Vapor balancing? Dead Men question.

delcrossv

2 pipe vapor system with orifices /regulating-valves . NO traps on rads.

I'm assuming nearer rads would see steam first.

Am I correct that reducing the orifice size on faster heating rads would encourage steam to find rads further down the line?

Sort of "balancing back pressure " between emitters? Seems the only way without traps to provide positive close for filled rads.

Jamie Hall

Main and dry return venting!!! Then main insulating. Changing the inlet orifice or metering vavle size will indeed reduce the heat ouput of the radiator — but will not have much effect on how soon it sees steam. If the mains and dry returns are adequately vented, and the steam mains are insulated, even fairly long mains — say 100 feet or so — should see steam full length within 5 minutes of the boiler making steam, and in the context of a full burn cycle that's not that important.

delcrossv

@Jamie Hall , I imagine some thought was put into pipe sizing when these systems went in?

Seems none of this would have been an issue with coal, but is one with intermittent firing.

So in these modern times, you'd still be looking for longer cycle times?

Steamhead

@delcrossv , there were several systems that used this setup- ADSCO, Kriebel, Hutchison, Tudor- have you found any markings on the original rad valves?

Jamie Hall

Was thought put into pipe sizing? Much as we love the dead men… probably not always! But since the pressure drops, even with somewhat wonky sizing, are very low and the actual free steam velocity is remarkably high, I doubt that pipe sizing and pressure loss is as much of a factor as simply heating the pipes up — that insulation bit — combined with adequate venting. It's worth noting that the old boys didn't use crossover traps because it was easier (it's not) but because they recognized that they are essentially free flowing, in contrast with vents.

Cycle timing is one of the minor curses of on/off modern boilers. Ideally, even with modern boilers however, the optimum seems to be that the overall average firing rate matches the heat loss of the structure (obviously!) and that the "off" part of the cycle should be short enough that the system never really cools down. Doesn't work in the shoulder seasons. If one had a vacuum tight system (good luck with that) one could operate at sub-atmospheric pressures with some means of modulating the boiler output. Otherwise, one is really depending on the thermal inertia — heat capacity — of the radiation itself and the space to a lesser extent. I'm not sure there is a good way to minimize the problem of the more distant radiation not getting as much heat in warmer weather, though.

delcrossv

https://forum.heatinghelp.com/discussion/comment/1849379#Comment_1849379

No, unfortunately. Do you think they just throttled the hot rads down?

For my purposes, I'd better be careful with where the thermostat goes.

Steamhead

Vent the mains quickly, as @Jamie Hall said. This will level the playing field and you won't have to fiddle with the rad valves to balance it.

delcrossv

Vent dry returns fast too? Or does that not make as much difference?

Jamie Hall

https://forum.heatinghelp.com/discussion/comment/1849398#Comment_1849398

It makes even more difference… and if the system uses crossover traps, as many vapour systems do, the dry returns are your ONLY vents.

mattmia2

Because it is 2 pipe and the seam and condensate don't have to share the same pipe, the mains can be much smaller so they heat faster than 1 pipe mains.

delcrossv

https://forum.heatinghelp.com/discussion/comment/1849410#Comment_1849410

No crossovers, everything is dripped.

Jamie Hall

https://forum.heatinghelp.com/discussion/comment/1849534#Comment_1849534

Even so — the dry returns have to be vented. Copiously. And with no crossovers, so do the mains.

delcrossv

Gotcha.

mattmia2

A lot of vapor systems have some sort of device at the boiler that is a crossover trap but doesn't look like one.

Jamie Hall

https://forum.heatinghelp.com/discussion/comment/1849560#Comment_1849560

All kinds of strange stuff, indeed. But I was specifically referring the crossovers from the ends of the steam mains to the corresponding ends of the dry returns.

mattmia2

Others i think vent the mains through the emitters and the dry returns which probably works ok because the mains are much smaller than in 1 pipe systems.

Jamie Hall

I suspect it does work OK — but there's something to be said for a nice big crossover or vent…

On the other hand, maybe not. Consider that Cedric's entire system is vented through one Gorton #2…1300 square feet EDR… and works just fine at 2 ounces gauge or thereabouts.

Hmmm…

delcrossv

https://forum.heatinghelp.com/discussion/comment/1849593#Comment_1849593

Maybe because it doesn't matter if the dry returns are full of air, the volume you need to vent is just the mains, risers and rads. Dry returns shouldn't have steam in them anyway. (?)

jumper

If dry return is mechanically evacuated before firing; AND there are no traps….. then steam fills all radiators quickly. IF boiler size is sufficient. At least I think that was the theory or hope behind the design of some steam systems I remember. Situation became interesting when boiler was replaced with multiple small ones. Operator would cook occupants early AM then shut down all but one or two. Procedure repeated late afternoons. Can't do that with HHW.