Schematic of Mystery 2 Pipe System without Traps or Vents = How Does it Work ?

radcon

I'm attaching a schematic of my 2 pipe system. How does it work?
I'm still at a loss as to how this system has operated for 90 years without vents or traps in the supply & return piping. There are fittings with plugs at the ends of the 1" dry return branches and the 2" supply branches where they reduce from a 2" supply to a 3/4" (run out?). Those fittings are close enough so an F & T trap could be installed between the supply and and return. However, there is no sign that the plugs have been disturbed or had a wrench on them since they where installed. The finish and patina match the fittings. Also, one of the 1 x 3/4 ells on the dry return would have to be tightened another 20 deg. to be vertical and useable.
Instead of using a connecting trap between the supplies and returns the installers ran 59' of 3/4" insulated pipe and 47' of 1" pipe, plus fittings and hangers. Thats a lot of material and labor and for what? The attached schematic shows the layout and sizes and height above floor so the slope of the pipes can be checked. The dry returns slope toward the boiler, the supply piping slopes away from the boiler, and the wet return on the floor is level.
My guess is the 3/4" pipe would relieve the air and excess steam/condensate from the end of the 2" supply lines and empty it into the 1" wet return to the boiler. I can understand the condensate going through the wet return but where does the air go? Does it get pushed through the return and up the riser and back into the supply piping?
I've been doing a lot of research and haven't found a 2 pipe system like this one. Any Thoughts?

Tinman

Awesome drawing! Do you have a picture of the fitting on the opposite side from the radiator valve?

Tinman

There's probably orifices on the inlet or the outlet of the radiators.

JUGHNE

Pictures of valves and outlets of rads would be good.
Also the piping around the boiler, especially the returns with the check valves.

radcon

I should have been more specific the no traps or vents applies to the supply & return piping. The radiators all have Hoffman Adjustable Modulating Valves on the supply side and Hoffman No. 8 Return Line Valves on the return side. The No. 8's were rebuilt 5 years ago, and the supply valves are all stuck in the open position. All the radiators heat fine. I'm attaching photos of the piping at the boiler and at the ends of the 2" supply.

radcon

Here's photo's of what I believe are check valves. The Lunkenheimer is on the wet return, the Fairbanks is on the dry return.
We bought this house in 2000 and had lots of hammering until the No. 8's were rebuilt. And at some point I noticed there were no vents and remember hearing "vent the highs and drain the lows" so I had a vent installed in the dry return in the tee where it drops down by the boiler. The steam guy put in a Gorton Air Eliminator No.1 V on a 12" piece of 3/4" pipe screwed into the tee. I don't recall that it made much difference one way or the other.

Steamhead

With those Hoffman components, it looks like your system originally had a Differential Loop. That's where the air vent would have been. The Loop was probably removed when the knuckleheads replaced the boiler. I know of cases where these systems were run at high enough pressures that some steam got to the radiators by compressing the air, but that was extremely wasteful.

If the radiators are "heating fine", there HAS to be an air vent somewhere. You probably haven't found it yet.

radcon

Thank you Steamhead - I'll look up Differential Loop. The only vent is the one I asked to be installed in the dry return. I've looked this system up & down but I'll go over it again, look for vents, and post the results.

sreja

We have a 5-story 14 apartment two-pipe system and a dry return feeding to a condensate pump, and only one vent, at the dry return, (none on the radiators) and it works just fine.

JUGHNE

You are venting air thru the condensate pump. Often that is the only air vent on a pumped return 2 pipe.

Gordo

@radcon :
Could you post a picture or two of your Hoffman Adjustable Modulating Valves? Thanks!

radcon

Just to be clear my 2-pipe system does not have a condensate pump.

radcon

Photo's of Hoffman Adj. Mod. Valves on two radiators.

Steamhead

Based on the radiators and the valve bodies, I'd say that system was installed in the mid to late 1920s.

radcon

Yes, Steamhead, our home was built in 1928. And very well built, I would say.

radcon

Eureka! Mystery solved. Thank you Steamhead. You thought my system might have had a Differential Loop. So I looked up Differential Loop in my copy of "The Lost Art of Steam Heating Revised" in the index and it referred me to pgs. 399-392, 432. The Diff. Sys. on pgs. 399-392 looked like a maybe, then I went to pg. 432 which described a Hoffman equipped system, which seemed closer but very complicated. So I looked at the next couple of pages and there it was, MY SYSTEM. Almost. My system is identical to the ARCO Model K Vapor Orifice System except instead of controlling the supply steam via an adjustable orifice in the supply valve my system controls the steam with a Hoffman #8 thermostatic valve on the return end. The schematic on page 436 is piped identical to my system, except the "air eliminator" is called a vent. It said you have to keep the boiler pressure very low since there is no boiler return trap. I checked my Pressuretrol and the cut in is .5 and the differential is 1 for a cut out of 1.5 lbs. So that's why it works. I could have sworn there was no vent in the system when we bought the place, but
I must be mistaken. I do know that I asked for and got the new vent shown in the photos. I'm sure I'll have more questions in the future, so stay tuned. I'll be getting a new boiler ASAP (we had snow flurries this morning) since our existing one is working only because I did a patch job on one of the sections where corrosion had eaten through the casting.
Thanks again everyone for your interest and recommendations.

Jamie Hall

Chances are that those Hoffman inlet valves are adjusted to fit the radiation. They can be -- and should have been but that didn't always happen (the Dead Men weren't infallible!) and if they are, they act just like orifices. With that arrangement, if you keep the pressure down where it belongs, it should be very even and that one vent, believe it or not, is probably quite adequate.

Best way to find out is to put a good low pressure gauge on the system -- 0 to 3 psi -- and watch it as the boiler fires from a cold start. What you should see is the pressure should rise as the boiler comes to a boil, but to no more than about 3 to 4 ounces -- maybe as high as 6 -- and just simply sit there until all the radiation is nice and hot. Then you should see it start to rise again, probably rather quickly -- and that is when you want the boiler to cut out. If it doesn't do that -- rises to a higher pressure initially, or doesn't flatten out, then you need to put more venting on at the same location as that one lonely vent. You don't need it anywhere else. You might save a little fuel if you were to put a vapourstat on there in addition to the pressuretrol, and try setting at about 12 ounces as the cutout -- but I doubt that you'd save enough to pay for the control.

PMJ

@radcon,

Your system is perfect for natural vacuum. If you really want to improve your system's performance with respect to both comfort and efficiency, consider swapping that one vent with a simple and inexpensive check valve and just don't let all that air back in each cycle. Better yet put it on the return side of that rad in the garage - that's where mine is.

Simply put there are no positives to letting the air back in - only negatives. In even low vacuum the steam reaches the rads considerably faster on each new firing with no air to push out first; and the steam goes more to the rads in the coldest locations regardless of how the valves/orifices are set - automatically evening things out. You end up fiddling with valves a lot less and enjoying the results a lot more.

I admit I am still puzzled as to how it came to be that these systems were just allowed to turn into air processing machines, apparently simply because the fire went from continuous to intermittent.