3-2
180 liter LN2 Supply Tank
Thermo Scientific
Section 3
Theory of Operation
Filling Procedures
The following recommendations should be used to optimize liquid cylinder
filling:
* Keep the transfer lines as short as possible. Long uninsulated transfer
lines will result in higher fill losses and longer fill times.
* Any time liquid can be entrapped in a line between two valves, the line
must be equipped with a safety relief device.
* Conduct the filling operation in as short a time as possible.
* Do not overfill; fill only to the weight allowable by specification.
* Use minimum number of bends, valves and reducers.
* Use as large a transfer line as possible; at least 1/2" ID.
MVE recommends the "Lo-Loss" system for liquid cylinder filling. For
information ask for Form 2072 on the "Lo-Loss" from MVE.
The liquid cylinder should be visually inspected before every fill for
possible damage, cleanliness and suitability for its intended gas service. If
damage is detected (e.g. serious dents, loose fittings, etc.), remove it from
service and repair the unit as soon as possible.
All MVE liquid cylinders are tested for performance with low-purity liquid
nitrogen. For this reason, liquid cylinders intended for use in another
service should be thoroughly purged with the applicable gas prior to filling.
When filling a liquid cylinder with a cryogenic liquid, the transfer may be
made with a centrifugal pump or through a pressure transfer operation.
Liquid will always flow from a
vessel of higher pressure to
one with low pressure. This
method is commonly used to
fill liquid cylinders by
connecting a transfer line
between the delivery source
and the Fill/Liquid valve of
the liquid cylinder. The
transfer takes place as the vent
valve of the liquid cylinder is
opened. This allows gas to
escape and lowers the pressure
in the liquid cylinder. This
method should always be used
for liquid only vessels such as
the Cryo-Cyl LP. Figure D
shows the pressure transfer
method of filling.
Pressure Transfer
VAPORIZER
PRESSURE
BUILDING
COIL
LIQUID
IN
GAS
OUT
GAS
Liquid
Figure D.
Pressure Transfer
