For optimal transportation of your crystals it is imperative that you look after your dry shipping dewars. Here are some tips on how to make sure that you don't lose your crystals or introduce ice onto your pucks and pins.
Handling and loading
- Handle with care. Sudden impact can damage the dewar: please ship your dewars in the appropriate shipping container.
- Be careful when placing heavy items (puck holders for example) in the dewar. Do not drop them in, since this could damage the neck of the dewar.
- Do not pack items that are too tall for the dewar, nor incorrectly install its lid to make the items fit. Forcing the lid down can damage the neck
Charging with liquid nitrogen
- Charge the dewar as recommended in the manufacturer's instructions (photocopy these and tape to the side of the dewar if necessary), ensuring all residual liquid nitrogen is poured out of the dewar prior to shipment.
- Minimise liquid nitrogen spillage on the vacuum release valve near the top of the dewar.
- Check that the 'charged' dewar weight is in line with manufacturer's recommendations (e.g. in the case of the Taylor Wharton CX-100 dry shipper dewar, a charged dewar will weigh 3.6kg more than the 'dry' weight, and thus provide enough absorbed liquid nitrogen to keep the dewar at liquid nitrogen temperatures for 21 days, provided the vacuum has not been compromised).
- How do I check the dewar holds its charge?
- Properly charge the dewar as per manufacturer's instructions.
- Fill with liquid nitrogen and leave the dewar for 2-3 hours.
- Excessive accumulation of condensation or ice indicates damage.
- Measure liquid nitrogen level at 24 hour intervals.
- A decrease in level of 150mm indicates a damaged dewar.
- Check the dewar every time you use it (or at least every 3 months).
- Ensure the dewar is dried between uses. Residual moisture can cause damage to the foam material if frozen in situ.
- How do I speed up drying? What is the most effective procedure?
- Purge with dry nitrogen or air.
- Leave in a dehumidified room.
- Be careful: it may still take several days to fully dry.
- How do I know if it is dry?
- Weigh the dewar at time of purchase (record this on the dewar).
- When dry, the dewar should be within 0.5kg of the original dry weight.
- Weigh during drying until it no longer decreases.
- If you don't have time to dry the dewar properly between visits to synchrotrons, we strongly advise you to purchase more shipping dewars.
A well cared for dewar that is properly charged with liquid nitrogen before use should keep crystals safe for at least a week without refilling being required.