Tap count on 3/4" mainline

[Polaris1]

I'm new to this site and new to vacuum. 1 of the big manufacturers say 3/4 mainline is good for 250 taps. But at what length of mainline. If u have 1000ft of line would it increase tap count?

[JoeJ]

3/4" will handle 250 taps and the length of the line does matter. The longer the length of the line, the more the vacuum goes down at the far end. With a 15 cfm pump 3/4" is good for 259 taps and 4 cfm at 1,000'. Using the same 15 cfm pump with 1" pipe, the taps are 513 and 7 cfm at 1,000'. If I were you, knowing what I know now, I would install only 1" pipe. (When you install either the 3/4" or 1"pipe, install a tension grip on each end of the line.) It does not cost that much more and the 1" will handle a lot more taps. If you are like most people who start sugaring, you will end up with a lot more taps than you planned on and then the 3/4"line limits you

Joe

[DrTimPerkins]

Joe is spot on. Go with the 1" pipe. It is far more forgiving as well. You are always aiming to have AT MOST 1/2 of the pipe full of liquid during peak flows. That is under ideal installation conditions. Now consider having a 1/4" sag in the mainline.

3/4" pipe half-filled gives you 0.375" of air space across the top during peak flow. A 1/4" sag will remove 0.25" of that, leaving you with 0.125" of space at the top to move air, and a fairly small cross-sectional area. That is before you factor in turbulence.

A 1" pipe will give you 0.5" of air space at the top, and 0.25" when you factor in a 1/4" sag. The cross-sectional area for air transfer is far higher in this case.

How many people can install and maintain a mainline with a 1/4" tolerance for sags?

So why not go with huge mainlines? Two reasons: cost and unacceptable levels of heating of sap during low/moderate flows.

[jrgagne99]

Dr. Tim,
If I understand correctly, this is the reason for running two lines- one to transfer the vacuum and one to move the sap. Have there been any studies that quantify, say under average-run conditions, how much vacuum is lost for each sag that completely fills the mainline? I've always heard that sags are bad, but have never seen exactly how bad is bad.
Thanks.

[DrTimPerkins]

You are correct. What I was describing was the situation with a single mainline system. Conditions are different for a dual (wet-dry) mainline system. For at least the wet-dry component of that system, the transfer efficiency of sap and air is very high.

I don't know of any good studies focusing solely on sags in a maple tubing system (to equate the # of sags to vacuum loss), but there are a lot of engineering studies on flow in pipes that are applicable in some ways. Our system is a bit different in that we have both liquid and air (often at very low pressures = vacuum), both of which move in the pipe, but at vastly different rates (air will move WAY faster than liquid if allowed to). What further complicates matters in maple is that we have freezes in the system, sags (because pipe is not always linear), slope changes, turbulence at fittings, leaks, tree gases (acting as porous air injectors), varying vacuum levels (which impacts the volume of air), etc. So it is immensely hard to generalize. However, it is well understood that sags will generate what is termed "slug" or "plug" flow, which are some of the least efficient ways to transfer liquid and is also a very poor way to maintain good air movement. Removal of air (to maintain the best vacuum level) is greatly impeded under such conditions.

CFM is what moves the air from the system, but vacuum level is what creates the pressure differential between the tubing system and the tree. Thus both are important. If you have good tight and straight lines, size and installed appropriately, and maintained as leak free as possible, there is more CFM available to move out the air (from tree gases) to maintain the vacuum level to achieve high yields. This is the situation for mainlines....lateral lines (5/16" and 3/16") are somewhat different.

So I really don't have an answer for you, however...the effects of sags are cumulative, meaning that the more sags you have the lower the efficiency and the more CFM it'll take to remove the air and maintain a steady vacuum level. A few sags might not be a big deal...a lot of saps certainly is. It all goes back to that energy conversation in another tread...pushing or pulling slugs of sap or air up and down hills takes a lot more energy (CFM) than running steadily down a hill. Tight -- straight -- downhill.

We know that wet-dry mainline systems are associated (correlation) with about a 10% improvement in sap yield. This is at least partly due to the wet-dry system, but may also include other factors as well. Keep in mind that only part of the entire mainline/tubing system is separated into wet-dry. Spur mainlines off the wet-dry (through a manifold) are essentially single pipe systems.
Finally, we know that if we extend the wet-dry concept from the pump all the way to the tree through the lateral line system, we get another 10%+ increase in sap yield. The problem with that approach....it is not economical to do at the current (U.S.) bulk price of syrup. If bulk syrup were close to or above $3.00/lb it starts to make sense.

For fun, take a look at: https://www.youtube.com/watch?v=pkhVxqDg_fk and https://www.youtube.com/watch?v=iiV4H1OFO6Y

[log cabin luke]

Hi Dr.Tim

Could you point me in the direction of any studies done on the capacity of a 3/4 " main line that is vented with 3/16 tubing on natural vac running into it. If no studies have been done like I suspect How much of an effect do you think the venting will have on the capacity of the line. The most that I have heard anyone putting on a 3/4 inch main is 1200 taps at a 10 % slope. I do not know if it was vented. When trying to maximize capacity of a main line what do you think would be the Ideal slope.


Thanks Luke

[DrTimPerkins]

Closest you're going to get is the NYS Maple Tubing Notebook (Steve Childs - Cornell Univ). Mainline generally shouldn't need to be vented (and lateral line almost never should be)...so there isn't going to be much of any research on that approach it in the maple world (perhaps for other industries). In this case you're only concerned with liquid flow out...the only air entering is to drain the pipe (to take the place of the sap). If you do vent, put a check valve at the top (air can enter...sap can't get out). As long as the line is graded and supported properly, no sags, no abrupt changes in slope or direction, it should be OK. If you're concerned about max flow capacity, go to 1" mainline...the price difference is fairly small.