How to stop finish pan flooding

[BCPP]

Looking for thoughts / ideas for my somewhat unusual operation. We have a LaPierre minipro that we use mainly for demonstration purposes during our maple festival. Unfortunately this means that a lot of the time I'm firing up the unit at 9am and then stop firing at around 2pm so that the fire can die down and we can close festival at 3pm. The box retains a lot of heat and I typically evaporate another 5gal of sap overnight as it cools off. During this time I leave raw sap supply valve as well as the valve between the evap and finishing pans open.

The problem I have is that occasionally the float valve for the finishing pan sticks open. Then, when I arrive the next morning I'm greeted with a finishing pan that has 6" of sap in it! Most of the time it appears the float is getting held open by tiny pieces of debris (not sure what it is, maybe flaked off bits of nitre). Its only held open a really small amount but of course, over a 15 hr period a lot of sap can leak through! Happened again last night. This time I think it was the sap freezing in the float tube that forced the valve open. Luckily it quickly froze the entire tube so only increased the finishing pan depth by about an inch.

I'm concerned that if I were to close the ball valve that feeds the finishing pan the latent heat might be enough to evaporate the pan dry. Is that a valid fear? Do I flood the finishing pan with an extra 1/2" and then close it? That way I have a minor flooded pan 100% each morning or take my chances and have a major flood 10% of the time! Any other thoughts or ideas on what to do?

[wnybassman]

I have a similar evaporator and I have to close the valve for the same reason. I flood the pan an extra 1/2" or maybe a full inch. By the time I shut down everything else in the shack the boil in the front pan is nearly non-existent, and at that time I feel safe walking away from it. I have never come back to it shallower than I am comfortable with. I do burn straight pine the last 20-30 minutes when winding down so I don't have a lot of (or any for that matter) coals left over too.

[Mark-NH]

Flood the pans. You can calculate roughly how much you need to flood. I know it can be dissapointing to undo some of your gains by sending sap into your finish pan but it protects against burning the pan while controlling how much material makes it past the float. Biggest bonus in the piece of mind it gives you when you lay your head on the pillow.

[Big_Eddy]

I stop firing 30 mins before I plan to leave then, as I am leaving I close the tank valve, remove the feed hose and drain it, add a 5 gal pail of sap to the first channel and finally close the valve between the flue and syrup pans.

Removing and draining the feed hose can save me an hour thawing it out the next morning if it's cold out.

[Sugarmaker]

Good to hear from Big Eddy, my hero!
Yes better to have little too much sap than the alternative!
You can drain some off in the morning and add back in. You haven't lost anything. Its is still sweeter than it was!
Regards,
Chris

[Russell Lampron]

I fill my front pan to about an inch higher than I normally run it and close the valve to the pan. After it cools it's close to the level that I normally run at or a little lower. I've never had the pan boil dry or even close to it.

[maple flats]

I do about the same as Russ. I dump the head tank about 5 minutes after my last fueling of the day, into my back pan (when I have about 18-20 gal of concentrate in the tank). Then I drain the pre-heater into the back pan. I then do my clean up for shut down. My evaporator takes about 45-50 minutes before the front pan boil slows almost to a stop and the bed of coals are almost all burned up. I then bring the syrup pan level up from about 1" up to 2" deep. I then close the valves between the pans(raised flue so I have 2 valves closed) Then I put my covers on every opening (I made a SS cover for each float box (3) and for the syrup pan. The back pan has a closed hood. Then I shut off the lights and go home. In the morning, when I return I usually have about 3/4-1" in the front pan and the back pan is about at normal operating level (about 1/2-3/4" over the raised flues.
I never had any issue doing that, except occasionally I forget to close the valves between the front and back pan after the first boil of the season. When that happens, the front pan is at about 4-5" deep the next day. Even with that, I just light the fire and let it evaporate. In about 60-90 minutes it is down to my 1" operating level and when ready my first draw is longer than normal (auto draw). That happens once every 3-4 years, this year it did.