Brachistochrone curve effects on 3/16” gravity?

[M&M Maple Grove]

As I was walking one of my lines, I noticed a sag and started thinking of the Brachistochrone curve. For those unfamiliar, here’s a link for a detailed explanation: https://en.m.wikipedia.org/wiki/Brachistochrone_curve
or just think how a carnival slide is shaped.

I was curious if there have been any studies on this in regards to 3/16” natural gravity vacuum systems and if it could increase vacuum on the lower taps due to the decreased friction in the lines.

[DrTimPerkins]

The Brachistochrone-curve is useful for the FASTEST descent. In this case however, speed is not the important factor...maximum vacuum at the taphole is. Probably the biggest reason though not to do it this way is that sap would freeze in the tubing below the exit point and block sap flow until the entire line thawed.

This approach can be useful in 3/16" tubing for crossing roads though...and yes, Tim Wilmot (UVM Maple Extension) did studies on it years ago.

[M&M Maple Grove]

I ran 3/16 inch natural gravity for years with great success. As I expand, I ran into some issues with lines not flowing properly and eventually put everything on a shurflo diaphragm pump. Prior to that, I had one line in particular that drove me crazy. Nice slope at the top but flattened out at the bottom. It’s roughly a 500 foot run. The flattening out at the bottom caused back pressure in the lines and sap would seep out on the lower taps. I can’t tell you how many days I spent rerouting that before giving up and going on vacuum. Looking back, I’m curious if mimicking the Brachistochrone-curve at the bottom would have worked. From my understanding, the curve reduces friction and therefore, creates the fastest descent.
I assumed Tim Wilmont would have looked at it as well but I couldn’t find any information on it. Shout out to Tim for all his work on 3/16 inch natural vacuum!

[RileySugarbush]

The advantage or 3/16 goes away when your run flattens out at the bottom. I switch to 5/16 for that portion and try to keep a slightly slope and tight lines for the flat run. It eliminates most of the friction back pressure.


I ran 3/16 inch natural gravity for years with great success. As I expand, I ran into some issues with lines not flowing properly and eventually put everything on a shurflo diaphragm pump. Prior to that, I had one line in particular that drove me crazy. Nice slope at the top but flattened out at the bottom. It’s roughly a 500 foot run. The flattening out at the bottom caused back pressure in the lines and sap would seep out on the lower taps. I can’t tell you how many days I spent rerouting that before giving up and going on vacuum. Looking back, I’m curious if mimicking the Brachistochrone-curve at the bottom would have worked. From my understanding, the curve reduces friction and therefore, creates the fastest descent.
I assumed Tim Wilmont would have looked at it as well but I couldn’t find any information on it. Shout out to Tim for all his work on 3/16 inch natural vacuum!

[M&M Maple Grove]

The advantage or 3/16 goes away when your run flattens out at the bottom. I switch to 5/16 for that portion and try to keep a slightly slope and tight lines for the flat run. It eliminates most of the friction back pressure.
Interesting John. Is that the standard for running 3/16 to a flattened area or was it trial by fire? Does the column of sap hold up/rebuild in the 5/16 or is that the point you lose natural gravity? Looks like some of your taps are set up similar to mine. I just assumed the diaphragm pump would pick up where the gravity left off and take care of the lower level taps as well.