I've been making syrup every year since 2003, before that I made it some years just for family use. Last year was my lowest sap yield ever, sap amount was down slightly and everything was on vacuum (19" on one bush and 24" on another bush). Then my sugar % was the lowest ever. My sugar % for the total season was only 1.25% and my highest for any one day was 1.8%.
Sap yield, especially on gravity is extremely variable, but 10-20 gal per tap is very common. While seasons are not the same season after season, there are a few things you can do to get the best you can. Tap a little before the first sap run (watch the weather), use a new tap (and new drop every 3 years if using tubing), use a genuine tapping bit, not any old bit, not even a new hardware store bit, tapping bits ARE different. (then never use the tapping bit to drill anything other than tapping maples). The next thing to increase yield involves vacuum. Do you have any slope to help? Even if just 10-12' using 3/16 tubing can help but only if you can get at least 10 or more taps on a line (Ideal is about 25-30, max is somewhere between 35 and 40 something). Another thing is to add a vacuum pump. Many small operations get a nice boost using a diaphragm pump.
Then it's possible you could get more this year than last with just a good tapping bit and a new tap (or is a metal tap, boil it to sanitize it). Practice good tapping technique, drill in 1.5-2" max, don't wobble the drill and ton't pound the tap in, just gently "tap" it in.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.