As a result of its recent failure to generate more than a minimum amount of heat for longer than a short period, I am in the process of cleaning-up and upgrading the single pipe steam radiator heating system (old American Standard gas boiler) in my elderly mother's 1920's two story single family home in the San Francisco area (yes, there is some steam out here!).
The system has 11 cast iron radiators (4 downstairs and 7 upstairs, two of which, in upstairs bathrooms, are smaller than the rest). (I have not yet calculated the EDR of the system, but the 9 larger radiators are 9 two-column fin ones such as that pictured in the One Pipe Steam section of Dan's A Steam Heating Primer posting in this site.)
I know that there are, or have been, a number of issues with the system, but I am addressing what I can more easily do now to get things going in the right direction. Other things, about which I may post inquires down the road, such as addressing near boiler piping and venting issues, will have to wait.
Among other things, I have so far (i) cleaned out (simmering in white vinegar) or replaced all the Hoffman air vents on the individual radiators, some adjustable, but most fixed, so they all vent well in and out; (ii) replaced the old, almost completely clogged McDonnell-Miller 47-2 (so the proper water level is now being maintained and the low water cut-off switch isn't opened and doesn't then take hours to close); and (iii) replaced the completely clogged pigtail on which the Honeywell Pressuretrol sat (so the Pressuretrol doesn't cut out and then take hours to cut back in).
Things are working much better now, though the above work has just been completed and I have not been able to do a careful watching of the entire system on an extended basis. Nonetheless, all the radiators vent air and, sooner or later, get fully hot, and the boiler cycles in a constant, though--because of the pressure gauge issue that I address next--unknown pressure range until the thermostat stops calling for heat (the Pressuretrol is set for .5 psi cut in and 1.5 psi cut out, though its accuracy is not known).
Thus, as a further upgrade, I'm next replacing the existing 0 - 30 psi pressure gauge (with vacuum range as well), which, when the boiler is stone cold, sits at about 1.5 or 2 psi, with a new one, and also getting a low range--0 - 5 psi--pressure gauge so I can better "dial in" a lower operating pressure for the system.
Finally (and the basis for this post), I am going to get a Honeywell VaporStat L408J controller to serve as the fine cut in/cut out controller, and then repurpose (as suggested on this site) the Pressuretrol to be the fail safe (though not manual reset) high pressure (say 4 or 5 psi) back-up cut-out (on a separate pigtail, of course).
But which VaporStat range should I get, the 0 - 4 psi one (the 1017) or the 0 - 16 oz/in2 (the 1009)?
Since I don't yet know if the optimal pressure range to run my mother's steam system is, say, .5 - 1.5 psi (the low end--assuming accuracy--of the Pressuretrol), or lower, say 4 oz - 14 oz, I'm torn about which VaporStat to get since the split between them is right in the middle of what the likely optimal cut-out range would be.
Any thoughts from the those here who have vastly more experience with and insight into steam systems and their controls than I (though I have learned a huge amount from reading here and listening to Dan's videos, etc., since my mother's furnace went South just before Christmas) which is the optimal one to get?
Thank you all. Nick