Preheater drip pan question

[Minnesota Tapper]

After reading the great posts about steam hoods and preheaters I'm in the process of making a hood and preheater. I bought a s.s. sheet to make the hood. It will sit down tight on my 2x4 flue pan. I will make a parallel flow copper preheater to fit in the flue hood. Plan is to slope the drip tray to the rear water channel in my hood. I want to make a single,flat, long rectangular preheater drip pan under the preheater. If I do 6 "loops" of copper pipe the drain pan would be 12" wide. If I go 8 "loops" of copper it would increase the width to 16" wide. The question is how wide can i go before it inhibits the steams ability to rise around the drip pan? Does the rising steam from the flue pan not build up moisture under the drip tray which would then drip back into the sap? Should I slope the drip pan towards the rear at a high angle? Thanks for any insight. Pictures would be amazing

[Haynes Forest Products]

Any pan under the preheater will inhibit the steam flow. Its just a matter of how much. I designed a preheater tray with Jim at Smokey lake that is about as unrestrictive as you can get. It consists of individual channels for each tube with lots of steam ports for full flow of steam up, thru and away. I came up with the design after making different style trays all of them very simple flat cookie sheet type of trays but all were very ineffective.

I know this wasn't very helpful as far as how you should make yours BUT the less the steam has to flow around the tray before it hits the tubes the better. Remember its the clear steam you cant see that is the hottest so that is where you want the prheater. Plus the more you restrict it in the hood the slower it will vent out.

[RileySugarbush]

You can arrange some of your parallel tubes vertically to minimize the width of the drip tray. Tat is what I did on my old 3' flue pan. I have a version of the Smokey Lake drip pan like Haynes mentions here in Eden Prairie if you are close and want a look.

[Minnesota Tapper]

I know exactly what drip tray you guys are talking about. I was more under the understanding that I didnt need the separate drip channels with steam perforations because I was using a hood to hold the heat around the copper tubes . But that makes sense. It would also allow me to go wider with more tubes in the preheater without obstructing steam flow/venting. Be a little more work to make individual channels but I'm sure long term benefits will be worth it. Thanks for the help. And the offer to see your preheater rileysugar. I'm west of the cities in Delano. I would take you up on it if I was closer. But I know what direction I'm going to go with regards to the drip tray now.

[maple flats]

My pre-heater is double decker design. I used manufactured manifolds made for hot water heat, each consists of a 1" header with 6 take offs of 1/2". (if you use Tees the unit ends up much wider and thus further restricts steam flow.) The inlet is at the low end near the float box. From there the header reaches toward the opposite side, it is about 12-14" long https://www.ebay.com/itm/2-3-4-5-or-...91tODNdafqelyg I found mine on Ebay for about $21-22 each back about 8-10 years ago.
Then each of the 1/2" x 54" copper tubes extend toward the far end of the flue pan and rise 1.5" to another manifold. From there the water rises to another the same and returns to above the first manifold where the heated sap exits and flows past a thermometer and then to fill the float box. The sap flow enters the near low end, rises and goes up to the 2nd level at the opposite corner. From there it rises another 1.5" and exits above where it entered, thus I have 4 such manifolds and 12 lengths (6x2) of 1/2" copper. From where the heated sap exits the heater it has a very slight slope downward (maybe a 1/2" fall in the 12-14" it runs to a vent T with a 6" stem thermometer screwed in, then the sap drops straight down to an elbow that feeds the float box. It heats the sap to about 170-180 F until the auto draw opens, and then the temp falls to about 110-140F depending on the length of the draw. I will likely never change it, but I think I might get more heat exchange if the header was 1.25 or 1.5" instead of 1" and the lengths of copper were 3/4" instead of 1/2". At each corner and each level I installed a coin vent. However, my head tank is about 18" above the heater and I've never had to vent air. I would still have the vents.
Under the entire heater I have a sloped flat tray with 1" sides and the low end rests on the gutter near the stack.
Use water soluble flux and clean it well with HOT water after soldering to remove the flux. My tray is solid but I bet it would heat better if I had steam vents in the tray like a Smoky Lake tray.
I have a drain valve directly above the inlet float box and I drain the heater every time I shut down after a boil. I only clean the inside about every 3-4 days be hooking a hose the force hot water thru and it drains to a bucket.
A pre-heater works best if you have a damper in the steam stack, close it until you just start to get steam leaking out under the hood. That puts the heater in the most steam. Also have it so the tray is under the steam stack to catch drips out that or have a wide shallow funnel under the stack and run the drips to the gutter on the hood.

[Minnesota Tapper]

Mapleflats I think I may have to steal your inline thermometer idea! One issue of individual channels is catching the condensation that will drip from the steam stack. With a flat pan it would have been wide enough to let the condensation just drip from stack to the pan. I could build a funnel under the stack . But how do you guys get it from the funnel to the hood gutter? Is there some sort of flexible tubing that could take the heat ? Or do something with s.s.?

[RileySugarbush]

In my old vertical parallel array, (think rail fence), I had the inlet on one end at the bottom of a manifold ( fence post) , then six 3/4" tubes running slightly up hill to the other end ( fence rails) that had an exit on the top end and a vent. 6" wide drip tray under it with a soldered 3/8 tube that ran in to the hood gutter. My steam stack was 8" so I put some deflectors on the connecting to the hood to make the side drips hit the tray and not miss. Kind of a part funnel. The tray hung from the bottom rail. This worked fine but needed the vent.

[maple flats]

My hoods have 2- 15" stacks. The stacks on the syrup pan and the flue pan have a shallow funnel that came with the hoods. I had to make a channel to hang off the bottom of the funnels. They both are run into the gutter nearest that funnel. The syrup hood is attached to the flue pan hood but each is a complete hood. The gutters on the front hood have a 3/4" fitting and each has a plug installed. I removed one plug on the front hood and one at that corner on the flue pan hood and I connected them with copper pipe. Then at one corner at the back of the flue hood I connected a barb x MPT adapter and a length of 3/4" vinyl tubing hangs down into a bucket on the floor. I need to empty the bucket about every hour or it over flows. Had I planned ahead I would have a floor drain there. Before I had a tankless water heater I used the water in the bucket for some cleaning, I now just use permeate pumped thru the tankless heater.

[Minnesota Tapper]

Not to bring up a dead horse. ..but this is what I came up with all the advice. 1-1/4" header tubes with 6 -3/4" runs. Smoky lake style drip pan. Worked well. Ran 180-190° with consistent drawoffs. When a big shot of sap came in it would get down closer to 165°. Took alot longer to make than expected but well worth it. Only change I need to make is replace the little 6" steam pipe on my front hood to a 10" like the flu pan hood and itll be perfect as I can make it. Hope the pics work.20190213_022341.jpg20190218_162533.jpg20190325_150921.jpg