SPI-DRY™ Critical Point Dryers
Special comments for those working with aerogels and MEMS systems
Seals in critical point dryers do not last forever. The challenge is to
make them last longer rather than shorter lifetimes, both because of the
cost of changing seals but also the downtime and labor cost to make the
change.
For many years, life science users were always instructed to flush out
their solvents after each use and under no circumstances, allow residual
solvents to remain in the unit which can have the effect of leaching out
or even dissolving away components of either the "o" rings or from the
plastic bonded seals. Premature "o" failure is almost always the result
of inadequate flushing after each use of the unit.
With the advent of large scale use of the SPI-DRY Critical Point Dryers
for applications in both aerogels and MEMs, both kinds of samples
employing sometimes highly aggressive solvents, for example, methyl
alcohol, we have seen a shortening of the life times of some of the
seals. So our first recommendation is to redouble all efforts at
cleaning the unit after use.
And the second recommendation is to use our special "chemical
resistant" replacement "o" rings,
nothing is of course forever, but in use situations where certain solvents, such as
acetone or MEK are being used, we do recommend the
replacement parts be of EPDM construction, rather than the nitrile construction.
If ethanol is being used, there there is no difference, and nitrile rubber will be
just as good as EPDM.
On the subject of seals, the seal that is normally affected, that is,
the one that will fail the fastest and therefore most frequently, is
the front 1" diameter window seal. One should note that this is the
same size seal for either the regular or jumbo size units. For
the other seal, the one sometimes called the window seal,
remember that the two units have two different size seals.
However, this seal fails very rarely in comparison with the other one.
But do remember that the main reason for seal leakage and eventually seal
failure is inadequate flushing.
We have heard tales of some innovative and wise Professors who allowed
their students to have a contest, to see who could make the loudest noise
during the flushing step. The students were very competitive and in the
process, they all did excellent cleaning, and consequently, they had almost
no seal failures! Of course this might not work in all cases since because
some samples could not stand such turbulent treatment, but that wise
professor always recommended the use of the
SPI Microporous Specimen
Capsules and that seemed to be more than enough protection to keep fragile
specimens from becoming damaged.
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Monday December 01, 2008
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