pre heater question

[islandviewpeter]

I have a preheater in the flue pan hood. Sap goes in the bottom and out the top, there is a vent at the high point. Head tank outlet is only about 4" above height of the inlet. I am finding when the tank empties to the height of the vent that the siphon/flow is lost and it won't push the sap through the preheater. Can I prevent this by putting a check valve in the vent line to keep it from sucking air but still allow liquid through if needed. Or simply (or not so simply) raise the height of the head tank. Head tank holds about 80 gal and is feeding through 1 1/4" line.

Thanks

[lastwoodsman]

The preheater vent or air inlet should have tubing or a copper pipe, venting as in mine into the rafters or some back to the head tank. I currently run the tubing into the rafters and into the eaves for venting. Works fine.
Woodsman

[johnallin]

I had a similar situation. I installed a T fitting with a ball valve to bypass the preheater when the tank level gets too low. Keep the valve closed - diverting sap up into the preheater - until the level drops, at which point it is opened sending sap directly to the regulator box.

[Maplebrook]

I agree with Johnallin and the bypass. The preheater needs the weight/head of the sap in the tank to push the sap through.

[islandviewpeter]

Thanks for the input. I think I will raise the head tank some and maybe install a valve on the vent line to close when the level get down to that height. Don't want to bypass the preheater at the height it is right now as I would bypass almost half the tank. Not sure whether I would be able to get the temperature of the sap up high enough to boil inside the tubes with just the steam.

[maple flats]

I have my head tank 24" above the level in my flue pan. The pre-heater is about 12" below the bottom of the head tank or so. On that the sap enters low and exits 6" higher, then it feeds the float valve. It has 4 vents, one on the far end of the entry manifold, 1 on each end of the upper level manifold at tne far end, another on one end of the outlet manifold, plus I have one at the point where the outlet pipe turns down to feed the float valve. The 4 under the hood on the manifolds just have a short nipple and a SS coin vent (used in baseboard heating), the one outside the hood where it turns down to the float valve is about 12" copper tube and then it has a sweat x thread fitting with a vinyl hose (5/16 tubing) that goes up to the rafters, then goes outside to vent. I have no feeding issues.

[johnallin]

Here's a picture of my setup. The bottom of my head tank is about 5" above the regulator box, but below the entry point on the preheater. That's fine until I run down to the last 20 gallons or so in the tank at which point there is not enough pressure to feed the preheater.

Look closely to the back of the pan (left side of pic) and you should see the feed pipe going up into the hood. Right there is a "T" fitting with ball valve diverting the sap up into the preheater (when closed) or allowing it to run straight to the regulator box (when open) effectively bypassing the preheater.

The pipe towards the front is the hot sap exit from the preheater where the bypass hose enters via a second "T". Hot sap from the preheater is blocked by the ball valve, when valve is closed, so it has no where to go but into the regulator box.

It works very well for me, as when I switch over, I'm down to the last 20 gallons in the tank anyway. I wish I could have said this with fewer words; it's not as complicated as it sounds. Good luck with your setup...the preheater is one of the best investments made so far!

preheater 21916.jpg

[islandviewpeter]

Thanks for the picture and further explanation. I'm thinking I will still raise the head tank some going to take some shots with the laser today and see how much it would need to go up. I could also put a bypass line from a drain valve on the inlet tube directly to float box. This would not utilize the float but would give me the safety of directing sap directly to flue pan when getting to the bottom of the head tank.

The inlet and outlet pipes on the preheater are 1 1/2" stainless with sanitary fittings so its a little tricky adding in valves etc.

This is a whole new unit and monday was our first boil. Very happy with results so far.

[islandviewpeter]

Raised the head tank 15", now outlet is above preheater outlet. Should solve the problem. Bonus is head tank sight level is now inside building making it easier to monitor. Now all we need is some sap. Good freeze last night but temperature hanging around 0 degrees celsius nice and sunny, cool north breeze. Takiing the time to add more taps good day to be in the bush.

[maple flats]

My head tank before raising it for the pre-heater install was 10", I raised it to 24" for better pressure.