Strictly speaking the Charles Austen pumps are not 'liquid nitrogen' pumps.
They are merely diaphragm vacuum pumps. When in use on the
VG/Micromass/Europa cold finger systems they are placed down stream of the
cold finger. Switching on the pump evacuates the cold finger and liquid
nitrogen is pumped by the pressure difference between the vacuum and the
1atm head space above the liquid nitrogen in the dewar.

We have used similar arrangements in cold finger assemblies and have had to
be careful that the diaphragm does not cool to too low a temperature. If it
does so it becomes rigid and the pump stops working.

The address for Charles Austen is:

Charles Austen pumps Ltd.,
Royston Road,
Byfleet,
West Byfleet,
SURREY KT14 7NY,
U.K.

Tel: 01932 355277 (use appropriate intnl. dialing codes)
Fax: 01932 351285

I'm not sure if they have a web or email address.

Of course any other diaphragm pump with similar capacities will do the same
job.

It is much more difficult to actually pump liquid nitrogen. There are
commercially available motorised pumps, pressurised dewars and cryogenically
rated solenoid valves for switching the flow of liquid nitrogen. However
these systems can be expensive and often a little inflexible, particularly
where you need to have a regulated flow of liquid nitrogen to several small
glass dewars all supplied from a single large dewar.

We have a system operating in our laboratory in which we use a 50L dewar to
supply liquid nitrogen to up to 3 small glass dewars (ca. 2L) and maintain
levels over extended operating periods (24 hours plus). In practice more
than 3 dewars can be filled and the device will continue to operate whilst
the 50L dewar is topped up. The sytem doesn't rely on any moving pumps, or
the need to use cryogenically rated solenoid valves and pressurised liquid
nitrogen dewars. We use simple solid state level detection in the glass
dewars to switch on and off the liquid nitrogen pumping. The complete device
can be built for a matter of say $100.

We've submitted a note to Reviews of Scientific Instruments, but I'm more
than happy to send copies of the manuscript to anyone who is interested.

Just email me directly and I'll make sure a copy is forwarded.

Good luck everyone,

Paul Dennis
Stable Isotope Laboratory,
ENV,
UEA,
NORWICH NR4 7TJ