What main vents for single-pipe system?

Motorapido

I plan to replace the main vents in my 80-year-old single-pipe steam system. From the looks of the vents, they are probably original to the house. Dunno.

I've already checked and adjusted all radiators' pitch so they have a degree or two pitch back toward the shut-off valves, and have replaced all radiator vents with like-sized vents (the ones I replaced were all ancient and noisy). I still get a little water hammer and slightly uneven heating. I figure it's time to replace the main vents.

Boiler is about 6 years old. Burnham. Gas. It appears to be very well installed, with 24 inches from the boiler top to the steam header pipes. Headers and all steam piping is insulated. Pressuretrol set to 0.5 and 1. All steam pipes now insulated with at least 2 inches of insulation (insulation on one section of steam piping had been completely removed, but now I have it all properly insulated).

I can't see the manufacturer name, model number or size on the vents. I'd like to order new main vents before removing the old vents. House is two-stories, brick and plaster, 1920s. As a rule, should I replace those main vents with identically sized main vents? To do so, I will need to somehow read the manufacturer name on the old vents and any sizing info, and they are both badly corroded and tucked up in dark recesses. Or can somebody recommend a general replacement for them without me knowing the make and model and size? Is bigger always better in return vents?

At the end of one branch steam line, before it transitions into thinner condensate return pipe, there is a nipple that rises about 2 inches off the steam pipe, and a vent sits at the top of that nipple (that's at the end of a steam line that is a branch off the main line). On the other main end, which is essentially the main-main, a vent is threaded into a union that sits flush with the top of the steam main. Why the vent on the end of that branch of the main is elevated and the vent at the end of the main-main is not elevated is beyond me. So while I am asking questions, would it be a good plan to elevate the currently-unelevated vent with a 2-inch nipple when I put the new vent in? I have plenty of working space to elevate it on a nipple.

I realize that I must be patient and apply penetrating oil over several days and also apply some heat to the female portion of the vent fitting, and use two wrenches, to prevent breakage upon removal. I have extensive mechanical skills and experience in separating old, stubborn, seized fittings in many other types of circumstances.

By eyeball, the mains and returns all seem to be properly pitched. There is no evidence of sagging of pipes, and the structures in walls and floors do not seemed to have sagged noticeably anywhere, so I assume that the pitch of the mains and returns is appropriate.

Finally, while I have those two vents removed, would it be a good idea to pour water into the openings after opening the floor-level condensate-return valve back at the bottom left of the boiler exterior to gently flush out any corruption that is likely in those lines? I have regularly drained water from the low-water cutoff valve until the water runs clear each time, but I have not yet drained the condensate return line.

Thanks in advance for any suggestions. What an excellent forum this is.

Fred

Main vents should be sized to vent all the air out of the mains as quickly as possible. Usually, old vents are not adequate in size because they were installed at a time when the system was fueled by coal and the fire was maintained almost throughout the winter months. Steam filled those mains almost constantly and little air had to be evacuated after the initial removal. Today's gas/oil fired boilers cycle and air enters the mains after each heating cycle which calls for frequent evacuations. Getting that air out quickly saves fuel cost and also minimizes system pressure that results from longer heating cycles. You should measure the length and diameter of each main and post that info here and we can suggest the best vents to use.
Also, if you can flush the wet returns out, that would be a good annual maintenance effort as well.

Motorapido

Thanks, Fred. I'll measure this evening and then post info. Meanwhile, about flushing, is pouring water -- just gravity fed, poured out of something like an indoor plant watering can -- sufficient, or must I attempt to rig up a fitting at the end of a garden hose that I could screw that into the NPT fitting where the vent was removed, to flush under the pressure of the garden hose? I was thinking that pressurized flushing might be too aggressive, or might push sediment and old crap up into the boiler incoming water line. Thoughts on this?

Fred

Are there any drains or plugs on the wet returns near the floor? Is there an isolation valve on the Hartford loop or pipe going into the boiler that would allow you to close off and isolate the boiler while you are flushing that wet return? Gravity fed water from a container won't do the job and you do need to hook a garden hose up. That may allow allow some of that crud to enter the boiler. This may be a job you want to handle at the end of the heating season, and then do a complete wet return and boiler flush.

Motorapido

Thanks, Fred. At the very end of the wet return, after it has dropped to straight-down vertical, it joins the Hartford loop, and above it the water inlet pipe flows into the boiler. On the floor, there is a garden hose spigot. If I would open that with the whole system cold, I imagine that a small amount of condensate would flow out. There is no shut-off valve that would allow me to isolate the cold return from the Hartford loop or the incoming fresh water pipe feed. So if I wait until the end of heating season and attach a garden hose to the cold return lines at the fittings for the two main vents, one at a time, and the hose pressure forces rusty water with sediment and rust flakes into the boiler, will I risk permanantly clogging the boiler or damaging anything? Like you say, I could then just open the water inlet and open the low-water cut-off outlet valves and flush clean water through. Any danger in that? Also, when I would attach a garden hose at a main vent fitting to do the flushing, I imagine that some water would back-flow into the steam mains. Would I risk pushing crud up into the mains and even up into the radiators, where that could cause problems or even clog radiator vents?

Fred

No problem with backing crud into the main. It's all down below the water line. Don't use you Low water cut-off valve to drain the boiler. There should be a drain valve somewhere along the bottom of the boiler itself. That runs into a mud leg in the bottom of the boiler that traps crud that settles in the boiler. Use that valve. There will be more water in those wet returns than you may think so put a hose on those wet return spigots and run it over to a floor drain, then open the spigot and run clean water into that Vent opening at a rate that allows it to stream out of the floor spigot without running into the boiler. You may find that both the floor spigot and the Boiler drain don't drain when you open them due to a buildup of crud in the valve. If so, run a wire into those valves to open them up.

Motorapido

Fred, good stuff. Thanks. Perhaps I am mis-naming the draining device that I have been using to drain 5 or 10 gallons of water from the boiler monthly. It is a black casting piped to the side of the boiler that also has the pressuretrol and the 0-30 psi gauge and the water level sight tube. A wire runs from it and attaches to the wire harness at the pressuretrol, and that wire bundle then goes inside the boiler to control the gas flame. The black casting has a big ball valve handle on it. The casting is about 6 inches off the floor. Isn't that the valve I would use to drain/clean out the boiler? The only other valve is the hose spigot valve on the other side of the boiler where the wet return lines drop to the floor.

Fred

The valve that is 6" off of the floor sounds like the correct valve on the boiler but you've got me really confused about the other stuff. Typically the Water sight glass, the Low water cut-off and the Pressuretrol are off of a different tapping that is about 18 inches off of the floor. The Pressuretrol itself certainly should be above the boiler's water line. If you have all that stuff off of a valve that is 6 inches off of the floor, you need to post a picture so we can see what is going on there???

Abracadabra

@Motorapido pics?

Motorapido

Fred said:

The valve that is 6" off of the floor sounds like the correct valve on the boiler but you've got me really confused about the other stuff. Typically the Water sight glass, the Low water cut-off and the Pressuretrol are off of a different tapping that is about 18 inches off of the floor. The Pressuretrol itself certainly should be above the boiler's water line. If you have all that stuff off of a valve that is 6 inches off of the floor, you need to post a picture so we can see what is going on there???

I might have described it incorrectly. As I face the front of the boiler (where the access panel is to the burner), on the right panel of the boiler there is a pigtail above the waterline that has the pressuretrol mounted on it. A few inches away is a 0 - 30 psi gauge that is nearly flush mounted to that panel of the boiler (I imagine that it is on a nipple that goes inside the panel, and perhaps a pigtail behind that (not sure how those gauges are set up internally). Then toward the back of that right-side panel of the boiler, is the sight glass, and behind and below that -- below the water line -- is the low water cutoff.

Fred

That sounds better. There is no pigtail behind that gauge that is flush mounted on that panel. Those gauges typically have a built in syphon. Do as I suggested above, as far as flushing the wet return. You should be fine.