radiators give off, in my opinion is that that delays the next call for heat, which essentially also saves you fuel.
  • DIY_GuyDIY_Guy Posts: 38Member
    Thanks. I can’t say for sure about the thermostat being accurate or not.

    Well, today was a crazy one as I started cleaning the furnace. It was nightmare. I’m doubting the firing chamber was even opened or cleaned at the last cleaning. I busted a firing plate bolt off with very little pressure. I found the chamber liner was completely collapsed inside, and had a good 2-3” of particle build up in there. The gun was firing right into a piece of the liner! The airways were nearly plugged. Not really soot but particle build up. Not sure what that tells me. I’ll post some pictures in next post so you can feel my pain. (Or just get a laugh!)

    So, tomorrow I’ll be off to get a new chamber.

    I’ve also been losing water for a while and having to add. I had not been able to find a steam or water leak anywhere but I think I finally found it: behind the faceplate you’ll see one of the bolts is rusted off- top left. I’d say the gasket failed and it’s been seeping and rusting Behind the cover for some time. Should I attempt to change this gasket? ( if I can find one) Any suggestions? I’m a bit afraid to even touch it in the heating season, I also weld so I could possibly fix the plate, or worst case, fabricate a new one at some point.
  • DIY_GuyDIY_Guy Posts: 38Member
    Feel my pain!🤪
  • FredFred Posts: 7,853Member
    OMG! I think that boiler plate says the boiler was manufactured 2-14-88, making it about 31years old. I really think you ought to consider a full replacement. I'm not sure trying to recover from that kind of neglect is wise or even feasible. Can you see any cracks in the cast iron, in that chamber?
  • DIY_GuyDIY_Guy Posts: 38Member
    I wasn’t really looking for cracks to be honest, so I’m not sure. Interesting about the boiler date, because the slant fin label has a date of 11/93 making the “packaging” of it 25 years old. I have no way of knowing when it was put into service here.

    I just found that plate and gasket in stock and available online. I’ll give the chamber a look over for cracks and I’ll probably give it a go if it looks ok. Although, yes, I can see a replacement in the future. Hopefully just not this week!

  • DIY_GuyDIY_Guy Posts: 38Member
    Got this furnace cleaned up and it’s running well again. I haven’t timed anything yet but it appears to produce steam quicker. I took the opportunity to remove some deadheaded old copper pipe which used to be connected to the tankless pipes and only added clutter around the furnace. I removed the high low sensor for the Tankless and plugged the tap. Also removed an extra water feed that was located next to the skimmer port. This allow me to put the skimmer at 90 degrees.. Also put a back flow preventer on the water feeder line, which this furnace did not have!

    Efficiently and smoke test tomorrow. Waiting for the tankless plate. Not sure when I’ll get to this. Depending on water loss maybe sooner rather than later.
  • DIY_GuyDIY_Guy Posts: 38Member
    > @DIY_Guy said:
    > Pics biggest issue of the day was getting out that top left stud! Ugh!
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