Preheater fab

[bmbmkr]

I have every thing cut and clamped up, nothin soldered yet. I wanted to run this past you guys. Take a look at my pics, and let me know if my vent is in the right place, it will be taller than the head tank, also the whole heater is angled 45 from left to right, and will also be angled 5 or 10 deg from rear to front for thermo siphoning. any advice comments, appreciated

BMB

1527415275

[psparr]

Don't really need the 45 degree angle. As long as the outlet is higher than the inlet. Would be a nice experiment though.
Looks good though.

[bmbmkr]

I angled it so it would fit in my steam hood,I figured the more surface area the better

[psparr]

Sounds like a plan.
Sure beats my lack of a preheater.

[optionguru]

Will you be able to remove it easily when you run out of sap? you can have an issue with the sap turning to sugar in the pipes if you run out and keep it in the heat.

[Maplebrook]

That looks good. I used a similar one that I made myself. It would heat the sap to 180.

Comment on the vent: Instead of plumbing a vent pipe higher than the tank, I put a ball valve on the vent pipe where it exited the hood, connected a piece of 5/16" to the valve and ran it to the float box. This saved heating the sap in the vent pipe and it kept the system "closed" so the head tank pressure would keep the sap pushing against the float.

Comment on the pipe size: Looks like all 3/4" copper. I used 3/4" for the manifold and 5 runs of 1/2" for the heater pipes. Smaller pipes gives better heat transfer. (voice of experience there!)

Good luck!

[bmbmkr]

Will you be able to remove it easily when you run out of sap? you can have an issue with the sap turning to sugar in the pipes if you run out and keep it in the heat.

My plan is to isolate the preheater with valving so that I can take it out of the loop yet keep sap going to the float valve, I would have never thought of sugar in the heater, good advice, thanks!

[bmbmkr]

That looks good. I used a similar one that I made myself. It would heat the sap to 180.

Comment on the vent: Instead of plumbing a vent pipe higher than the tank, I put a ball valve on the vent pipe where it exited the hood, connected a piece of 5/16" to the valve and ran it to the float box. This saved heating the sap in the vent pipe and it kept the system "closed" so the head tank pressure would keep the sap pushing against the float.

Comment on the pipe size: Looks like all 3/4" copper. I used 3/4" for the manifold and 5 runs of 1/2" for the heater pipes. Smaller pipes gives better heat transfer. (voice of experience there!)

Good luck!

Dang it! I thought more copper would mean more heat, but then you are right, there is a lot more sap volume in 3/4".....pondering another trip to the plumbing supply store now..

I was wondering about insulating the vent. If your system is closed, doesn't that negate the vent all together? I thought the purpose of the vent was to allow any inadvertent steam to escape, and prevent the pre-heater pipes from bursting catastrophically?

[wiam]

On both rigs I have had preheaters on they vent air out quite often. I run a hose way into the rafters. I would not chance a valve in this line. I doubt there would be a sugar problem in a preheater in a steam hood. The rig should be cooling down when you run out of sap.

[johnallin]

I ran my vent tube with 5/16" milk hose, straight up and back into the head tank. When she "blows" it's like a whale spouting - I didn't want to take a shower in hot sap.

[Aa2tn]

I also run a small tube up to a height above the sap tank. I have 7 2" diameter tubes in my preheater and it works just fine. There may be more volume of sap per square inch of surface area (not sure, I never figured it out) but the sap volume flowing through the tubing will be at a slower pace, so it will spend more time in the preheater and still reach the temperature.

[johnallin]

Keep in mind that the sap only moves as fast as your evaporation rate, which is a trickle at best on most rigs. It's in those tubes for a long time.

[maple flats]

I have vents on my preheater in 4 places, but I've never had to bleed the system. My head tank bottom is a little more than a foot above the outlet (high end) of the preheater. I still think vents are a must. When I run out of sap, my preheater gets drained but never removed.

[bmbmkr]

Thank you all for the advice. I truly appreciate all of your time and insight.

[bmbmkr]

Gutters...do you all have gutters under your pre heaters to prevent condensation from dripping back into the pan? I thought about making some from flashing. Any input?

[wiam]

There would be almost no gain in efficiency if the condensation was not removed. But efficiency is not why I have a preheater. It is for a source of hot water

[mellondome]

But you don't get hot water if you don't have a catch pan for the preheater.

[bmbmkr]

I understand the need for catch pan/gutters, how are yours made? a tray? gutters? pans? I'm not near any other sugarers, and haven't seen one in person, I'm going off what few I have seen on here and my imagination.

[wiam]

Most manufactured preheaters have a tray with drain outside hood. I have seen it don with individual channels under each pipe.

[swampyankee]

Hello

Perhaps a stupid question but I will ask....why wouldn't a couple of small pipes (SS sched 80) across the exhaust gas flowpath pick up more heat (possibly too much) and be a simpler/cheaper solution? Kind of like a feedwater economizer on a large utility boiler

[wiam]

Hello

Perhaps a stupid question but I will ask....why wouldn't a couple of small pipes (SS sched 80) across the exhaust gas flowpath pick up more heat (possibly too much) and be a simpler/cheaper solution? Kind of like a feedwater economizer on a large utility boiler

There are stories of burning sap in pipes near the flue "stack". Also the preheater intue steam hood will give you a supply of hot water. Which is not usually available in a sugarhouse.

[johnallin]

Here's a picture of the pre-heater I put in last year. It's made by Leader. Note the drip tray. Good luck with your project. John

15286

[Bucket Head]

Remember, warm sap turns into bad sap and bad sap gets nasty. I always flush my preheater out with water after shut down. I rinse my head tank out and then I put some water in it to flush out the preheater, letting this water drain out into a pail to dump. Your rig and the sap in it stays warm for some after shutdown and that allows sap to "stew" in the pipes if it's left in there.

[Aa2tn]

Keep in mind that the sap only moves as fast as your evaporation rate, which is a trickle at best on most rigs. It's in those tubes for a long time.
I figured out that my preheater with 7 2" diameter tubes at about 36" long each will hold about 3.5 gallons of sap. So at 21 gallons an hour evaporation rate the sap would only be in the preheater for 10 minutes.

[Maplebrook]

Dang it! I thought more copper would mean more heat, but then you are right, there is a lot more sap volume in 3/4".....pondering another trip to the plumbing supply store now..

I was wondering about insulating the vent. If your system is closed, doesn't that negate the vent all together? I thought the purpose of the vent was to allow any inadvertent steam to escape, and prevent the pre-heater pipes from bursting catastrophically?

Hi Guys,

I'm no stationary engineer, But I don't think you can boil sap in a preheater that is heated with steam. Even if it did, steam would still have the float box to vent or even push back through the feed line from the tank and gurgle into the sap tank. I've never had an issue with pressurized steam with this set-up.

On my old home made evaporator with two 25' runs of 3/8" copper wrapped tight around the smoke pipe, pressurized steam was an issue. And a vent was required. And I burned sugar inside the 3/8" when the sap started to run out. This set-up would boil sap in the preheater.

I think we get mixed up between direct heat preheaters (pipes containing sap against a flame heat source) and steam preheaters. They are two completely different creatures.

[Maplebrook]

Dang it! I thought more copper would mean more heat, but then you are right, there is a lot more sap volume in 3/4".....pondering another trip to the plumbing supply store now..


Also, for my preheater manifold headers, I drilled 5/8" holes (the o/s diameter of 1/2" copper pipe) at 1 or 11/2" spacing and soldered the 1/2" preheater tubes into them. It was a lot more compact, a lot cheaper and a lot less soldering.

[bmbmkr]

Hello

Perhaps a stupid question but I will ask....why wouldn't a couple of small pipes (SS sched 80) across the exhaust gas flowpath pick up more heat (possibly too much) and be a simpler/cheaper solution? Kind of like a feedwater economizer on a large utility boiler

I've read that a couple member have stainless pre heaters running through their exhaust, and I know there is one manufactured for the wood furnace that i heat my house with to augment the electric water heater. I have these tidbits registered in my nugget for sure! For now, this is my first arch, my skills, and resources are limited, but a good idea for sometime down the road.

[bmbmkr]

Also, for my preheater manifold headers, I drilled 5/8" holes (the o/s diameter of 1/2" copper pipe) at 1 or 11/2" spacing and soldered the 1/2" preheater tubes into them. It was a lot more compact, a lot cheaper and a lot less soldering.

That's a great idea, wished I'd known that,maybe I should have addressed these questions ahead of time, before i went out and bought and cut up 40' of 3/4" lol Thanks for the idea!

[maplesyrupstove]

15307 3/4 pipe with 5/8 holes for 1/2 inch copper pipe

[maplesyrupstove]

15308 7 runs of pipe 45 inches long for preheater

[maplesyrupstove]

15309 15310 drip tray for preheater. preheater with rods to hold drip tray.

[maplesyrupstove]

15311 153121531315314 Got a 3/8 drain pipe on the hood, a 1/2 drain pipe on the preheater tray. No air vent, on my preheater on my D@G hood the air goes up the supply pipe. This one should do the same.

[mol1jb]

That looks great! What material did you make your hood out of?