mooseman100 wrote:I am nearly complete installing my efm 520, getting pretty excited.
You can continue getting excited. You have one of the finest stoker boilers made, and it normally
doesn't require a dump zone. You can add an aquastat for that purpose if you wish, but I have never had an issue with high temperatures with my 520 (my dad doesn't either). An EFM 520 boiler holds about 40 gallons of water (Highboy is about 54), and weighs 750-800 lbs. That is a lot of mass, and as long as you have the controls set properly, it should maintain a stable temperature just fine. One of the nice features of the EFM stoker is that it doesn't require 15 minute timer cycles to keep the fire alive. 1-2 minutes of run time every half hour is usually sufficient; especially if you have a strong chimney.
When set at 5 teeth of feed, my 520 will only "coast" about 10 degrees after a heat call...less if the stoker was only running for 10-15 minutes. When set at 160/200 and 1minute every half hour on the timer it usually hangs out at 160-170 degrees.
kstills wrote:However, you're boiler probably came with a high limit 'dump zone' aquastat, and it's much much better to be safe and have it set then it is to have your boiler overheat at some point down the road.
You can order a brand new DF520, and it won't come with a separate aquastat for a dump zone. The high limit function of the triple aquastat will prevent the stoker from running above that setting. If someone is concerned about the aquastat malfunctioning, it is easy enough to add a second control to disable the stoker above a preset temperature. I had an extra L4006A kicking around, so it is installed on my 520 and set at 220 degrees. 10 tons later it has never approached that temperature.