The controller , the SA-12 is a micro PLC, made by Crouzet, an older model, the newer model retails for about $150 or so. I run a program that I wrote, which controls my stoker in a manner similar to the way the Coal Trol does for coal stoves. The grey box on top of the boiler converts the water temp to an analog voltage which the PLC reads.How much did the contoller SA-12 cost ?
Changing the blower speed doesn't have much affect on draft when its read at the breech of the boiler, it has more of an effect when you monitor the overfire draft, buts its still not that great a change, maybe .01" or so. The combustion blower on the Harman just isn't that big, I suspect its somewhere in the 75 to 100 cfm range.Can you still keep your -.05 draft with the blower running full speed?
When the boiler is cooking, the draft is around .05" or so, in idle its more like .01 to .02", especially in the summer with the warm weather.
What I have noticed with the restrictor plate, which I did have installed for a while is that it tends to limit how much heat you can get out of the boiler when its firing close to capacity. Harman's method to check the draft is detailed in the Magnum stoker stove manual, your supposed to monitor the draft at the breech, and then monitror it over the fire, by removing the small 1/4" plug and inserting the probe there. There is a plug in the door of the boiler also for this purpose. They don't mention at what firing rate your suupposed to do this.
Harman also assumes that the combustion blower only runs during the actual stoking, not continuously as many people on this forum do. Without the blower my boiler will go out within 15 minutes or so in the warm weather, there just isn't enough draft to keep it going especially with the low idle fire I run. With the blower, I have never experienced an outfire. By running the blower at a lower rate, I can keep more of the heat in the boiler, and I think I get a better burn with less unburned coal in the ash.
Keystoker has added a small blower to help with outfires in the warm weather, and If I remember correctly, they claim it saves coal also.