Sap pre heater

[Clem3]

I am making my own parallel flow pre heater. I am going to use 1" headers on each end. Does the inlet header have to be fed from the middle of the header and does the outlet pipe have to be in the middle of the outlet header? It would be easier if they could both be hooked just to the ends of the headers. I will be using thin wall 5/8 Cu. tubes between the headers. I am planning on using silfos rod for brazing using a CO2 purge to keep the copper from oxydizing inside the tubes. That way there will be no soldering flux on the inside of the tubes. I will also be venting it on the high side of the outlet.

[psparr]

You can feed and exit from the ends.

[WVKeith]

Opposite ends would be best to equalize flow/pressure drop through the tubes.

[Spanielslovesappin]

Feeding and exiting from the ends will be fine. Put the vent at the high point, does not matter which end.

[MT Pockets Producer]

Be sure your vent terminates higher than your head tank or you will get a bath.

[Clinkis]

Is really necessary to vent a pre heater? If so, Just curious why?

[wiam]

Is really necessary to vent a pre heater? If so, Just curious why?

Heated liquid can release trapped air. If enough builds up it will stop sap flow. Seen it happen. Not good.

[maple flats]

Like WVKeith say, feed from opposite ends. Mine works great and I feed the ends. The inlet is on one end and the tubes slope upward, then 2 manifolds are stacked, with the connection at the opposite end, then an upper level slopes up again and the connection is again alternated. This gives the most equal heating of the sap. So manifold inlets are near side, far side, far side and finally near side.
When I built mine I put vents on the top manifold where the #3 is connected above #2, and another at the top on #4 manifold. It is far easier now than later. However All last year I never had to open the vents. My head tank when almost empty is still 23" above the lowest manifold and 18" above the highest. They never air locked. Where the copper tube comes out of the high manifold it goes level until it is directly above the float valve inlet and the hot sap falls in the tube (that is also where I have a thermometer) to feed the float valve.
My previous preheater (on a 2x6) had vents and I frequently had to open the vents. My old head tank was not as high above the preheater and the drop pipe to the float valve was sloped down, not a straight drop. That may have made the difference, I'm not sure.
In operation, I now get 160-170 temps in until the auto draw opens and then it slowly drops to about 120. When the auto draw closes, it takes 2-3 minutes and the temp then reads in the 160-170 range again. I just needed more feet of tubing to hold the temp higher. My manifolds are 1" with 6 @ 1/2" take offs and the length is 52" on the 12 copper tubes that are 1/2" copper.