Raised and Drop

[Sugar Sue]

Could someone tell me the difference between raised and drop flues. Does this refer to the arch or the pans?

[maplekid]

your evaporator does it have these channels in the pan that drop down in to the pan. if it does the it is a dropflue. the opposite is a raised flue

[danno]

Or ... when your sap (flue) pan is sitting on your arch, are your flues above the top rails of the arch (raised) or do the flues sit lower than the top rails of the arch (drop).

[Sugarmaker]

Sue,
Danno answered it well, to add a little. The arch is a factor too. I think you have a dropped flue system ( The flues extend below the rails of the arch.). A raised flue arch is designed more shallow in the back and has a hump to direct the heat up in to the raised flues of that type of pan.

Chris

[RileySugarbush]

Here is a dropped flue, viewed with the syrup pan removed. The flues are open to the pan above and when filled with sap provide lots of additional area for heat exchange. In a raised flue, the slots you see are inverted up into the pan and hot exhaust gasses flow up into them. In that case, the arch floor needs to be up close to the bottom of the pan to force the gasses up into the flues.

[bobsklarz]

Thanks for asking the Ques. Sugar Sue. I was wonderin the same thing. Now I wanna know is one better than the other? And, Do ya have to remove the whole pan and empty it (drop flu) when you're done boiling?? If your shack freezes and there's sap in those flus,....problem?? Thanks for your time and your answers! bob

[hard maple]

Just buy a new MAX theres no difference
There the same thing

[Thompson's Tree Farm]

If you are a drop flue person, drop is better, if a raised flue person, raised is better.
Freezing in the flues is not usually a problem. As the sap freezes, the top freezes first. The water freezes first and the remaining sap has a higher and higher concentration of sugar thus lowering the freezing point. For an extended cold snap, put an electric light bulb under the pan or start a small kindling fire under the pan once a day for about 5 minutes.

[Flat47]

SS,
One thing to watch for when firing a drop flue, wood-fired rig is hitting the flues with the wood. I've seen several used flue pans dented and leaky from being hit.

[Four Saps]

Is there any advantage or disadvantage to drop or raised flues?

Four Saps

[3rdgen.maple]

Four Saps I feel it is a preference thing. I think some drop flues don't have drains in them which makes cleanups hard, lifting a heavy flue pan off an evaporator is a pain. I had a drain installed on mine when it was made and I am very happy with it. Went with the drop cause I could only raise my holding tank so far and I could not get it high enough for a raised. There is only one float box on a drop flue to keep sap regulated in the pans Which is just fine for me less things to go wrong. A raised flue has two float boxes one to regulate sap in the flue pan and one to regulate sap in the syrup pan.
Same size flue pan raised or drop has the same evaporation rate if they are setup right I was told. As far as wood hitting the drop flue when bricking the arch cut slots in the brick just in front of the flues and put a peice of angle iron in front of them problem solved. Works very well for me.

[mapleman3]

Thats when you get a brandy new mid sized shop vac and dedicate it to the pans for sucking it out... or a good pump!