27
TROUBLESHOOTING
9.1 FREQUENTLY ASKED QUESTIONS
Why has the freeze dryer been
running for over 46 hours and the
process is not complete?
There are a number of factors that
can contribute to longer cycle
times. Some of which may be a
combination of the following:
1.
Some foods are more challenging
to freeze dry than others. Because of
their cellular structure and moisture
content, oranges, pineapple,
strawberries, blueberries, and other
foods/meals with high amounts of
liquid will take longer to freeze dry.
The freeze dryer is measuring the
moisture content and knows when
the process is complete.
2.
There is so much water in the
food that the condensed ice ring has
begun to form on the trays. While
rare, if this occurs, the freeze dryer
will not be able to recognize that
the process is complete because it
will sublimate the ice that is coming
onto the trays. In a situation like
this, it would not be able to verify
that all of the moisture is removed
because of all the ice. If this
happens, simply remove the trays
and put them in the freezer, defrost
the ice in the freeze dryer, put the
food back in the freeze dryer, and
allow it to finish the process. Again,
this is very rare.
3.
Your vacuum pump oil needs
to be changed. As the oil in your
vacuum pump gets older, the cycle
time for the foods will increase. If
the oil in your vacuum pump needs
to be changed, a batch of food that
would normally take 24 hours to
complete, could take 46 hours to
complete. Consider a vacuum pump
power flush (
see page 24
).
4.
The freeze dryer is working
properly if during the vacuum
pump/drying portion of the freeze
dry cycle, the vacuum is reading
between 400-800 mTorr. If the
reading is consistently above 800
mTorr, it is likely time to change
your vacuum pump oil, check for
leaks, or clean your vacuum pump.
How do I extend the life of my
vacuum pump oil?
As your vacuum pump runs, small
amounts of water will trickle into
the vacuum pump. In order to drain
any water that has accumulated,
once you are ready to begin a new
batch of food, open the oil drain
valve on the vacuum pump. When
you do this, you should also drain a
small amount (approx. 1 tablespoon)
of the used oil, as well. Close the
drain valve and add a small amount
of new vacuum pump oil into the
vacuum pump. This will replace
the oil that was drained and will
