Two pipe with vacuum air vents?

Gary Elovitz

I came across the radiator in the photo - it is a two pipe radiator with angle valves on both sides. The supply is 1", the return is 3/4", with an air vent. There is also a skinny tube that comes up to just below the air vent - I am guessing that at one point that tube might have been connected to the air vent. The building is 6 stories, in the Back Bay area of Boston, built in the late 1800s.



The original boiler is long gone, and the near-boiler piping has all been "updated", so I can't get any clues there.



The system does not work well at all as is. I would like to understand how it was originally intended to work so I can look into options to get it working properly again.

If anyone has any ideas about what we have here, and especially if you can point me to any diagrams that show how this type of system was originally put together I would be most grateful.



Thanks!

Steamhead

This was an "air-line" system

where an exhauster of some sort pulled the air out of the rads thru special vents. The Paul system was the best-known of these, but Eddy and others made these systems too.



What kind of problems are you having with it?

nicholas bonham-carter

Paul system problems

Are you able to see the basement piping layout, or is this a condominium situation where you can only deal with this apartment? If so, it reminds me that the condo regime should always treat the steam, or water heating system as part of the common are, like the roof, or hallways, and forbid any changes to be made in individual units, without the supervision of a steam expert who knows the system.

When the airline feature was discontinued, what arrangements were made to allow the air to escape from the whole system? Were any main vents put in the returns, or traps?

The system air will not be able to escape in a timely fashion with just the radiator vents, because the resistance is too high. Check and see if any vents were put in the tops of the risers, as 6 stories of pipe contains a lot df air!--NBC

Gary Elovitz

Thanks

Thanks for the responses. I am just getting started on this system, so I don't know much yet. I know that some radiators get plenty of heat, while others never get steam. Some of the old distribution piping in the basement is exposed and some is buried above plaster ceilings. The vacuum pump or exhauster is long gone. I will be looking at the entire system (not just one unit), and I want to get an idea of what the system was supposed to look like in order to figure out how to salvage it.

ChrisJ

Vari-vent

I sense a heat timer vari-vent problem.



Though I know absolutely nothing about vapor systems I do see one on your radiator and they are known for causing this problem.

MDNLansing

Basic Pincipal

The basics behind these systems are simple. Steam enters the rad via the large pipe and air escapes the radiator through the second line. Condensate that accumulates in the radiator returns via the steam pipe like a single pipe system. All the air lines connect together into a loop that follows the mains and it has a single point to vent. So all the radiators vent to a large vent in the boiler room and not into the rooms themselves.



It looks like someone has disconnected the air lines and installed a second pipe at the bottom of the radiator to return the condensate to the boiler. It's a shame too. I have an old air line system installed in 1907. I just restored all the components and fixed a few things up and it runs great. I'm able to draw 10" of vacuum with no mechanics or moving parts.

Dave in QCA

Early 2-pipe vented system

I am seeing something a bit different than the previous responses.



First, I note that the size of the supply to this radiator appears smaller than what would be the norm on a 1-pipe system. The valve sizes to appear to be normal sizing for the very early 2-pipe vented systems that were common in the 1880s. This type of system, installed long before the invention of the steam trap required an air vent on the radiator and the second pipe was essentially a drip leg. My guess is that the vacuum vent apparatus was a later modification that was later abandoned.



2-pipe vented systems have a pretty normal steam main and distribution except that the sizing of the risers and radiator supply valves is usually at a least one size smaller than what you see in a one-pipe system. The second pipe is smaller, often 3/4" and occaisionally 1/2" on a small radiator. This outlet is always valved. The outlet pipe in this type of system carries away the condensate but not air. There is no way for these returns to vent, as they usually run from the outlet of each radiator down to a wet return line. In an ideal installation, each radiator will have an independent drop to the wet return in the basement, however I have seen some where return lines from more than one radiator were tied together, and this is the reason that the outlet valve on the radiator is necessary as it is completely possible in this case for the return line to become charged with steam. This type of system does not have a B dimension because the return line does not run at atmospheric pressure, but rather it is in balance with the rest of the piping.



I strongly suspect that the vacuum vent (paul, eddy, or ?) was a later addition intended to improve the operation of the system and add modulating vacuum control..



For these types of system to operate properly, slow radiator vents are a must. The Heat Timer Vari-valve that I see on the pictured radiator is a sure way to reek havoc in a system like this. I would recommend vents no faster than Hoffman #40. I suspect that once your vents are balanced with slow venting, that the rest of the problems will vanish. If not, you may need to add riser vents if they are not already there. Mains also need to be vented, and preferably vented FAST. I

mcsteamy

Dave,

I think you hit the nail on the head with respect to what happened.  It's rather improbable that someone came along and added additional valves--it is far more likely that they added the vacuum vents later to upgrade a former state of the art early two-pipe system to the new state of the art.  When a Paul system works, it's great.  When the boiler fires, every radiator gets heat almost immediately, at the same time with no noise, no whistling, no spitting vents.  This one someone apparently didn't know what they had, and pulled it apart.  I'd guess the two pipes do little more than keep condensate keep condensate out of the primary steam-carrying pipe.  With six stories, I doubt each drops to a wet return!



I don't know that I would blame the bad distribution on the varivalves.  It really isn't their fault, unless you can blame them for hogging steam and being really, really hard to compete with vis-a-vis the main vents if tenants run them wide open (which they will).  I've always used them on the end-of-loop radiators, and they do a really nice job in that application.  Closed down, they perform fairly close to a normal vent.  The problem is keeping them that way, which won't happen in a rental once  tenants find the magic "heat lever". 



I wonder if you could just burn all the money here on main vents, and then put on cheapie Home Depot Chinese adjustable vents.  If there are Varivalves everywhere, that's going to be just a ton of money on vents in a 6 story apartment building.  It isn't as if the $6 Chinese jobs don't work--they just vent poorly.  But it sounds like that's what may be called for here.  Tenants will still think they have an adjustable vent, even if they really don't.... Alternatively, you can pick up Hoffman 1As for about $17 rebadged as a Legend T-60A.



As for a condensed version of what it is, I would treat it as a rather odd single pipe system which theoretically gives you the ability to throttle down a radiator by using the inlet valve--if you can tell which one it is...

Dave in QCA

2-pipe vented, short comings

The problem with 2 pipe vented systems, is if the return connections do not go independently to a wet return, and they probably do not, shutting down the supply will not necessarily shut down the radiator. This is because steam from one fully heated radiator can enter the return piping and flow backward into another radiator through its return pipe. That is why there are 2 valves. To shut down one of these radiators you have to shut both valves.



From my experience on of these old system, a contractor had installed a new boiler and when doing so installed new Hoffman 1A vents on all of the downstairs radiators. Then when I got involved, it was to try to make a radiator in the dining room, where the thermostat was located, get some steam. No matter what I did it would not heat. I even disconnected it from the valve looking for blockage in the steam valve. Nothing. After reading some information on this site, I went back and closed all of the 1A vents very carefully to setting 2. You have to take the caps off and look at the top because they are so sloppy that 2 could be fast or slow depending on whether or not you have the adjusting wheel centered. Once all the venting on the rads were slowed down, the system worked just fine.

Over venting of a cold radiator will cause it to allow steam to enter way too fast and once that happens, the cold iron will continue to suck in more steam. This can end up stealing much steam from other radiators causing the system to be way out of balance.

Gary Elovitz

Thanks for the input

You've given me a lot to think about as I start digging into this project.