MVE Biological Systems
TEC 3000 Operating and Maintenance Freezer Manual
13289499 Rev H •
114
9.2. Preventative Maintenance Procedures
Level Verification
The differential pressure measurement system used on MVE freezers is nearly maintenance free.
It provides a high level of accuracy and resolution to give the operator a precise indication of the
exact amount of LN2 present in the freezer at all times. Despite its reliability, it is important that the
accuracy of the level measurement system is verified on a weekly basis. This will prevent a control
system malfunction from adversely affecting the temperature in the freezer storage space. Use the
meter dipstick provided with every MVE freezer to manually measure the amount of LN2 in the
freezer. Follow the “Dip Stick Procedure” listed in section 6.3.2 to properly measure the level. If the
level is off by 1.0 inch (25mm) or more, follow the calibration procedure listed in the
aforementioned section.
Verify Adequate Supply
Adequate LN2 supply pressure and flow is imperative to the proper operation of MVE freezers.
Any LN2 supply whether from bulk tank or liquid cylinder must be able to maintain a pressure of
22-35 psi (1.52
– 2.41 bar) during a filling cycle, and must have enough liquid to ensure the
completion of a fill cycle. The majority of nuisance alarms reported from MVE freezers are due to
inadequate supply.
1. Observe the pressure of the supply source. Ideally, pressure should be 22
– 35 psi (1.52 –
2.41 bars).
NOTE: It is very common for the pressure gauge on an industrial liquid cylinder to be
inoperative. If you suspect this to be the case, install a pressure gauge inline between the
liquid cylinder and the freezer for verification
2. Verify the amount of liquid in the supply source. Most bulk tanks have some method of
digital or analog volume measurement. Liquid cylinders typically use a sight gauge. As with
the pressure gauge on liquid cylinders, it is common for the sight gauge to be inoperative.
3. The minimum amount of liquid necessary in the supply should be enough to completely fill
the number of freezers it is supplying. This amount can be determined from the LN2 inch
to volume table in the Appendix.
4. Initiate a fill start on at least one freezer on the network. The supply system should be able
to maintain appropriate pressure throughout the duration of the fill cycle.
5. If the supply is determined to be inadequate, have your gas supplier replenish/replace
the supply.
