Divided pan questions

[NHnewbie]

I bought a barrel evaporator off craigslist a few years ago, and until this year, I have essentially been batch boiling with it. I have a few times had enough sap to create a gradient, but I almost always finish my batch the same boil.

My question is, now that I have a sugar house and I can leave the evaporator, if I shut down the boil and not empty the pan into a pot to finish on a propane burner, how long can I leave the pan before returning to boil again? IE does it have to be overnight then start again, or can I boil say on a tuesday for a few hours, shut it down, then pick back up on a thursday?

[BCPP]

In normal years (not this year!) we are running in part to support our maple festival so we often shut down for a few days so that we can boil on weekends. A lot depends on ambient temp. If it gets warm I'd be reluctant to leave for more than a day or two for fear sap in evap pan would start to grow. But if it's cold then 3-4 days should not be an issue.
Two problems we've had:
1)Input float valve freezes solid - can be a bit hairy on restart as it's a race between evap pan losing too much and the heat transferring to the float valve to let more sap in!
2)more of an annoyance than anything but on three occasions once we've shut down we've returned a day or two later to find that the finishing pan float valve has stuck open on finishing pan is flooded so have to boil for 4 or 5 hours to get gradient back! Appears a tiny bit of nitre swirls up and gets on the valve seat, holding ever so slightly open.

[NHnewbie]

Thanks, that's along the lines of what I was guessing. I'm hoping that this season the ambient temps stay seasonable (30s-40s) during the day. Last year was rough, we had a few days in the mid 50s and my last day boiling it was 70. It felt like a summer evening as I had to sit far away from the evaporator so I didn't bake.

[Openwater]

I've got some similar questions about divided pans. I'm currently a steam-panner, but would like to get a divided pan to put on my evaporator which has a top opening of 12" x 48" which I'd assume is enough space for 3 channels, 48" each. I'm just not sure if I'm currently producing enough sap to get the pan sweetened and keep it sweet, or if I should just continue batch boiling in the steam pans. Since this will likely be a custom fabricated pan, I wouldn't mind getting some suggestions regarding design.

[DrTimPerkins]

Two problems we've had:
1)Input float valve freezes solid - can be a bit hairy on restart as it's a race between evap pan losing too much and the heat transferring to the float valve to let more sap in!
2)more of an annoyance than anything but on three occasions once we've shut down we've returned a day or two later to find that the finishing pan float valve has stuck open on finishing pan is flooded so have to boil for 4 or 5 hours to get gradient back! Appears a tiny bit of nitre swirls up and gets on the valve seat, holding ever so slightly open.

A float valve is not always a reliable method of shutting down the feed line. Many float valves will pass a little liquid even when shut off. A positive shut-off valve between the feed tank and the float valve is a good idea. This will help with both these issues and also can be shut off if you need to do major adjustments on the float valve itself.

[BCPP]

I do have a ball valve shut off but I've always been concerned about boiling the finishing pan dry. When I shut the evap down I wait until fire goes to coals that are below the grate. We usually have about 5 gal of sap evaporate over night from the latent he as t in the firebox. While I suspect most of this is in the evaporating pan I've been too chicken to shut off the feed to the finishing pan in case it isn't!!

[maple flats]

I've always shut off my feed line. I actually have a freeze proof valve on the head tank (a ball valve with a rubber of some type ball so it can freeze without bursting the valve). like this: https://www.brewershardware.com/TC15VBFVPT.html?category_id=274 Before I do that if I have sap (actually concentrate) left in the head tank, in fact I have a site level on my feed tank and it's marked when to stop firing so I have the concentrate to add to the pans, I raise the level about 1". That allows for evaporation from heat in the bricks. I have both a cold sap and a hot sap float box, the valve between the back and front pans is also closed after I raise the syrup pan level from 1" o 2", because that valve for hot sap has a slight leak, which could totally fill the syrup pan if left open.
The valves I linked are 1.5", I believe they have larger and smaller sizes too.