Main Vent Sizing Question

Bobby D.

So a main vent question for all you walleys who have helped out in the past.



I have a one pipe steam system with an insulated 2" Main, that is 30' long.



3' from the end of the main is the vent riser ( see photos ) and is reduced from 1" to 3/4" to accomodate the Hoffman # 75 Vent, which gets warm but does not vent or spit or anything.



There is 9" between the Main and the bottom of the Hoffman 75.



Changed out all the radiator vents to Hoffman # 40 in the fall. Don't know what the problem is but I am getting wet steam.



The pitch is ok on the radiators, mains insulated, water fairly clean, other than some rust. I still get a surging water line in the gauge glass. The new Hoffmans hiss constantly and never stop. Is boiler overfired ?



The main vent Hoffman 75 only gets warm. Pressuretrol is set to cut in @ .5 and out at 1.5 psi have 0 - psi gauge on pigtail T with Pressuretrol.



I think the main vent is shot, ordered two Gorton # 1 Air Eliminators, want to know if the main will be over vented, or under vented or just right. Basically how much main venting do I need ?



If two vents are needed I would line them up in an antler arrangement, as you can see the space is very tight the Hoffman # 75 is right against the floor boards.



Also considering replacing all Hoffman 40's on the radiators to Gorton C's or D's.



Thanking you all in advance

Wishing you all a very Happy New Year !



Bobby D.

BobC

Questions

30 ft of 2" main is about 0.66 cu ft of air that you have to handle, The Hoffman is rated at 0.75CFM while the Gorton #1 is 0.5CFM. Either one will be able to vent the main in about a minute. You might need more venting on the radiators but lets sort some other stuff out first.



Have there been any other changes to the system other than the new radiator vents? Did it work like this last year?



What king of boiler do you have and is the near boiler piping correct? Is all the piping in the basement insulated? Post some pictures of the boiler from a couple of angles so we can see the piping above the boiler and any other piping that goes to the boiler.



What kind of thermostat are you using and is it set up for a steam system? It should be set for 1 cycle per hour, the new programable ones come set up for hot air and default to 5 CPH.



How much is the water jumping in the glass? Can you see any signs of water droplets above the waterline in the glass?



If the boiler water is dirty and jumping around a lot I would start by flushing and then skimming the boiler so you have good clean water to deal with. That can take the better part of a day so you might want to wait for a somewhat mild day for that.



Bob

Bobby D.

More information on this question

Yes it worked the same as this last year, I thought changing the radiator vents from Maid O' Mist's to Hoffman"s would help. The Maid o Mists also spit water, hissed never stopped venting.



I have an old Dunkirk boiler Model 717,( see photo of front plate) which I believe was a coal fired version that was converted to oil ( not 100% sure of that) either way I know I need a new boiler, not in the budget.



Piping photos show only single riser although there are two top ports.

If you need any other details of piping let me know.



Thermostat is set back type Lux 500 which also has an ac control function.

I do not have central air, if you know I need a new boiler do you think I have central air. I do not know the CPH cycle on this unit but will try to find out. Maybe I can set the CPH on this model.



What model thermostat would you recommend ?



I just hot skimmed flushed it a bit ago. Water and steam that came out seemed only rusty, sight glass water pretty clear.



Water moves up and down 1 to 2 inches, bounces up and down.



Yes there are and were water droplets above the water line in the sight glass.

Bobby D.

Follow up

Just posted photos and facts on your questions

BobC

Pigtail ok?

I see a couple of things that might be a problem. The steam header should be 28" above the normal water level and the Hartford loop (in the back) is usually a couple of inches below the normal water level. However that is with modern boilers which yours ain't. You don't happen to have the install manual on that do you?



I have a Hoffman 75 on my main and it gets blistering hot in about 9 minutes (my main is only about 12 ft). If yours never gets hot it may not be opening and the Hoffman #40's will take forever to vent the 0.66 cu ft in the main along with the radiators. One thing that will kill a vent is high pressure so you want to be sure that isn't a problem before putting on a new main vent.



Does the boiler ever shut down on pressure? If it doesn't your pigtail could be blocked so the pressuretrol and gauge are not seeing the trues pressure inside the boiler. To test it you have to unwire the pressuretroll and then remove the pressretrol and the gauge; then take the pigtail off and clean it out and make sure there isn't any crap in the boiler tapping. If everything looks clear your 0-30 PSI gauge might be shot. Is the gauge besides the pressuretrol a 0-30 or is it a 0-3PSI? If it is a 0-3PSI, what does it read?



You said you flushed and skimmed did you drain the boiler completely before skimming? Your right about the water being pretty clean but there might still be some oil in it.



All of that piping really should be insulated, you can just wrap it with 3" bat insulation for now - not pretty but it does work.



Let us know how you make out,



Bob

ryanr256

Lux 500

I have that same thermostat. No CPH setting that I could find, just a "swing". I have mine set for a 2 degree swing with no setback.



I've attached the manual for the 500. Hope it helps.



I also have Hoffman 75 main vents. Mine get so hot you can't touch them. Before that happens, you can hear the air escaping. It's not very loud, but it is audible.



-Bob

Bobby D.

Follow up

Boiler always shuts down on pressure, the gauge is 0 to 3 PSI cuts in at .5 PSI and out at 1.5 PSI . and matches Pressuretrol settings.



I can disassemble Pressuretrol to check pigtail to make sure it is not blocked, and check the boiler fitting as well.



No I have not completely drained the boiler before skimming.



Over the summer I flushed the wet return and drained and refilled the water several times, I think you are right there is still oil in the water. Sections of the wet return were replaced several years ago,



What about the CPH Thermostat issue.

BobC

Test for boiler water

A quick test for your boiler water would be to drain off a quart or so and boil it on top of the stove (just don't let the wife catch you) and see if it looks kike plain boiling water.



I took a look at the manual ryan256b posted and it looks like it may not be suitable for steam. As long as it doesn't try to fire the boiler many times an hour you might be ok with what you have, I assume ryan256b is using it on his steam system so it should well be ok.



Do you have another thermostat you can throw in for a test? I have an old Sears analog with a clock that switched between mercury bulb A and B for the setnack (1981 I believe). I do have aHoneywell 6450 on order, we'll see how that works out.



Bob

Bobby D.

Boiler Water / Tap Water Comparisons when boiled

Here are some photos of my boiler water ( boiled on stove )

and tap water boiling.



There is a big difference between the two.



Boiler water has noticeable oil sheen on surface, and produces very large bubbles, with little or no steam mist. Also noticeable scum like surface on water when about to boil.



Tap water, produced small tornado like spirals of bubbles with lots of mist enough to fog lens and no large bubbles.



Think the problem is oil in water in boiler,



What should I do ? Many wall posts recommend using Squick and skimming etc.



Any suggestions appreciated.

BobC

Boiler water

If that 0-3 gauge is reading and agreeing with the pressuretrol we'll assume that area is fine for now. we'll let the thermostat issue rest till we get that boiler water sorted out. It looks like you have oil in that water and you have to get past that issue first..



I would be leery about adding chemicals unless you really have to. Since you just skimmed it, I would drain that boiler completely and refill it with fresh water, in fact do that twice. Next run a nice slow skim that takes and hour or two to fill a 5 gallon bucket and repeat that a couple of times. Then fire it up and allow it to run for a day or two and retry the boiling water test.



Repeat that until the boiling test looks a lot more like regular boiling water. I'm sure the pro's will pipe in if they have a better idea.



All of this takes time so put a comfortable chair next to the boiler. Once the water is clean we'll take another look to see what else has to be done.



Bob

ryanr256

Thermostat

I guess ignorance is bliss.   We bought this one without knowing anything about the differences between scorched air and steam, as far as thermostats go.



Now that I'm educated, I can say we got lucky. This one works with steam. It trips on temperature and that's it. No cycles, no fancy stuff. We use natural gas and I've set the switch to be gas. I don't know what would be done for oil.



Since I've been reading The Wall, I've set the swing to be 2 and eliminated the setback we were using.



So, in essence, it does work with steam.



-Bob

Bobby D.

Drained Skimmed Filled and Drained & Skimmed....

Over the last day or so I have skimmed the boiler and slowly feed the boiler, off a skim drain on the side of the boiler.



Then I fired it up to full steam, till shut down, blew it down, on resteam and repeated this procedure.



The gauge glass water is now very clean with little or no bounce during steaming,

( however there is condensation in the gauge glass, and the glass needs to be cleaned on the inside because of residual rust & grime in the upper portion.)



I replaced all the radiator vents with Gorton D except for a small room just above boiler that got too warm, there I put a Gorton C. The main vent is unchanged as a Hoffman 75.



Now cycle times and controls, the boiler reaches full steam and shut down in about 45 minutes on a dead cold start, then cycles off after reaching 1.5 lbs pressure and restarts burner when pressure drops to .5 lbs usually within a few minutes of shutdown. This repeats over and over until room temp setting is met.



Which made me wonder why the burner is going on and off and on and off etc



Is this short cycling ?



Is the boiler overfired ?



If the burner is slightly downfired would the on off cycle decrease.?



Is'nt there a cycles per hour control thermostat that would say do this cycle only 2 or 3 times per hour. So I would not be burning oil off and on and off and on until temp is met.



Maybe I need some clarification on this whole cycles per hour setting on a thermostat.



If you read above I am currently using a LUX 500 thermostat that is programable.

I am doubting that letting a steam boiler shut down for the night and doing a cold restart is more efficient that letting the pot simmer at night.



Many thanks in advance for any input or thoughts.



Happy New Year !



Where is Maddog ? has he been banned from the Wall ?