Pre-heater question

[Bucket Head]

Hi Guy's,

This question goes out to all the 2x6 or 2.5x6 evaporator owner's.

What size copper pipe, and how many feet of it, does your pre-heater have?

I am going to build one for mine and I am trying to find out what other's have so I have something to go by.

Thank's,
Steve

[Fred Henderson]

I used 1 1/4" for the headers and 3/4" fin tubing for my laterals. Get as much in as you can, 20 feet would be a good place to start.

[maple flats]

When I had a 2x6 it had a 2x3 flue pan. I made a double decker pre-heater with all 3/4" copper. Each level had 5 passes and the whole thing mounted with a tilt to it. The inlet was lowest and the outlet was high on the opposite corner and then dropped into the float box. each pass seemed to have about equal condensation on it so I think each pass worked about equally. It was set up so that the inlet immediately went thru a tee for the next higher level. The lower level had 5 parallel rows and then fed upward to theupper level just before the outlet. The upper level as I said started just after the 1st level inlet, teed up to level 2 and then had 5 rows like the first, and at the outlet the lower level teed into it. This way the pre-heater was good to go with either end as inlet, or in other words it was simetrical (spelling?). This worked very well and was entirely under the hood because my 2x6 had the float box above the flues pan and on center side to side but at one end.

[maplekid]

does the vaporlock issue come into play when constructing a prehaeter should there be a vent of some sort?

[Bucket Head]

Maplekid,

I'm going to start trouble with this reply, but here it goes.

I look at vaporlock's and Bigfoot storie's like this; people say they have seen them, but I've seen no evidence of them. Their going to have to prove it to me.

I don't know what to say about vented system's other than if that's what someone has and it's working, keep using it. Don't fix something if it's not broken.

As for vapor lock, I do not know of anyone who has had one. Gravity is a beautiful thing. It work's 24/7, without fail. I know of several gravity feed, unvented system's that perform flawlessly. I have spent hour's next to these rig's and they never had a problem.

As long as your preheater outlet is lower than the inlet, and the feed tank is higher than the preheater inlet, it will flow without a problem. The opening in your feed tank is your vent. Just like the hole in the gas cap on your lawn mower, ATV, sap pump, etc. Another benefit to the gravity system is that it drain's out by itself and will not freeze.

Now that I am done hi-jacking my own thread, I would like to get back to my original question: How many feet of tubing is in a pre-heater on a 2.5x6 evaporator with a four foot flue pan?

Steve

[802maple]

Not to be sarcastic but you haven't seen one get hot enough then. Most of the new paralel preheaters today don't get hot enough to vaporlock, but my old Grimm style preheater that went from 1 1/2 to 3 1/2 copper and went in a continous loop of about 25 feet back and forth would boil sap in the preheater. I don't understand why Grimm stopped making them as they would really heat up the sap and yes they would vapor lock and maybe that was the reason. The newer style preheaters that have a multiple pipes don't warm the sap as well because the sap isn't moving in all the pipes, sap like water will find the easiest path of resistance and that is usually the first 2 or 3 pipes and the others stay stagnant and don't move is what I have found

[Bucket Head]

802Maple,

How hot is "hot enough"? How hot was the incoming sap from the heater you spoke of? Did you ever get a thermometer in the sap to verify how hot it was?

If your preheater was level, or had an uphill tilt to it toward's the outlet, you probably had air trapped in it before you ever put fire to the pan's.

When built correctly, the gravity feed style I described can not trap air in it. When you open the feed valve, with the float valve open (down), the sap pushes all air out at the float valve.

Steve

[Parker]

On my Grimm preheater the sap goes in the bottom and out the top,,it has one continious 2 1/2? length of copper pipe passing back and forth inside the steam chamber,the chamber in about 6 feet long,there is a drain on the bottom loop and a vent on the top loop,,If I close my steam stack off while boiling the preheater can vaoprlock,,will DEFINATLY start "burping" or blowing bubbels out the vent pipe (with a hard boil going) . up to you,,BUT,,even with the vent pipe and the steam stac open a few time last year I noticed my flue pan getting lower and lower,,went to the float box,,nothing comming in!!600 gallons in the overhead feed tank,,have been boilg for hours,,held the float all the way down and and bunch of steam-real hot sap comes burping out,,,,,,you got to keep a constant eye on them,,,, I am going to put a regular damper in the steampipe this year to try to hold the steam by the pipes a littel longer,,,,running with the stack closed is too nervewracking for me,,too much to wacth,,,so this last season I ran with the stack fully opend,,,
But,,I have never seen Bigfoot,,,have caught a glimps of some "hidebehinds" though

[802maple]

Buckethead

With a thermometer in the float box the sap would be coming most of the time at around boiling point, As Parker said , you have to constantly keep watching it. or you could be out of sap. The sap most of the time would come out at 210 - 212 and when it is boiling in the preheater it will create gas. I had bleeders that I would make sure all the air would be out before I started. I agree that the newer style of preheater is not so prone to air locking but they don't warm sap like the older grimm style.

[ziggy]

Bigfoot may exist, but I don't know. Vapor lock that does exist, I have seen it first hand. 2 things for a pre-heater to work properly the input must be lower than the output, heat rises, and you need enough piping to transfer the steam heat to the sap. which if built properly even a 2 x 6 will give you sap coming out of the pre-heater a tempature of about 212- 214 degrees, getting higher than that is very cost inhibitive. If I were making a pre-heater for a 2 x 6 again I would use 1 1/2 headers with 6 runs of 1/2 thin wall copper pipe. I would place the inlet and outlet at the same end of the evaporator; near the stack; and use a parallel flow. more length of small diameter pipe will transfer the heat faster than larger diameter pipe.

[Sugarmaker]

Well I havent seen Bigfoot ethier but after boiling for 6 years with a home built parallel flow preheater designed after the Leader style I can tell you that it will trap hot air and stop the flow of sap into the rear pan. I have a 1-1/4 dia manifold at each end and 10, 3/4 inch thin wall copper pipes running up hill from the back of the pan to the front then a return line runs back to the lower end and into the float box. I did install a Taylor thermometer in the exit line above the float box and it usually runs at 200 deg, F when firing is continuous. I do have this system vented at the upper manifold in three places, center and both ends. All vents are allowed to overflow back into the flue pan. This past year I did not have any problems with air trap. Prior to the season starting I carefully leveled the upper manifold and this seemed to minimise the air trap concerns. (I know you are looking for exact information on a 2 x 6 vs the 3 x 10 we have.) My recommendation is, add the vents and you can close them off if you want to try with out them. Seems to make sense that as yo approach the boiling point you will have the potential for air lock. If the sap flow never allows you to get there then it may not be a problem. I think the goal is to get the sap as hot as possible entering the flue pan.

Good luck with your preheater. Add some features to remove the gallons of condensate that will be produced.
Two of the vents are the kind that straddle a copper pipe for installing a waterline for a ice maker. Then I attached a small dia hose.

Regards,
Chris

[Bucket Head]

802maple, Ziggy,

Obviously, I am no expert when it comes to preheaters. That's why I asked my original question, and why I'm going to ask these next question's.

Why does the inlet need be lower than the outlet on your preheater's making the vent a necessity? Heat will transfer no matter how the pipes are oriented. Just like automobile radiator's. Some have tubes vertically, and some are horizontal.

The potential for hot sap to be "released" is enough for me to shy away from that design.

Why do you need to heat the sap to near, or at the boiling point? That right there seem's to be a pretty tight rope to try and walk. What's wrong with 205 or 208 degree's? 200 degree's is certainly better than the 40 degree's your outside tank is, right? One of the rig's I spoke of has a sap temp. of 205 all the time, never lock's up, and never "backfire's" sap at anyone.

200 degree's or so seem's like a good temp. to try and acheive while eliminating the potential for boiling in the preheater.

Steve

[802maple]

You are right in asking why do you need to preheat sap to boiling point, you don't is the answer.

But if you are heating your sap to that 200 degree level say instead of 212 everything will work fine in a preheater that continously go down hill to your evaporator. If for some strange reason your sap heats up to 212 and boils in your preheater (as we all know if you hang around this business long enough strange stuff will happen) I guarantee that type of preheater will vapor lock.The only reason that the manufactured systems head up hill is just in case it gets hot enough for that to occurr is so that the gases will go to the highest point and out the vent.

Now after having said all this I am going to confuse the whole subject by saying unless you have to have hot water from the the preheater instead of from conventional means that preheaters aren't worth a grain of salt. I have had plenty of evaporators both with and without preheaters or preheaters added at a later point and I have never noticed the 15% if any increase in the evaporation of the sap. The only good point in my opinion is that you have a endless supply of hot water from the condensation that comes off from it. I will probably say that a small evaporator might show some increase but they are the only ones.

[Parker]

I was told that the steam hood (holding the steam aginst the sap in the flue pan) slows down the boil-but the pre heater increase in temprature make up for this-so you dont lose any thing-but you do gain hot water

[802maple]

What you say could be true Parker, I don't know as I not a physic's major all I know is what I have personally experienced.

[brookledge]

What usually happens is that every thing can be going smoothly, you can have your hood damper just right so that your sap coming out of the pre heater is around 200-205 or so and then all of a sudden the float closes down because the foam starts to rise or for what ever other reason and now the float is not allowing any sap movement, the temp starts to climb until gasses are released in the sap and that needs to go somewhere.
Remember that for every 1 psi in your steam hood the temp increases 3 degrees. So if you damper down your hood and have 2 psi it means the steam temp is around 218 so if your sap is not moving in your preheater it will definately cause the sap to boil inside the tubing.
It doesn't take much to raise the pressure 1 or 2 psi.
I know that in my case when I close down my damper the entire hood starts to dance, rumble and bulge. It would be interesting to see just how much pressure I'm getting without blowing the hood up.
Keith

[RileySugarbush]

For a reality check, if you had a 2x4 foot steam hood, it would need to weigh over 1000 lbs to get 1 psi. Unless you are bolting the steam hood down, I doubt any of us will raise the pressure anywhere near 1psi.

[Pete33Vt]

I am going by my own experiance here. On my 40x12 last year was the first year its ever had a preheater on it. And I saw a noticeable differance in gallons per hour with it than with out it. And i was only getting an average of 160 degrees at the float box in the rear. Plus I had the hot water. In my oppion the water coming off the preheater is that much lesss I have to boil out in the front pan. And this by no means is a factory preheater. There were other factors involved also, such as different fire techniues, and a better forced draft system. But I wouldn't be without my preheater.

[802maple]

Pete
I would bet that your extra production was mostly from your better firing and forced draft and not your preheater, as my experience has been from oil fired and unless somebody put some go juice in my oil nothing changed, but who knows.

[ziggy]

Any pre heater I have ever run has aways given me 10 -12% increase, remember you do need a drip tray under the pre-heater to catch the condensate dipping off. I have had one on a 2 x 6 wood fired, a 2 x 8 wood fired and a 3 x 10 oil fired. And the hot water is great.

[Maplepro]

We ran a Pre-heater on our 5X12 that we had years ago the only advantage i found was the hot water we seen no increase in production i would have to agree with 802 that the increase that Pete got was from better firing i would have to say if you are looking for increased production and u don't have a forced air i would look at that before I would put a pre-heater in.