Extra part for vf3000
This is a 2008 post from member "Highlander" from the above thread. "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."
My wife says I only half listen to her. She may be right cause for sure I only half read Highlanders post in 2008. Some of you who have been around on the forum for many years may remember the story of the first time I fired up the VF3000. It filled the basement with flue gases. The Harman manual at the time had no mention or even a picture of the restrictor plate for the combustion fan. It was an extra part with no explanation. By running the fan unrestricted it blew more air into the combustion chamber than could be exhausted with the draft I had so the flue gases backed out of the hopper. Harman was neither helpful or apologetic. Later versions of the manual the restrictor plate magically appeared.
Anyway once I figured out what it was and where it went (this was in 2003 before I had found the coal forum) I installed it and adjusted it by checking the draft through the hole in the combustion chamber door. Problem solved. Then last heating season following Highlanders lead, I installed the motor speed control on the combustion fan. For those of you not familiar with the VF3000, the combustion fan is only intended to run while the stoker is operating. This control allows the fan to run when not stoking but at a lower speed. It made a big improvement in the overall performance of the system. In my case it improved the draft of my chimney which is an 8x8x17' terra cotta on the exterior of the house by keeping it warmer. I never changed the restrictor plate setting after this modification. The boiler worked better than before and all was well. That is until Wednesday morning when it was 9 degrees.
So yesterday I went over the boiler top to bottom trying to see if there was a problem that maybe I had missed. Started messing with the restrictor plate position and eventually just opened it up fully. I fully expected to get flue gases out of the hopper but I did not. The improvement in the chimney draft from the fan speed control modification was enough to overcome the fan. Naturally the fire is much more vigorous as a result. This morning the boiler temp was 180 degrees. It was not quite as cold this morning as yesterday but I think this is making a big difference. The real test will be Friday night into Saturday morning as it is supposed to be single digit temps again. Once the weather goes back to a more normal temp, i may have to revisit the restrictor plate setting. But for now this thing is working much better. I did notice my stack temperature is about 25 degrees hotter than before. Right around 300 degrees north of the baro.