Well, my first instinct was to suggest putting two tanks in parallel,
but with further thought, that might not solve your problem.
If the flow capacity is insufficient, the pressure should drop to unacceptable
levels, analogous in some ways to drawing too much
current from a battery with internal resistance.
First check the ratings of the equipment to eliminate the possibility
of insufficient ratings:
MAS probes draw 2000 l/h (70.6 ft^3/h)
according to:
http://www.bruker-biospin.de/NMR/avance/vtu.html
Assuming you have the same type of tank that I use,
Dura-Cyl, rated tank output is 10,000 - 11,000 l/h
(350 to 400 ft^3/h) depending on the model.
To confirm, specs can be found:
http://www.chart-ind.com/pdf/duracyl.pdf
I'm sure that is not including losses from external tubing, regulators, etc.
but I'm sure 1/4" tubing or larger should be sufficient for this flow.
So ratings in theory are OK, flow rates are well within specs.
Also, since you're reading sufficient pressure, it doesn't seem that
the problem is tank flow capacity. Something must be happening
between your regulator and the probe.
Perhaps it is:
* blockage downstream of your regulator
perhaps the MAS unit has some internal filter or valve that became clogged?
* a control downstream which requires adjustment.
* malfunctioning MAS control unit
* some control parameter not set properly in software or firmware
Even though the boiloff from a cryogen tank is supposed to be very pure,
there could be material that makes its way from the external fittings.
Someone handling the tanks could get oil, dirt in the gas use outlet,
or perhaps it simply happens during transport. Even if you blow it
out before connecting to your system, stuff can take time to be cleared out.
>We have been trying some low temp MAS using N2 boiloff to provide
>clean dry N2 gas. Our N2 source is a standard 230 l high pressure
>(> 200 psi)
>dewar with the "pressure building" valve. The problem is, even with
>the pressure
>building valve fully open, we can't get enough flow for the bearing,
>drive, purge, and
>VT requirements (pressure is fine). We just can't evaporate the N2
>fast enough.
--
Please note that the opinions expressed here are entirely my own and
does not necessarily reflect those of Memorial Sloan-Kettering Cancer Center
(For The Best Cancer Care. Anywhere. http://www.mskcc.org)
George D. Sukenick, Ph.D.
Assistant Laboratory Member & Manager of the
Nuclear Magnetic Resonance Analytical Core Facility
supporting drug discovery synthetic organic chemistry at
Sloan-Kettering Institute for Cancer Research
Received on Wed Oct 27 2004 - 13:47:22 MST