Zero Bulk Tanks and Inches of Vac.

[findandy]

I've been using Zero tanks for four yrs without a problem. My pumps have been Surge milking machine pumps. According to "my" Guage my max. Vac has been 21-22". As I think about upgrading to a pump designed for maple I'm getting a little nervious. I understand tank failures have happened. Is there a safe limit to what these tanks will handle.

[Teuchtar]

Several of us have been using Zero vacuum tanks for a while. If you consider that the tanks are designed to go into a milking system at 15"Hg Vac (at the claw), then the number you give is significantly higher than the intended design load.
Most people exchanging info on this site wouldn't venture above the vacuum you give.
But if you want to go higher (for experimental purposes) please take note of the exact vacuum level at which the tank collapses, and share that with us.

A really couragous experimenter might run a test as follows:

Fill the tank completely full with water. ( so it won't violently collapse during this experiment)
Disconnect it from the pipeline, so as to not have any volume of vacuum.
Use a factory calibrated vacuum gauge.
Multiple gauges would be even better to minimize the gauge error. (average the reading)
Connect a good quality vacuum regulator that will predictably and repeatable manage vac.
Rig up a dial indicator to read the gap across the manhole with its cover applied. I think youd probably need to epoxy little blocks on the tank, with a countersink to take the dialgauge.
Draw down the vacuum and read the gap. Read the vac and deflection at 2" increments
Draw the curve of gap versus vac all the way from 0 to 22 and back to 0.
Take data up and down the vacuum several times to be sure your reading is repeatable.
Every vacuum excursion should come back to zero with the same trajectory.
Next: the couragous part - increase the vacuum 1/2" to 22-1/2 and return to zero.
Map these new gap vs vac points on the same curve.
Now you're walking the plank blindfolded.
(but at least youve made a map to get back home)

Data interpretation:
If the gap (at zero vac) goes back to its original reading, then you haven't caused yielding.
If you do get any zero-offset, then that means you've permanently yielded the structure.
Also if the curve changes shape at the higher levels, thats bad too. Don't go further.
But if the gap always goes back to zero, you should be able to take the next step of 1/2"
Don't go any further than onset of yield. ( No way go more than 0.020" would be my guess)

Next: Plot the curve and tell us all what you get.

Hope you do this test and tell us because I'm chicken to do it on my own tank.