False water line.

fricard

I am replacing a steam boiler. There is one 3” main that goes into an inaccessible crawl space and 2” dry return that goes into the same crawl space. The problem I’m having is that the return is only 17” above the normal water line. There is no space to install a pump or boiler feed tank. I wanted to build a false water line to make up the extra height that I need but I don’t Think it will work because that dry return will become wet and the beginning of the steam main will only be 16” higher than the return at the boiler room. I’m wondering if there is some other solution that doesn’t involve a pump. The new boiler will be a 10 instead of 12 section currently installed. That will gain some space. But I don’t want the left side of the boiler with all the controls jammed against the wall like it is now. I had to change the drain and take apart the gauge glass and it was near impossible.

ted_p

Hi @fricard ,

Welcome to the forum!

I'm sorry that I don't have any answers, but am eager to see what the more knowledgeable folks here post on the topic. The one thing I'd suggest is, if you haven't counted and sized all of your radiation, to calculate the load, and from that determine what size boiler you really need, do so before pulling the trigger. It may turn out that the right size boiler may be smaller than 10 sections, and every additional section you eliminate will save you money and buy a little more space.

In the meantime, I took the liberty of re-posting you pics, so that they appear in-line for easier viewing.

Ted

Jamie Hall

A false water line is a wonderful gadget -- which is to be used if the boiler water line is too low, and somewhere out in the wilderness there is a section of wet return which is higher than the boiler water line, thus making the bottom of a drip or drips dry and allowing steam to bypass.

That is not your problem. Your problem -- which is a little unusual, by the way -- is that the boiler water line is too high in relation to the piping, not too low.

Now. What to do about it. I'm sure others, with more varied experience than I, may have some ideas. However -- assuming that there is no way to lower the boiler water line, or select a shorter boiler -- the simplest is also the most obvious: select a pressure limit which won't back the water up into that dry return.

In this situation, first you need a vapourstat, not a pressuretrol. Then, having gotten the correct control, set the cutout for 8 ounces per square inch (the dry return may flood at 10 ounces per square inch) and the cutin at 4 ounces per square inch. Verify the pressures, by the way, with an accurate gauge.

If you could find a Hoffman Differential Loop and pipe it into the system correctly, it would be a good backstop for the vapourstat -- it wouldn't let the pressure differential between the boiler and the dry return get over 8 ounces, as it happens. But that is probably more trouble than it's worth.

fricard

Hi Ted,
I have already sized the boiler. Thanks for reposting the pictures.

fricard

Hi Jamie,
The boiler sits in the pit on the floor. No blocks or anything. So I don’t think we can lower it anymore. I actually do have a Hoffman Differential loop hanging up in my shop that has been there for about 15 years. I would prefer not get into trying to install that. If the solution is as simple as just installing a vaporstat then that is what I’ll do. It’s a one pipe system. Can I heat a one pipe system at 8oz? I’ve only used Vaporstats on vapor systems.

Jamie Hall

One pipe? Hmm. Yes, you can heat it perfectly well at 8 ounces. Shouldn't be any problem at all, although you may find you need to adjust some vent sizes.

However, I'm inspired to ask -- where are your main vents? If that dry return is actually purely a return line -- the main vents are out in the wilderness somewhere -- then it's a little less critical as to whether it floods or not. You still don't want it to -- the boiler water level would drop a good bit if it did, which could well be a hassle -- so keeping the pressure down is still the way to go. But it's not the nightmare it might otherwise be.

Don't junk that differential loop -- someday you will hit a job when it's exactly what's needed!

fricard

There is a very undersized main vent at the end of that return. I don’t think it’s in any of the pictures. Thanks

retiredguy

I always hated working in a pit due to having limited access for service and repair and concern for my safety and that of all others after me. Having said that , I would rather, if possible, set the boiler above ground and install a condensate or condensate feed pump in the pit. I realize that I would be adding 1 more piece of equipment that is a potential for service and failure of the system to operate free of any problem but working in a pit always bothered me. I have seen too many accidents happen in an area of limited escape. my 2 cents

EBEBRATT-Ed

Agree with @retiredguy on this much more room for service you can work on it like a human, Put a small condensate pump where the boiler sits,

Only issue may be getting to the chimney with the flue

fricard

The flue pipe would be an issue but also if I took the boiler out of the pit the steam main would be lower than the boiler.

Jamie Hall

fricard said:

The flue pipe would be an issue but also if I took the boiler out of the pit the steam main would be lower than the boiler.

Actually that can work -- though you wouldn't think it would -- provided that first, there is a really good header arrangement on the boiler (no shortcuts there, thank you -- plenty of height on the risers, then over and a drop header, then down from there) and provided you have generous drips to the wet returns.

Which, obviously, would go to a receiver, and then a boiler feed pump (not a condensate return pump). I would have the feed pump output come into a short wet return, then a Hartford Loop -- as well as having, obviously, a check valve -- not directly into the boiler. You might also find that an outboard extra water tank -- with a large surface area at the elevation of the boiler water line, equalized to the boiler and tied into that short wet return, might be needed to stabilise the boiler water line.

EBEBRATT-Ed

@fricard

Steam mains can go down as long as they are dripped as @Jamie Hall mentioned the condensate receiver or boiler feed tank will be there to drain into

nicholas bonham-carter

I would suggest a gravity return, with a vaporstat controlling a hi-lo-hi gas valve, with extremely generous main venting.
Pipe it for extremely dry steam-don’t skimp on the pipe sizes!
Is this system parallel-flow or counterflow?
There is a possibility of the main vents being flooded with water above 9 ounces pressure.—NBC

fricard

Parallel flow.

gerry gill

Just remember to ‘calibrate, the vaporstat on a test rig. They generally suck coming out of the factory.

BobC

The old mercury bulb units had much better quality control, the new ones have NONE. You do have to make sure mercury bulb units are level when hot.

The Steam Whisperer

If that dry return is pressurized, like it usually is on a one pipe system since it is the end of the steam main, that you really don't have a problem or at least not much of one. That would be an A dimension, not a B dimension. The return line should be pressurized within 1/2 lb of the supply when the system is running at full capacity with the supply at 2 psi., that 1/2 psi of differential will only back up water 14 inches. Just make sure the boiler is properly sized to the radiation and don't operate the system over 2 psi. I have found most systems run at much lower pressure that than just fine ( piping is usually oversized and/ or radiation has been removed), so you can often run at only a few ounces of pressure and heat just fine.

dopey27177

If I am seeing the steam main correctly and at its full length it is not insulated.

Un-insulated steam piping causes a lot of condensate. That condensate has to be replaced by hand or an automatic feeder.

To see if part of your problem is caused by excess condensate run out shut off the auto feeder and see what happens when you fill the boiler manually.

When you fill the boiler manually set the height to what you feel is proper for the boiler and see what happens.

Typically, during the heating season if the system is reasonably tight you may need to fill the boiler every 3 to 6 days.

Once this is done I believe once you insulate the steam mains and excess condensate is no longer generated your boiler should operate at the normal water level with auto feeder in service,

Jake

motoguy128

fricard said:

Hi Jamie,

The boiler sits in the pit on the floor. No blocks or anything. So I don’t think we can lower it anymore. I actually do have a Hoffman Differential loop hanging up in my shop that has been there for about 15 years. I would prefer not get into trying to install that. If the solution is as simple as just installing a vaporstat then that is what I’ll do. It’s a one pipe system. Can I heat a one pipe system at 8oz? I’ve only used Vaporstats on vapor systems.

If the header is large enough (it’s 3”, so if the boiler is 300k or smaller, it was probably a Vapor-Vacuum system to begin with anyway), then all you need is to slow the radiator venting and dramatically increase the main venting and it will pour like a kitten. If done right it may run at nearly 0oz, the vacuum generated at the head of the steam And natural upward pitch of the pipe draws it forward.

Mine worked great that way. 3” main, around 650 installed EDR on just a 200k boiler with some TRV’s on about 1/3 the Radiators. Previously it had a 375k boiler with about 700EDR And ran at around 3-4oz... without an equalizer Or drop header, single supply off the boiler. Added more main venting when I installed the new boiler and slowed radiator venting even further.


But again, it may require replacing almost ALL of your radiator vents with very, very slow vents. #4’s for most maybe #5‘s on the largest and Ventrite’s to cover those That fall between 4 and 5. The system was an unbalanced mess with A mix of 5’s, #6’s C and D’s. While proportional to radiator size plus length of the riser and lateral, so in theory it should have been balanced but it wasn’t. PRessure was higher with faster radiator venting. That;s right, with more venting, my pressure was higher. Why? Radiator didn’t heat up fully or evenly so steam was not consumed as fast, therefore when the consumption of steam was lower than the supply of steam, pressure went up until it reached equilibrium again. As pressure goes up steam velocity drops, and radiator heated up more evenly again.

Oddly, vent size becomes less critical From what I can tell and lateral size becomes a step limiter. Radiators on smaller laterals will vent slower as vapor is more restricted. So a smaller radiator on a 1” lateral will heat up proportional to a large one on a 1-1/2” lateral with only a slightly larger vent.


Let me repeat one key element here. Pressure building up in a boiler is partly due to an imbalance of steam consumption compared to steam supply. Think of a traffic jam. One solution is to tighten the spacing and speed up the cars. But another is to widen the roadway at the pinch point. Maybe it’s a very narrow lane, two cars well coordinated can pass at 30mph, but at 35mph it drop to one lane, but cars can’t get 45 going through it while narrowing to one lane. Two cars at 30mph is more capacity than one at 45. SO going slower, increased capacity because it further utilized the lanes.

The only time pressure should be necessary in a steam system, is if the main or laterals are too small (builder saved money) or if higher temperature is needed because the radiators are too small. OR if the building is very very tall.