Change to Front Draw-Off, When & Why

[DanielS.]

Hi folks,

I did a search and can see where this question has been asked before, but it doesn't seem to have been comprehensively answered (as far as I can tell):

When did evaporator manufactures go from rear syrup draw-off to front draw-off. I'm not talking about cross flow pans where you're drawing off from the section closer to the flue pan, but rather the syrup pan being behind the flue pan. I have a few D&G catalogs from various years from about 1910 to 1980. All the catalogs before about 1950 have the syrup pans at the back. This is how our older Champion evaporator before we got the new pan set.

I understand why the syrup pan would now be at the front - hotter fire, quicker control, &c. I'm wondering why they were ever at the back in the first place. There must have been a reason for it - just can't think what it was. Maybe this was back when more people were firing with longer slabs? I'd be very interested in your thoughts/opinions.

[maple flats]

I always reversed the flow as I could see that niter was building up. Hard to say in other terms, because so much variation in the time it takes for niter to build up on the bottom of the syrup pan. My best test on if niter was building up is that I used a nylon spatula and held the blade at about 45 degrees to the bottom of the pan with light downward pressure and pulled it towards me, If I felt it drag I used the amount of drag as my gauge. I also took into account how much more sap I had to boil, if almost done, I finished without reversing, if a lot left to boil, I reversed the flow. Just realize, the longer you wait to reverse, the harder the pan will clean at the end of the boil!
As I reversed, I also drew off about 2 qts of near syrup from the old draw off side and poured it into the new draw off side. For this I had a 2 qt SS pitcher which made it easy.
My evaporator had same side draw off, reversable, thus part of the time my draw off was in my 4th channel, next to the flue pan, the rest of the time my draw off was in the 1st channel, in front of the pan.

[DanielS.]

Thanks! But I still don't think I explained my question clearly. I'm not referring to cross flow or reverse flow syrup pans at the front of the evaporator - even if the draw off might in some cases be closer to the flue pan. Rather, I'm referring to the syrup pans being located behind the flue pan (closer to the stack) while the flue pan is located right at the front over the firebox. Back in the day all evaporators were like this; if you look at old equipment catalogs from about 70+ years ago you'll see this. At some point it must have become evident that it was better to put the syrup pans in front. I'm just wondering why that was, and why they were ever at the back in the first place.

[ecolbeck]

This is a great question and I have only speculation to offer. Aren’t there maple history professors out there? Maybe this is an opportunity for someone to get their PhD?

If the syrup pan was in the back where the fire was less intense it seems like sap would spend more time there giving the operator more leeway for determining when it had reached the syrup stage. This would make sense if syrup makers were using sheeting to determine if syrup was present because hydrometers were not in use or uncommon for whatever reason.

I know that on my pan I always have trouble each day getting a hydrometer reading and setting my thermometer because the temps are rising fast. Of course this is because the pan is small.

[BAP]

I would say sometime in the 70’s to 80’s range. When I grew up, we had an evaporator that was set up like you described with the finishing pans in the rear. It was from the early 60’s or earlier I believe.

[johnallin]

I would say sometime in the 70’s to 80’s range. When I grew up, we had an evaporator that was set up like you described with the finishing pans in the rear. It was from the early 60’s or earlier I believe.

My guess is more consistent heat at the back of the fire box and placing it in the rear it would be less affected by open door(s) when firing.

[Bucket Head]

I think John's "more consistent heat" is part of the reason. The other part being there were no RO's back when those rigs were prominent. So, the only way to get more water removed was to get more heat. Since most of the evaporation is done in the flue pan, it made sense to put it directly over the fire.

And it would have made brushing the underside of the flues a little easier, I'm thinking.

Steve

[Bucket Head]

I think John's "more consistent heat" is part of the reason. The other part being there were no RO's back when those rigs were prominent. So, the only way to get more water removed was to get more heat. Since most of the evaporation is done in the flue pan, it made sense to put it directly over the fire.

And it would have made brushing the underside of the flues a little easier, I'm thinking.

Steve

[DanielS.]

Thanks everyone for the responses! Yes, I suspect getting the sap pan over the firebox for the fastest boil was probably the main reason for it, and not killing the boil when you opened the door.

I guess my next question would be, why has it changed completely and universally? I can see the RO being a factor, where you're not having to get rid of as much water quite so fast. But there are still loads of people not running RO, and lots of evaporators being made for smaller operations without RO. I wonder why are evaporators like the D&G sportsman, most of the smaller Thors, etc., are made with the syrup pan up front? If we assume (probably an incorrect assumption) that rear syrup pans were best for non-RO operations back in 1950, why are they no longer ideal for non-RO operations in 2023?

All irrelevant questions, I realize. I'm not looking to swap mine around or anything. Just curious about the history & logic behind the switch.

[Bucket Head]

No, all good questions! They probably had draw off issues with those backward jobs. The back of your arch is the coldest- most of the heat has already been absorbed by the pans. Getting to syrup density might have been tough back there- and tougher yet with a lazy stoker! Syrup needs heat to finish and the whole pan system works on liquid density, which is greatly affected by the heat you put to it.

Steve

[The Heldeberg Sapper]

Now you've got me wanting to swap my back 2x3 flat pan with my front 2x2 syrup pan and see how things work. I just had the pans down for cleaning yesterday so ive missed my chance for now haha. Very slim chance that i will actually do it but now im super curious. I am not running an RO just good old firepower.

[Bucket Head]

Well, your rigs boil rate might respond to it. Seeing it's not a long evaporator and you wouldn't "lose" as much heat because it's a flat pan, it might be okay. If you had any size flue pan I would say forget about experimenting with it.

The first evaporator I had was a homemade 2.5 x 6 with two flat pans. The first 4.5 feet of pans boiled great. The last 1.5 boiled but not nearly as hard. Again, things are cooler at that end of the arch.

Steve

[BAP]

The evaporator with the syrup pan in the rear that we had was hard to get a good boil in the rear syrup pan. It was tough at times getting it up to temperature for drawing off syrup.