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Well today after the sap started to flow we installed a leak valve in the sap ladder. The results with the leak valve are good, we now have 22" upstream and the ladder is chugging away. The valve has a very fine adjustment to it and we have set it for the minimum leakage necessary to allow for vacuum transfer.
i remember seeing a study that said the leak valve or pinhole just made the vac level go down, and kinda believed it till i started watching my 6 way star sap ladder with about 55 taps on it. it appears that with the good tight system i have i end up with more sap than air and the sap tends to fill the mainline at the bottom before it can be drawn up the ladder. it would seem logical this would happen as when there is not enough air coming in then of course the sap cant be drawn up, basicly air locked. so i think i will add a small valve to bleed a tiny bit of air in to help it flow, wondering where it should be, near the ladder or at the far end of the lower mainline? was thinking maybe just a saddle with a 1/8 in pipe valve on a short piece of tubing
so today i went out and looked at my sap ladded, it was backed up about 15 ft in the lower mainline, and only about halfway up the sap ladder, had about 18 in vac above the ladder and about 12 below, i took a saddle and a length of tubing and a small valve and installed it a few feet up the mainline a few feet from the lower star of the ladder. cracked the valve open just enough that you can hear a leak if your ear is less than a foot from it, so a very minor leak, and the sap ladder is working much better and not backing up the mainline. i guess i had too tight of a system on the lower part!
how many feet can you pull sap up a sap ladder
well i have always heard that you use roughly 1 in of vac per ft of water column, ie sap lift, so i guess in theory if you had say 20 in vac you could lift almost 20 ft but would have likely no vac at the bottom for the taps
so 56 feet would be asking a lot !!
as far as i know thats not possible, as vac maxes at something like 29.9 i think? so seems that would be about the limit. just curious why ya would need a ladder that tall?
got permission to tap an orchard of about 1000 runs down hill away from the road. Think i will run it down hill and pump it back a project for next year just thinking about it.
It seems this comes up again and again.
There are two sources of vacuum "loss" in sap ladders. First is the friction drop caused by flow of the liquid and gas. Second is the column of liquid.
The intent of sap ladders is to reduce the loss caused by the column of liquid. To do this you must have air/gas flowing in the system. For example, if you have a 10 foot ladder with no air/gas, you have a "solid" column of liquid and this column will cause a vacuum loss equivalent to 10 feet of liquid--about 10 inches of vacuum. However, if for example, the average column content is half gas and half liquid, the liquid column is only 5 feet high, and the loss is only 5 feet of liquid--about 5 inches of mercury.
But if the flow of liquid is fixed, adding gas increases the velocity of the liquid and this increases the friction loss.
Finally, if you are adding air, there will be an effect on the vacuum pump, which depends on the capacity and characteristic curve of the pump.
All this suggests that there will be an optimum quantity of gas/air, and you will have to find that optimum by experiment. Note that the optimum will depend on the quantity of liquid flowing.
The friction loss can be reduced by increasing the cross section of the ladder, which reduces the fluid velocity. However, as the cross section increases there is a tendency for the gas/air to "slip" past the liquid, causing the liquid quantity in the ladder to increase and thus increase the vacuum loss. There is very little slip in 5/16 in tubing, but slip increases rapidly in larger pipe/tube.
Lots of things to think about and diddle to reach an optimum.
I thought I read Dr. Perkins say that 1 inch of hg = 7 feet of lift of water.