Mystery Vacuum leak?

[I Luv Stainless]

Yesterday it was 35 degrees and the sap is just dribbling, so I was checking vacuum quality in the sugarbush. I have 4, 1” mainlines feeding my releaser in the saphouse where I am pulling 22” hg. The vacuum exhaust was pushing very little air, so I knew I did not have any major leaks, I took care of those last week.

However, the taps of just one mainline had very little suction. So little that the suction at the tap would not hold itself against your finger, I’m guessing it was pulling 5-10 hg. (I need to make a gauge so I have exact numbers). This was true on taps near the saphouse and those 200’ away. All ice appeared to be out of the mainline, I did correct a few spots with questionable pitch but it was above freezing and any ice should have cleared itself. As I write this I’m thinking could it be the 1” pvc valve at the releaser?

My Question: How do you chase down mainline blockage problems? Any tips would be welcome.

[madmapler]

Maybe diconnect at the first saddle and check it then work your way back.

[BreezyHill]

This season has showed me several odd abnormalities.

A few things to remember. Where you have a leak you can freeze sap when temps are just above freezing.
Slush in a vacuum system will lodge and pack as hard as regular ice.
Valves that are not full port will be an issue down the road.

So...you did a great job of investigating and you have likely pointed to the fault.

The valve is the likely villain. I suspect that you have slush that has blocked the valve and the plastic is taking longer to warm up. In the future the use of the next size larger valve than the main line with step fittings will eliminate this potential bottle neck. For now a hair drier on the sight will warm the fitting to dislodge the ice. Careful use of a torch on low setting will also do the trick...but be careful to not damage the valve with high heat.

I had this same scenario with a quick disconnect this season and pulled apart the quick lock to find slush blockage. Chipped it out put it back and it did it again not 5 seconds after reconnecting. The second time it kept flowing. Warming would have been better but the heat gun was used in the barn on a calf earlier that day.

Good Luck!

Ben

[boron1034]

On days that are just above freezing I have found that the airflow from large leaks, such as an open 5/16" line, will cause the sap in the mainline to freeze and block the line. I have found that it can even block it at the saddle where the leak is, causing everything farther up the main to have little or no vacuum. If I stand there long enough usually it will thaw out (especially if it is sunny) and I can hear the leak again, but at the right temp it will freeze up again quickly. It could be possible that you have a large leak somewhere on that line that you couldn't find because of the blockage.