Head pressure required to feed preheater

[McKenney Maples]

Just curious what people are running for elevation drop between their head/feed tank and preheater or even float box outlet. I'm in the process of building a platform for a 250 gal milk tank, my current roof allows for 6 inches of vertical drop before the rafters become an inconvenience.

Thanks

[maple flats]

I'm not sure what the minimum might be, but on mine the bottom of the tank is 14" above the inlet to the preheater and 9" above the outlet. Then my line goes to the float box. At the float box, I have a 14" drop straight down to an elbow that then feeds the float box. I put 4 vents in my preheater but have never needed to use any, gravity does it all.

[ennismaple]

We have about 4 feet of drop from the feed tank to the preheater. When the tank starts to get low it is noticeable that the sap comes through slower and the levels in the flue pan drop so you need to open up the float valve a bit more.

[buckeye gold]

I'm not sure that a lot of drop is necessary to feed your float box, but if your preheater is restrictive in size then head pressure would be more critical. If You don't have the room for drop then over size your line down to the point of restriction and it should help. It's about weight on any given point, so there are ways to increase weight other than vertical drop, but vertical drop is the simplest.

[johnallin]

There's only about 8" from the bottom of my sap tank to the inlet for the preheater/flue pan float box. When the tank gets to about 40 gal, the sap level is below the highest part of the preheater, so I installed a bypass valve that allows me to re-direct sap to the flue pan float box, bypassing the preheater all together.
I have a clear hose "sight glass" running up along the side of the tank to monitor levels....Works great as long as you're watching the level in the tank.

[McKenney Maples]

I'm not sure that a lot of drop is necessary to feed your float box, but if your preheater is restrictive in size then head pressure would be more critical. If You don't have the room for drop then over size your line down to the point of restriction and it should help. It's about weight on any given point, so there are ways to increase weight other than vertical drop, but vertical drop is the simplest.

Good point. I might have to experiment with some different sized supply lines this winter.

[McKenney Maples]

There's only about 8" from the bottom of my sap tank to the inlet for the preheater/flue pan float box. When the tank gets to about 40 gal, the sap level is below the highest part of the preheater, so I installed a bypass valve that allows me to re-direct sap to the flue pan float box, bypassing the preheater all together.
I have a clear hose "sight glass" running up along the side of the tank to monitor levels....Works great as long as you're watching the level in the tank.

I like this idea. After all I'm only planning on having the tank low during shutdown.

[hookhill]

Most of the preheaters we have dealt with required a small pump to keep the flow consistent and prevent vapor lock.

[maple flats]

My pre-heater also has a by pass, but I only need to use it to drain the feed lines. Gravity works all the time, no pump needed.

[BAP]

Most of the preheaters we have dealt with required a small pump to keep the flow consistent and prevent vapor lock.
Prehearter should not need a pump, but having a vent line off from it to prevent vapor-lock is usually needed.