16
Figure 8 Possible alignment technique
5.3
Filling the dewar
The Cryojet can be run continuously for as long as required. The dewar can be refilled
while the Cryojet is running.
Fit the liquid nitrogen hose from your supply dewar onto or into the fill tube. Make sure
it is held in place so that it will not be blown free by the pressure of nitrogen during the
fill. Use a low pressure in the supply dewar - preferably less than 1 bar. Open the valve on
the supply dewar slowly, as the sample flow temperature may be temporarily affected by
an increase in pressure in the dewar. Close the valve on the supply dewar slowly to stop
the fill.
5.4
Using the dipstick to measure the level of
liquid nitrogen
A dipstick (a long plastic rod) has been provided as a simple way of estimating the level of
liquid in the dewar. (A digital level meter and probe are also available - see separate
manual if these have been supplied.) Slowly lower the dipstick into the dewar through
the fill port until it hits the bottom, and wait a couple of seconds. Then pull it out, and
wait a few seconds for frost to form on the surface. The length of the frosted section is
the depth of liquid in the dewar. Do not touch the cold part of the dipstick with your
bare hands.
For depths between 10 cm and 80 cm, the dewar holds about 0.98 litres for every
additional centimetre of liquid. (See calibration chart below.) A flow of 1 litre/min of gas
corresponds to a consumption of 0.086 litre/hour of liquid, i.e. about 0.088 cm/hour. In
addition, there is a boiloff from the dewar of about 0.10 cm/hour
Centre nozzle in
this position
Withdraw nozzle to
this position for
diffraction studies
Sample
