How important

[Fred Henderson]

I will boiling last night for the first time with my new everything and I had a slight problem. I had to emergency flood and shut down in a hurry. Everything cleaned up very well. What I did notice is that the float was not letting the sap just trickle in. It would shut off completely. I thought that it should trickle in continuously. I do not have a vapor vent on my preheater but I will have today. Could it have been vapor locking? Is there a rule of thumb as to what size the vent line should be.

[maple flats]

What is the elevation of your feed tank in relation to the evap. Is your feed line large enough? Was the float height set too low? Look at all of these. Also, you might want to pull the rubber seal out of the fill valve and wash it good in plain hot water, might have some sticky on it. Does the valve easily move up and down? I had no vent on my preheater on my old rig and no problems for 3 seasons but it was built so the sap entered on the low side, a slope was then upward and the feed to the evap was then just a straight drop from the highest spot. Built that way no air ever had to push down and essentially the sap into the pan was a drop out an open outlet as the valve opened for more.

[tapper]

Fred,

The vent on the preheater for my 2 1/2 x 8 is 1/2". Make sure you return it back to your feed tank because it will vent enough to spit sap out of it. I have boiled just 3 hours on this evaporator and had pre heat temps over 200 degrees with a constant bubbling out of the vent as if the sap is trying to boil in there. I'm sure it's not but it is awful close to it.

[ibby458]

What a bummer!

It sure makes me want to increase the vent size on mine!

In addition to everything else suggested, I'd call Patrick, too. He might have some insights.

[Fred Henderson]

My feed tank is at 7 feet high. I have approximately 10 feet of 1
1/4" pipe feeding the preheater. The sap goes into the preheater on the low end and rises to the high end and then into the float. The headers on the preheater are both 1 1/4" with 3/4" finn tubes for perheating. Last night I was seeing sap temps of 200 degrees entering the float. I had the float set to manintain a 1 1/2" level. Today when I put it all back together and add the vent line I will try boiling water.

[WF MASON]

Fred I had seen four or five years ago Patrick changed the float valve to one that hinges at the bottom and covers the vertical pipe comming into the float box. Much like maple pro or others use , he said it would allow and maintain pinpoint sap depth during the boil , I found it stops the flow becouse it does shut it off, but it does work. The only complant I ever got was the rear float would only adjust low enough for a 2" sap depth in the flue pan. But the system worked fine. If your not hearing screeching at the float valve , I'd say you don't have vapor lock , but getting sap at 200 degress into your float is 'on the edge' , it has to be vapor lock, I'd run a 1/2" maybe even 3/4" vent pipe to get the air out of there as fast as possible.Don't be afraid to give the float a poke once in awhile to check for air. On the upside ,WOW 200 degrees !!! No complaints there.

[Pete33Vt]

Sounds like vapor lock to me. I am finishing plumbing my preheater today and I am putting in a 1/4" to 5/16 barb fitting as a vent. I don't forsee any problems.As long as there is a vent and its at the high point you shouldn't see any problems.

[Fred Henderson]

Fred I had seen four or five years ago Patrick changed the float valve to one that hinges at the bottom and covers the vertical pipe comming into the float box. Much like maple pro or others use , he said it would allow and maintain pinpoint sap depth during the boil , I found it stops the flow becouse it does shut it off, but it does work. The only complant I ever got was the rear float would only adjust low enough for a 2" sap depth in the flue pan. But the system worked fine. If your not hearing screeching at the float valve , I'd say you don't have vapor lock , but getting sap at 200 degress into your float is 'on the edge' , it has to be vapor lock, I'd run a 1/2" maybe even 3/4" vent pipe to get the air out of there as fast as possible.Don't be afraid to give the float a poke once in awhile to check for air. On the upside ,WOW 200 degrees !!! No complaints there.

The 200 + degrees can only be had by useing 3/4" finn tube radation tubing. The type used in home heating. Soon someone will come up with some finned SS thin wall tubing. I only have 20 feet under the hood.

[Dave Y]

Fred,
200degs can be had w/a convential pre-heater also. last night there were times I had 206 and water was boiling at 208.9!

[brookledge]

Fred
Another possibility is, you have a drop flue with one float(I'm assuming) When the foam rises in your flue pan it can cause your float to shut off because the rise in the level even though the level in the syrup pan is calling for sap.
Just something else to consider.
My pre heater has a 1/2" vent and as others have said with out it being plumbed out of harms way someone could get burned when it vents. My first encounter of mine venting startled me. I got spashed a little but didn't get burned. So best to run the vent back to the feed tank and make sure there is no low spots in the line that could freeze when you are not boiling.
Another thing I have seen is that some put clear tubing on ther vent so that they can have a visual of the level of sap in the feed tank.
Keith

[Fred Henderson]

More than once I wish that I had my old flat pan with the three channels in it. I was use to it and if I burned it I was not out very much. Thanks guys for all the help and advice. I knew I would have a new learning curve this year to go thru but did not think I would get punished like I did.

[tapper]

Fred,

As long as you didnt burn anything or wrinkle any steel you are still in good shape. Get the vent on your preheater fire the rig up slow make sure everything is flowing good for an hour or 2. Then crank her up. It wont be long and you will have the feel for it and you will really enjoy that new machine! I have 3 hours on mine and it already feels like we have been freinds forever.

[danno]

I've got a pre heater on my 30 x 8 for the first time this year and have seen the same problem as Fred. Vapor lock in my situation. You can hear serious hissing coming from the feed line as the pre heater gets real hot.

I just poke the float - but you really have to keep an eye on it. I can crank my hood up and down. If I bring the hood up, the pre heater goes from 195 degrees to the temperature of the cold incoming sap in seconds. Amazing. Also, when the pre heater cools, vapor lock releases and I get a surge of sap at the float.

I don't have a temp guage in the preheater. I'm reading 185-195 in the float box as it's cooling, so I'm happy.

[Maple Hill Sugarhouse]

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[Fred Henderson]

Could it be a defect in the designing of the pre-heater ?. What do you think causes it/What would be a better design??



If I knew the answers I would not be asking ?'s. So far everyone one is being very helpful.

[802maple]

My opinion is the vent needs to be installed

[Maple Hill Sugarhouse]

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[Fred Henderson]

If you have read all the post you will see that this idiot has added the vent pipe. The laws of physics only works if you can prove it. If there is air returning up the feed pipe there may not be enough sap coming in. There would be two forces fighting each other, This is what I mean by proving the law physics.

[tapper]

Yes there is a lengthy thread about preheaters from not long ago this season. I think and dont know for sure because I havnt experimented at all but, the reason for running a preheater on a slight incline is to get more heat out of it. Heat rises and with a slight incline you create resistance so the sap wont freeflow as easy. Even if the preheater were level or low on the outlet end without a vent it is a closed system. Meaning once the float valve closes the system is completly closed and a closed system and a lot of heat mean only bad things.I know my preheater makes a lot of heat fast. That means a lot of expansion fast and the vent gives the expansion someplace to go. Without it it stops the flow and with enough heat possible explosion. But the only way to get that kind of heat is with pressure and there is a reply about that in the more recent preheater thread.

[Fred Henderson]

I will do a search for that thread.

[tapper]

Fred,
It,s on the 2nd page of this evaporators section. I was just there hahaha you will remember it once you get there.

[Maple Hill Sugarhouse]

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[Fred Henderson]

I found it and I still can not beleive what I did. I wrote in that thread that I was going to put a vent line on and never did. They say that when you get older that your mind is the first thing to go and that you are the last one to know.

[Fred Henderson]

Maple Hill, Thanks for all the free advice. There will always be pros and cons to anything that we do. Your theoys do make sense.

[Maple Hill Sugarhouse]

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[WESTVIRGINIAMAPLER]

I do not have a vent on my preheater and it hisses and screams a lot when the sap boils in it, but I don't have any problem with vapor lock. My feed tank is only about 2' or less above float tank, but no problem with head pressure. If it locks, the level in the evaporator will probably drop maybe 1/4" of inch and the presssure pushes the air out and away we go. You may be having a problem with foam in the flue pan. I try to put a couple of drops on both sides of the flue pan about every 15 to 20 minutes. If it is foaming up in there and you don't know it, the level in the float box will not be accurate due to the foam.

To me this sounds like your problem or the design of the float valve prevents it from venting.

[Fred Henderson]

Brandon, If and when we get another run I will do many things differently. I had only been boiling for 1 hour or so when things fell apart in a hurry.

[WESTVIRGINIAMAPLER]

Fred,

I started up the evaporator last year without any defoamer at the sugarhouse and in about 45 minutes I had foam coming out the top of the 15" sides of the flue pan between it and the lip of the hood. Amazing how we forget the little things sometimes. It has happend a couple of times this year with other people boiling for me, seems it wants to foam more this year.

[JasonS]

I just built my preheater this year and I also don't have a vent. I do hear a bit of squealing from the float box as the sap is let in but I have yet to notice any problems with the sap level. I haven't had enough sap to boil continuously for more than 4 hours, Maybe after a long boil I might notice a vapor lock issue?? (This Is my first year with a float box, I thought the noises were normal). I don't really have room to place a vent into the preheater, the high end has two 90 elbows and 2 tees, the four fittings take up almost 12" which is the entire width of my condensate tray. I thought about a vent but figured I'd try to get away without one. Maybe a self-piercing type of valve would work, but I don't know If it would cut into and seal around the fittings.

[Fred Henderson]

You can put the vent in the pipe outside the hood. But all I can say is get one in there. I had to learn the hard way.

[Russell Lampron]

I used a saddle valve on mine for a vent. It only makes a small hole when it pierces the pipe but that was all that I needed. I ran a 1/4" line from that to my feed tank and no more vapor locking.

Russ

[ibby458]

I ended up with a 3/4" copper vent that run up at a 45 degree angle from the high point of my preheater back to the feed tank. With 5 hours of HARD boiling yesterday, it never burped or spit a bit. Neither did the feed line, so I assume the bubbles quietly made their way up the pipe and escaped without taking any sap with it. (It's 8' to the feed tank)

I calibrated all my thermometers before I started. My Internal hood temps ran just a bit over 200 degrees, the incoming sap was around 34 degrees, and the outgoing sap was between 192 & 195 consistently. It didn't slow down the boil a bit!

[JasonS]

I was just getting ready to add my vent to my preheater. I was able to complete last season without one but this year I think I should add one while I have the chance. I'm thinking of changing out a 90 deg. elbow on the high end and adding a tee to the vent line. I was going to use 1/2 for the vent, the preheater is 3/4. I could use copper inside the hood, but what should I use outside the hood to the feed tank, clear flexible plastic? Will this handlethe heat? Should I use copper the entire way? Also I'm still trying to seal my arch door, I have ceramic blanket on the door and the arch front but air/smoke from the blower still leaks out, any ideas?
Any help/ideas are appreciated.
Thanks,
Jason

[danno]

Jason - I use clear hose from my feed tank to my preheater and it works fine. I even use a small 3" peice to connect my preheater copper to my float box - it's copper to copper, but the hose with clamps acts as a sleeve to tie the two together. That gets close to 200 degrees and is still fine. All the hose I use is outside the hood.

I use wood stove flat gasket on my stove doors and ash clean out door. That keeps the spoke, ash and sparks inthe fire box.

[Grade "A"]

Jason, I had a friend that used some clear flexible plastic on part of his vent. What happened to him was that his preheater start to boil inside and it pushed the boiling sap up the vent. When the hot sap got to the clear flexible plastic it made it very soft (almost to melting point). So yes it did work but it was close to failing and if it would have had melted through anyone around could of gotten badly burned. I feel that the amount of money you save is not worth your saftey. I also changed mine all over to copper after that. We all to often find out what works and what doen't the hard way.

[WESTVIRGINIAMAPLER]

Just use some 1/4" flexible copper tubing. Easy to work with and should be plenty to vent a small preheater and run it back to the head tank. Put a quick connect in it so you can disconnect it easily if you want to raise the hood or remove it off the evaporator.

[tapper]

Jason,
I have 1/2 copper to just outside the hood Then I go to a heavy wall clear tubing to the ceiling then back to 1/2 copper dropping back to feed tank. Sure it gets hot but never hot enough to bother the tubing and the clear tube is a good level indicator for your feed tank also.

[super sappy]

You have it correct tapper good work -ss

[Sugarmaker]

I have three small vents at the upper end of my preheater but I just have them dumping into the back pan not to the feed tank. Seems to work OK and all the hot sap and or and steam release is inside the hood.

Chris

[JasonS]

Finally working on my preheater vent. With the way I built my preheater last year I can't get the vent exactly at the highest point. Does it NEEDto be at the highest point or is close good enough. I'm talking about maybe a 1/2" -3/4" lower than the highest point. I think this should work, and I really don't want to redesign my whole preheater. Any thoughts/comments/ideas???
Thanks,
Jason

[Fred Henderson]

It needs to be higher than your sap feed tank. Liquid seeks its own level.

[JasonS]

I was going to run the pipe all the way back to the feed tank. My question was about where the vent connects to the preheater assembly, Does it have to connect at the highest point on the preheater??

[maple flats]

Yes, if you need a vent it should be at the highest point or an air bubble can stop the flow completely before it is vented out. I base this on my years experience with hydronic heating contracting. As I see it the only exception to a vent is if the preheater sap flow is from low to high, with no drop until it is directly over the float valve. If this is the case it would drop down and enter the evaporator ok, any other senareo give the likelyhood of an air block.

[maple flats]

One other thing, if the flow drops any place in the system there must be a vent every time it drops. Most times a preheater is designed to raise from one end to the other and then just have one time the flow drops in elevation and only one vent would be needed.