Troubleshooting; Loss Of Vacuum - Thermo Scientific 8120 Operating And Maintenance Manual

Troubleshooting

Section 5
The troubleshooting section of this manual deals with the normal
operating conditions and the problems that may occur with the Cryo-Cyl
Series liquid cylinders. The troubleshooting guide assumes that the tank is
in its normal operating environment having a cooled down inner vessel
and a reasonable vacuum. Before troubleshooting an operational problem,
the liquid cylinder should be examined for vacuum.

Loss of Vacuum

The loss of vacuum on a liquid cylinder is usually associated with excessive
cylinder frosting or rapid pressure rise. Excessive pressure rise, however, can
be normal. A new liquid cylinder or one that has not been used recently is
considered to have a warm inner vessel. Warm cylinders will build pressure
fast after filling and vent off the excess. A liquid cylinder that has been
filled and not used will build pressure and vent the excess off. The higher
the pressure was in the storage tank at the time of filling, the faster the
liquid cylinder will vent off.
Excessive pressure rise can also be an indication of vacuum loss. The Cryo-
Cyl Series liquid cylinders are equipped with a outer jacket rupture disc
that will reverse and tear if there is a loss of vacuum. The rupture disc is
protected from the environment and tampering by a metal "Warranty
Seal". DO NOT REMOVE the metal warranty seal. If the rupture disc has
blown, the warranty seal will pop off. The rupture of the disc indicates an
inner vessel leak. Return the liquid cylinder to the factory for repair. If the
rupture disc is intact and a vacuum loss is still suspected, perform an
evaporative loss rate test.
Thermo Scientific 180 liter LN2 Supply Tank 5-1