Quote Originally Posted by JoeJ View Post
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).