Surge bulk tanks

[Thatcher12]

Are any Surge bulk tanks capable of holding a high volume of vacuum. If so, how can you tell than apart (certain serial numbers or models). Thanks

[maple flats]

Surge tanks, if the vacuum type, can hold a large volume of vacuum, but not a high level of vacuum. Vac type surge tanks are limited to 20", if in perfect condition, less if the inner tank has been compromised by dents or corrosion. The volume is related to the cubic feet of space above the sap.

[Thatcher12]

So no Surge bulk tanks are made to hold more then 20 inches of vacuum?

[maple flats]

Technically they are made to hold 15", that is what Dairy uses. If they are vacuum tanks they are tested to 20" when new. Beware, not all Surge tanks are Vacuum. I've been told they are labeled on one end, but I could never find this label on mine. I took the chance and ran mine at 18", successfully. Some on here were not as lucky. Tanks have imploded for them.