Pre-Heater

[nmerritt]

Just made a pre-heater to go along with my new hood. Hoping to increase my gph in my 2x6. Has anyone had any vapor locking issues and if so what should I be doing or not doing?

[HanginAround]

Use the low end as the input, so the sap flow and vapour flow are in the same direction. Put a vent on the high end outside the hood, and put clear tubing vertical on it so you can see the level in your feed tank.

[Fred Henderson]

Where does the theory of putting a vent on the high end come from? I am not saying that it is right or wrong. I am just curious.

[tapper]

If I am thinking right on this with the preheater not level it wont fill without a vent on the high end. Or it may not fill evenly creating a vapor lock situation. I think the vent is important too if for some reason the sap were to boil in the preheater.

[oneoldsap]

nmerrit : Tapper is right on the money. You Don't want to vapor your preheater and stop your sap supply, That makes that smell that makes grown men cry.

[brookledge]

I don't know what type of preheater you made but with mine it is a parallel preheater. the sap comes in on the low end and all of the pipes get feed through the manifold equally. the hot sap rises and if it should start to vaporize there is a vent tube at the top that that goes back to my feed tank. And if the float isn't calling for sap for a few minutes or so it has vented before. Also you need to make sure that the vent pipe isn't going to squirt boiling sap onto you and burn you.
If you don't have the vent on the high side and it does start to vaporize the gasses are going to try to go up and it will compound the situation.
Keith

[HanginAround]

The vent gives vapour a place to go from the highest point in the system. I don't think it's strictly necessary, but if your worried about vapour lock, I think it's a good idea. Here's a pic of a commercial one, the cold sap comes from the black ABS. After looking closer, I see the vent/sight tube is on the cold/low side (right near the ABS/SS junction), so I guess my theory goes out the window there, there is no vent on the high end. Maybe the plumbing is big enough and the flow high enough, they don't worry about it on these. The ball valve below the vent is a preheater bypass, so you can drain and bypass the preheater when sap gets low.

http://personal.nbnet.nb.ca/peteb/maple/HPIM0517.JPG

[WESTVIRGINIAMAPLER]

I don't have any on mine and I don't have a problem. Any time there is vapor lock, the evaporator level will drop slightly and the float control will open completely that with the head pressure, it has to come out. If I were running my pans 1/2", then if it dropped 1/8" or 1/4", it could create a problem but with running them 1", there isn't any issue.

I think the key is sufficient head pressure. If you have very little head pressure, you may need a vent.

[Russell Lampron]

I have mine set up just like Petes picture. I use the drain to empty out the pre heater when I'm done boiling so it doesn't freeze and split the pipes in the pre heater between runs.

Russ

[Fred Henderson]

If a vent pipe coming off the high end of the preheater goes back to the heigth of the feed tank then that vent pipe has the same level of sap in it as is in the feed tank. So my question is how will this allow any vapor to escape?

[HanginAround]

Vapour will still go upwards in a liquid, regardless of how deep it is. But to be honest, not many have a vent, it was just my own thoery as a good way to solve vapour lock issues, and I was thinking the commercial ones were vented on the high end. I would still do it though I think.

[Fred Henderson]

Vapour will still go upwards in a liquid, regardless of how deep it is. But to be honest, not many have a vent, it was just my own thoery as a good way to solve vapour lock issues, and I was thinking the commercial ones were vented on the high end. I would still do it though I think.



The reason for the vent which is usually a very small dia is it act as a pressure releif valve. Loosing very little heat.

[danno]

Have people experienced vapor lock on their preheaters.

I've got 50' of 3/4 copper refirdge. coil that I'm installing as a preheater. My first notion was to run the sap feed line into the preheater on the higher line because the sap tank is higher than the float box - and figured at the end of the day it would be easier to drain as everything would be flowing downhill into the float box. After reading this thread, maybe I should reverse that thought?

I did buy a piercing valve to install on the line to prevent vapor lock, but have not installed it yet.

[Fred Henderson]

I think that it has almost got to go from tank ,to preheater ,to float, don't see how it would work anyother way. Unlees you want to preheat it and put it into another tank in which case it will sour very quickly.

[danno]

No Fred, that's not what I mean. I'm still planning on having my storage tank feed the pre heater and the pre heater feed my float box.


What I was considering changing after seeing these posts is having my holding tank enter my preheater on the low side and have the sap exit the preheater to the float on the high side.

My original assumption was that as my holding tank is higher than my float box, let the sap enter the preheater from my storage tank on the high side and let the sap run downhill through the preheater into the float box.

Will the "downhill" effect by negated by vapor lock and heats desire to rise?

[WESTVIRGINIAMAPLER]

The problem with downhill flow is that is it going to take the path of least resistance like the center pipe and the sap will not heat even and when it has to push uphill, you get even heating of the sap.

I don't know if this is correct as I have never tried it, but this is the way I understand it

[Fred Henderson]

Brandon, I can agree with that theory. Pushing up hill is basically the way a parallel works.

[Fred Henderson]

Danno, Where are you putting that copper coil? Do you have a steam hood?

[Fred Henderson]

Brandon,

Please clean out your mail box. I jsut tryed to PM you and couldn't.

[brookledge]

The reason for the vent is this. When the float is calling for sap and the flow is moving along things are fine but if the flow stops to long and the sap does boil in the preheater than it needs a way of relieving the pressure. If your float has a good seal and will not let any sap out, the pipe will begin to build pressure. If your sap doesn't boil then there will never be a problem.
But try to boil water in a closed container,. it will explode.
May be instead of calling it a vent it could also be called a pressure relief.
If your preheater is running near boiling temp and the float shuts off it can blow off fittings or hose clamps.
As for me on the average mine vents once or twice a year.
Keith

[Fred Henderson]

I don't see how that steam can get over 211 drg in an unsealed hood, but maybe someone could explain how it does.

[HanginAround]

I don't think it can boil in a preheater either, a physical impossibilty without having pressure in your hood, but there is a lot of air/gases that comes out of solution as the sap heats. You also rarely will have pressure higher than the head pressure since the system is open on the feed end. The only time there is pressure higher than head pressure is if you stop the flow suddenly, you can get water hammer effect, wich can be significant, but I don't think enough to blow anything, just makes water bounce a bit in a sight tube.

[WESTVIRGINIAMAPLER]

Fred,

I got the notification about your message being rejected in my email and cleaned it out. I tried to send you a message back but your PM is set up to block all incoming messages and it wouldn't let me send.

[danno]

Fred, in answer to your question, I'm putting the copper coil over the flue pan and under the steam hood. The copper coil is staying in the coil shape except obvioulsy where it runs out the hood for sap input/output. I've put some spacers between the coils so that the steam can work around them.

I'm using an aluminum, round hot water heater pan to catch and drain the condensate off the copper. The whole set up with 50' of 3/4 coil will run under $100. Thought it was a deal with the current price of copper and at 50' should be able to get the preheated sap good and hot.

The "relief valve" I've got requires me to back it out if I neet to vent the system. It is not automatic. It is self piercing into the copper. What have others used for a relief valve on there pre heaters?

[Fred Henderson]

Fred,

I got the notification about your message being rejected in my email and cleaned it out. I tried to send you a message back but your PM is set up to block all incoming messages and it wouldn't let me send.

I will check it out.

[WESTVIRGINIAMAPLER]

With 50' it will be coming out at 211 degrees with that size evaporator.

[brookledge]

Just to further explain why the sap can boil in the pre heater. If you have a hood and it has a damper in it when you close it, it will increase the pressure inside the hood. The first year I used my preheater the sap coming out was around 180. I was told that I would probably need a damper but didn't put one in that year.
The next year I put one in and quickly found out I could barely close it or else the hole hood would rumble and shake. By closing it just alittle my sap temp coming out of the preheater shot up to the low 200s. If I close it any more it will boil in the pre heater.
As for steam temp steam under 2 lbs = 218
3 lbs = 221
4 lbs = 224
5 lbs = 227
6 lbs = 230
Another thing to remember is a pressure cooker on the top there is a weight. With usually 3 different settings. The reason it cooks food so much faster is because the steam temp is increased. 10lbs =240 and 15 = 250
If you are not using a damper than the pressure inside the hood will always remain atmospheric pressure but add adamper and close it too much and watch out
Keith

[RileySugarbush]

You better watch out if you get 6 lbs of pressure in a steam hood!

On a 2 x 4 foot hood, even 1 psi will try to lift the hood with over 1000 pounds of force! The limit on pressure is the weight of the hood devided byt the area of the hood, and that's probably the pressure rattling Keith's hood. Youd have to bolt it down to get more, but don't do it. 6 psi would blow it up.

It's more likely that the damper minimizes the inflow of cool air around the base of the hood and allows the steam to heat the preheat tubing to close to boiling. As mentioned elsewhere, close the damper until the steam is just licking out the bottom edges.

[Fred Henderson]

Keith,
You mean to say that your hood is air tight. When you close the damper all the way shut is there no steam leaking out around the edges.

[danno]

One thing I've always wondered, by putting a damper in the steam stack and thus reducing the steam escaping up the stack, are you reducing your GPH ?

[brookledge]

Fred
When I close my damper it pushes out the sides alittle and thee steam pushes out all the cracks I have to keep my doors on the hood latched or they raise up. May be this year I will try to monitor the temps in the hood
Keith

[Fred Henderson]

OK, all I got to do is add a small copper line back to the feed tank. The fitting is already there on the preheater.

[brookledge]

I've thought about that also but I feel like it uses more energy to raise the sap up to boiling temp than is lost by holding the steam in. That would be a good quetion for a physics professor.
With it taking 1 btu to raise 1 pound of sap 1 degree it would seem that the hotter the sap is coming in the better but I'm not sure how to tell if by dampening the hood is reducing boiling capacity either.
Keith

[HanginAround]

danno, if you close it part way as Riley says, I don't think there will be much negative effect, but technically, you are right if you closed it too much, and currently manufacturers are recommending running them wide open.

Brook, thanks for the additional info, I'm surprised the boiling point is as high as it is at 2 psi. I can't really see getting even 1 psi in it though, as the force is so great, as Riley says. There are two more factors to consider, the first being that the head pressure increases the boiling point in the preheater by the same factor as you stated, so if you have 2-4 ft of head, you should have 1-2 psi in the preheater. Not sure since it is a dynamic system, the float valve partially open lowers the pressure slightly than if it were closed, but regardless, I think you would always have more pressure in the preheater than in the hood. The second is the sugar content in the sap increases the boiling point slightly (much less than one degree). I wouldn't swear to any of this of course :) But I'm leaning about 90% towards that it can't boil.

[Fred Henderson]

I've thought about that also but I feel like it uses more energy to raise the sap up to boiling temp than is lost by holding the steam in. That would be a good quetion for a physics professor.
With it taking 1 btu to raise 1 pound of sap 1 degree it would seem that the hotter the sap is coming in the better but I'm not sure how to tell if by dampening the hood is reducing boiling capacity either.
Keith




Brook; Do you have a vent line going back to your feed tank?

[tapper]

Thie topic is very interesting. It looks like a project for the Mythbusters?

[Fred Henderson]

The topic is very interesting. It looks like a project for the Mythbusters?

Its a good place to learn, kick ideas around and so on. Where as I do not disagree that some pressure can be built in a preheater. I just don't know how much. I know that the equipment dealers do sell a temp/pressure relief valve for the preheater. Its along the same lines as one on a water heater but with much lower pressures, I think.

Tapper: Do you think that one engineer designed the space shuttle solely on his own ideas?

[tapper]

Fred,

Nope. and the shuttle is a new experience every time too. They are never sure if its going to get there let alone make it back. You pay your money and you take your chances. I bought a thermometer to go in my preheater line today. I should have bought one that measures pressure also but thought there might not be enough pressure for it to register.

[Fred Henderson]

Tapper;
Is your evap a drop flue? That thermometer sound like a good idea. I will look for one from my old friends McMaster/Carr company.

[tapper]

Fred,
Yes it is a drop flue. The inlet line into the float box is 1 1/4" copper And Im going to install a T either in the elbow or the short drop into the box. The thermometer is a Winters has a 2 1/2" dial ,1/2 npt, a short stem and a range of 30 to 250. You can get them that show both temp and pressure. McMaster Carr doesnt have as big of a selection as Grainger. I bought mine at a heating and plumbing supply store and paid $16.00 for it. The clerk said it listed for $29.00 he cut it back to $16.00. If you can find a thermometer with a short thermowell you can install the wells at different places on the evaprator and use just 1 thermometer. I tried to find just that but its tough for me to buy from a pic on the internet. Actually I have 2 like a wanted but the range on the thermometers arent high enough.

[Fred Henderson]

I can not buy from grainger without having an account with them. I can usually find what I want in McMaster catalog. When I retired the place that I worked got me a new catalog for them. I buy a lot of stuff from them. No matter what temp I get out if my preheater anything will be better than nothing.

[brookledge]

Yes my vent goes back to my feed tank. My preheater is factory made from leader and it came with it.
Also when I was referring to pressure I was talking about inside the hood not inside the preheater pipe.
Like I said I will try to monitor the pressure and temp inside my hood this year
Keith

[Fred Henderson]

Brook ,
Now this throws a whole new light on things. What size is the line going back to the tank?

[brookledge]

My vent line is 1/2"
Keith

[danno]

Can you guys give me an idea of the type of vent you are using that you have piped back to your feed tank? Is it "T"'d into your copper or a piercing valve?

[Breezy Lane Sugarworks]

Mine is tee'd into the hot sap line. Also 1/2 ". It doesn't need to be big diam. because it is just for air bubbles to relieve through.

[tapper]

Danno,

Click on the link in my signature it will take you to my pictures. In the newer sugar house album there are a few pics of the preheater. pic #2673 and 2674

[Fred Henderson]

Is the vent pipe in the pipe going to the float?

[tapper]

Fred,
The paralells are t'd together at top and bottom with a square copper tube .The vent comes off the top of the top end square tube and is directly above the feed to the floatbox. This preheater is made by leader. Thats the way they make them. I dont think there is a reason they cant be t'd together with regular tubing.

[WESTVIRGINIAMAPLER]

I would love to see a factory preheater and see how it stacks up against my homemade.

[danno]

Jon, hard to see the preheater pics, but aside from that, GREAT PICS. I just love to the transition from the outside cooking to the new sugarhouse and evap. Nice looking set up!

[tapper]

Brandon,
Looks to me that you may have more copper in your preheater. Nothing wrong with that. Other than the manufactured one having square tubes at each end I see no difference. I think leader may save cost by fabricating it this way instead of using that many fittings. I will take some better pics and post them later today.

[tapper]

I uploaded preheater pics to my site. there are a few of the thermometer I installed in the preheater line this afternoon. Once on the site double click on each pic and a larger one will come up.

[Fred Henderson]

Tapper:
I went there and I do not see them. All I get is a total of 27 pic's.

[tapper]

ok try now it should work?

[danno]

Tapper - now that's some copper! Hard to tell if it's the pic or large diameter copper - looks like big copper. I like the temp. add on as well.

[Sugarmaker]

Tapper,
You will like the thermometer that you added. I added a preheater that I built myself copied after Leaders design. Although I only saw the picture in the book. No problem getting 200 degree F sap entering the float box. :cool:
Chris

[tapper]

The inlet and outlet are 1 1/4" and the paralells are 1". I am getting anxious to try this thing out. Still waiting on some parts from Leader or I would have test boiled it by now.

[HanginAround]

Wow, looks awesome.

[Fred Henderson]

Nice looking set up. My parallels are 3/4" fin tube radiation. With this type if tubing I should see 211 drg entering the float. I maintain that the smaller the column of liquid the easier it is to heat that column. I design one this way for a friend and he see 211 drg easily.

[ibby458]

Another way to look at it is: The larger the tubing, the longer the sap stays in the preheater before hitting the float box. I have a bunch of 3/4 fin tube, so that's what I'm going to use as well, but an interesting test would compare a 3/8 preheater to a 1" in the same evaporator. Of course, with the price of copper, who could afford to test different sizes?

[JasonS]

When you guys say,"Fin tube" does that mean the copper pipe used in baseboard heat situations? I need to build a new preheater for my new leader, just looking for tips. Fin tube sounds like an interesting way to go.
Thanks,
Jason

[Fred Henderson]

yes. fin tube as in baseboard radiation. The copper pipe used in those are very very thin and this allows for good heat transfer. Plus the Alu fin is an excellant heat transfer metal.

[JasonS]

Thanks for the info Fred. Sounds like a no brainer to me, Does anybody have a negative to using fin tube? Looks like only positives,unless I'm missing something??
Thanks,
Jason

[brookledge]

Tapper
That is the same preheater I have. I put a tee witha 1/2 ball valve on my inlet line just before it enters the hood (inlet is lower than outlet) so that when I'm done boiling I can open the valve and drain the preheater right into my float box. Otherwise you need to take the supply line off to drain it.
You got a good pic showing the vent pipe.
Keith

[tapper]

Keith,
Thank You for the tip!! That sounds like a very good idea and I think I will do the same before the 1st boil.

[Russell Lampron]

I put one of those self piercing valves like you use for an ice maker in my inlet line to drain it into the float box when I'm done boiling. I also put one in my outlet line for a vent in case of vapor lock.

Russ

[mapleman3]

Anybody make their hood out of aluminum?? I can make mine myself for a couple hundred vs the 500-1000 everyone else has quoted.... is aluminum safe as a steam hood???

[tapper]

Jim,
The hood I made for the fluepan on my 2x6 was aluminum. I used it for 10 years and it worked great. Like a dummy i never got any pictures of it tho. The people that bought it from me have a few posts on here. I got the aluminum out of the scrap yard and bent it up on a trim brake. it was too heavy a guage for the brake but I did it anyhow. I dont think I had any more than $10 .00 in it when it was done.

[Dave Y]

Jim.
The hood I have over my syrup pan is aluminum. The folks I bought it from used it for a long time.

[Russell Lampron]

There are alot of aluminum hoods out there. They aren't as shiney as stainless but they cost alot less.

Russ

[WESTVIRGINIAMAPLER]

Leader makes both or did a couple of years ago.

[mapleman3]

I'm thinking I could make it real nice.. may have to rivit it. I could silver solder the joints to seal it especially so the condensate drips into the drip channel and not in-between that and the side of the hood.... hmmmm I just may get started on it this weekend. I'm not so much needing it 100% shiny just nice-clean and functional..... isn't the sugarmaker supposed to be somewhat thrifty???? if I spend big $$ every year in improvements I'll never make a dime ha ha ha

[tapper]

Jim,
If you have a brake or access to one you can do a nice job on it. The one I made was rivited together and I kept it clean with alumabrite but not sure if you can get that stuff anymore?

[mapleman3]

Did you seal the seams at all???

[tapper]

The only seams I had were in the corners and no I didnt get them sealed up very well . I had good overlaps rivited tight and may have used a little caulk on them but eventually they leaked a bit. I ran the hood a little out of level to one corner and had a small metal trough under that corner that caught all the condensate. That part of it wasnt that pretty but it worked.

[brookledge]

Jim
My hood is also made of aluminum. As far as the seams go it was made by leader and they are rolled over and pressed by a machine so they are pretty tight. The seams especially around the doors will leak when I close the damper to get it hopping.
Keith

[Sugarmaker]

Jim,
Go for it. Don't worry a lot about the seams being sealed absolutely tight it will only leak steam if you have positive pressure under the hood from a damper in the stack. I bent my stainless steel hood on the shop bench with a very crude jerry rigged manually brake and s soft rubber hammer. all the joints are riveted. The most money I had in it was the stainless hinges I bought from McMaster Carr. Having boiled both ways with and without a hood I would not want to go back to a steamy boiling room.
Chris

[Russell Lampron]

Jim,

Do you know someone with a welder that can weld aluminum? You could get the hood built and bring it to a welder and have the seams welded in places where it would leak. Mainly the drip tray around the edges and in the corners. The rest of it could be riveted with a little dab of the DAP sealer on the rivets to seal them.

Russ

[mapleman3]

Well I'll see how it all works, I will start building my hood and preheater this weekend... it may not end up as shiny as the pans but it will be functional.... I don't want to boil without a hood this year, I want the 15+ % or more that everyone says they get. !! plus that good ole free hot water!

[tapper]

I tried to boil without the hood on my 2x6 once just for the heck of it. It didnt take me long to put it back on.

[JasonS]

I'm in the process of building my preheater and I had a stainless condensate tray made by a local HVAC guy. I made a mistake and gave him the wrong measurements!! Therefore I now have two condensate trays and a large hole in my pocket!! The one that is too big is 40" x 18" and 1" deep, any ideas what I could use this for or does anybody want to buy it? I paid way too much to just throw it out or let it sit in my basement for 20 years. There is a 1/2in male NPT fitting soldered into the right rear side of the pan/tray.
Any Ideas??????????????????

[Fred Henderson]

I'm in the process of building my preheater and I had a stainless condensate tray made by a local HVAC guy. I made a mistake and gave him the wrong measurements!! Therefore I now have two condensate trays and a large hole in my pocket!! The one that is too big is 40" x 18" and 1" deep, any ideas what I could use this for or does anybody want to buy it? I paid way too much to just throw it out or let it sit in my basement for 20 years. There is a 1/2in male NPT fitting soldered into the right rear side of the pan/tray.
Any Ideas??????????????????

There is a member here on the Trader that might want it . His name is Ibby 458. You want to PM him.

[JasonS]

I don't think anybody is interested in buying my extra condensate tray, so there must be someone who has an idea on what I could do/make with it.

[ibby458]

I was looking for something in a HVAC catalog, and came across some automatic air vents to bleed the air out of heating systems. THey're a brass chamber with a float that drps down to allow air to escape. Once the air is gone, the float seals the opening. Why won't these work to vent a preheater?

[Fred Henderson]

I think they will but I am not sure about them if they are in the hot steam. We had them by the thousands where I worked.

[brookledge]

Sounds like someone should try one, it seems like it should work
Keith

[ibby458]

I think I will! They're pretty cheap, and easy to install. If it DON'T work, I'll find out in a test boil and can replace it before the sap runs.

I got the fin tube all cleaned (Round brush on a lot of drill extensions, spinning like crazy while my wife poured soapy water into the tube.) It's all nice shiney copper inside now.

I'll end up with 25' of 3/4" fin tube in the hood. THat oughta heat the sap up good!

[Jim Brown]

Well we got the new steamaway working yesterday. Boy what a piece of equipt.As far as i can tell we were getting about 52 gallons per hours at 600 degrees at the stack base.Pertty good for a 2x6. All I do know is we boiled 75 gallons of water out of the stock tank in 1 hour and 35 minutes. BRING ON THE SAP!!!
Going to put an in-expensive water meter on the sap line then we will know for sure
Jim

[Fred Henderson]

That is good Jim. You always feel better when you know that your investment is going to work.

[danno]

Jim, if you are looking for a water meter, go see your town water dept. Someone on the forum recommended it - so I thought I would give it a shot. Walked out with a free, brand new water meter which I have since installed in-line on my sap supply line.

[WESTVIRGINIAMAPLER]

Jim,

What were you getting before adding the steamaway??