How many sap ladders?

[Danielb]

I am planning on running tubibn through a small bush this winter, around 400 taps all said and done. I don't think i will have enough slope for a 2% slope on my mainline, so i am looking at sap ladders. I will have 7cfm vacuum pump attached with releaser and moisture trap at a couple of 250-gallon dairy tanks for in-woods storage.

My question is, can you have more than one sap ladder on a length of mainline? Is it better to have more, shorter ladders, or fewer with more rise?
How many smaller tubes should one use for the ladder? I will have 3/4" mainlines, likely 2 splitting the total taps. Should 6- 5/16 lines rising at each ladder be sufficient, or should i have more?
School me, this is all new to me

[maple flats]

If you keep the lines tight (very few leaks) you can have more than 1 sap ladder on a main. In fact on my small system I have 2 ladders on one main and 2 on another. With each ladder you will lose a little vacuum, but if done right it will be very little.
My pump gets 27" vacuum at the releaser. On my longer main (1") if the leaks are near zero I get 25-26" at the far end of the main and 24" at the farthest tap. My smaller main , also 1" but after the last of 2 sap ladders it goes to 3/4" (only because it was 3/4" before I added about 150 more taps, I had to swap the main to 1" from 3/4 for about 30' in one direction and 40' in the other. The sap ladder is in the middle of that line). After the sap ladder over a driveway the slope in about 5% all of the way to the releaser and it flows well, so I never changed it. I do believe I could have 3 or 4 sap ladders if needed. My sap laddersare all in the range of 8-11' each
All this being said, I don't know how many CFM my pump moves, it is an old Babson Bros BB4, and I've never seen specs on it. It is a piston pump. The BB4 was a forerunner to Surge pumps, I believe it would be similar to an SP22 by Surge.

[TapTapTap]

Theoretically, the system will loose about 1" of vacuum for every foot of lift in the ladder. I say theoretically since the slurping effect will allow some vacuum to slip by.

[maple flats]

Tap, tap, tap, how is it that I get vacuum after 2 sap ladders, an 8' lift and a 11' lift when at my releaser I have 27" and at the end of the mainline I have 25-26" and at my end tap I get 24"?
I am using spider type ladders using 5/16 tubing. I have 1 leg for each 15 taps or part there of. For example I have 3 legs on one having 41 taps. On both mains I have a micro leak set up to help the flow climb, but only on the farthest out sap ladder. The ladder closer to the releaser doesn't get one because it got a tiny amount of air at the farthest ladder. To run my micro leaks, I have a little needle valve and it gets opened just until I can hear air flow when I have my CDL leak finder. I just looked it up and was going to link it here, but it turns out CDL no longer offers them.
Speaking of my leak finder, I had a leak at the releaser last year but couldn't find it, until I used my CDL leak finder. It was easily found and very obvious even though the vacuum pump was 4' away and that is quite loud.

[TapTapTap]

Dave -
Here's my take on it:
On one level it's simple physics. Every inch of mercury equals 13.6 inches of water (roughly 1" Hg = 1' H2O). However, like i said, the ladders slurp which allows some vacuum to escape past the ladder which was the point I was trying to make. The ladder lines also contain air bubbles that reduce the effective weight of the liquid column. By design, this effect occurs even more with multiple small lines in the ladder that are pulling at different levels and allows additional vacuum through. But when the sap is running hard, the ladder works at near capacity and the lines fill up to near full height. At that point, the vacuum loss equals about 1" of mercury. As sap flow slows down, the average liquid level in the lines drops (by a lot) and more vacuum slips by. I have a ladder right next to my driveway with vacuum gauges at each side and I see this effect frequently.
Ken

[JoeJ]

After working for several years to eliminate 3 sap ladders in my sugar house woods, I would suggest getting a good transit and determining the grade drop that you have to figure out if you have enough drop to go to 1%. I got rid of one sap ladder after some line design by re-routing the 1" line at a regular 2%. The second sap ladder was eliminated by setting 520' of line at 1% and the third was gone thanks to an electric releaser to pump up the 14' rise. I would much rather have a 1" mainline set at 1% than have to deal with a sap ladder.

If you are able to get the 1% grade, you need to use 1" main line kept very tight with pipe tensioners with no sags in the line to freeze.

Joe

[n8hutch]

If you must use Ladders, 2, 6' Ladders will out perform 1, 12' Ladder, Ladders need maintenance and adjusting so i like to keep mine at a reasonable working height.

[Danielb]

Thanks all. Lots of information to hash out.
Just by a preliminary survey of the woods, i should need about 6-8' of rise, but i will be bringing a transit with me to run my mainline.

[DrTimPerkins]

If you are able to get the 1% grade, you need to use 1" main line kept very tight with pipe tensioners with no sags in the line to freeze.

I wanted to emphasize what Joe said because it is a very important point for mainline on flat ground. It is possible to run mainline down to 1%, but you need to keep it very tight on wire, with a lot of wire ties, no sags, make sure there are no ripples, and be sure it is laid out with great attention to grade.

Going up one pipe size can make a big difference. Example.

Say you have a 3/4" pipe that at peak flow is 1/2 full of sap. A sag as small as 1/2" means that parts of the pipe will be completely full of sap at that time and there will be some amount of build-up of sap beyond that point. On gravity this isn't a major problem, but if you are using pumped vacuum, air transfer (to generate vacuum) will be slowed down, and vacuum will go down beyond that point.

A 1" pipe on the other hand, with the same amount of sap flow, will fill the pipe only about 1/3 of the depth. A 1/2" sag will still provide enough room for air to slip by the sap across the top. Air movement is unimpeded, and during that peak flow you will also maintain peak vacuum.

This is also why 1/2" pipe on a pumped vacuum system doesn't make much sense. There is just not enough room for error, especially during peak flows. Tubing systems should always be designed to manage your peak flow. Otherwise you end up with the equivalent of a sap traffic jam...poor sap movement...and reduced sap yield. Of course there are good reasons not to way overbuild tubing systems too (cost, sap heating).

[DrTimPerkins]

But when the sap is running hard, the ladder works at near capacity and the lines fill up to near full height. At that point, the vacuum loss equals about 1" of mercury. As sap flow slows down, the average liquid level in the lines drops (by a lot) and more vacuum slips by. I have a ladder right next to my driveway with vacuum gauges at each side and I see this effect frequently.
Ken

Ken is exactly right. At peak flows, you will generally experience a drop in vacuum beyond the ladder due to the inability of air (CFM) to efficiently pass the fluid-filled section of pipe. Under low or no-flow conditions, vacuum might be relatively equal. Ladders are fine if needed, but best to avoid if you can.