6875 Freezer/Mill
Page 27 of 42 SPEX® SamplePrep LLC DEC 2015
7.0 6820 AUTO-FILL SYSTEM
7.1 Description
The 6820 Auto-Fill System automatically transfers liquid nitrogen (LN) to the 6875 Freezer/Mill
during operation, making hand-filling unnecessary. The Auto-Fill mechanism includes a cryogenic
valve linked to LN sensors in the tub. When the LN level is low, the valve opens during Precool or
cooling stages to let LN into the tub. The Auto-Fill System as supplied also includes a safety valve
for the LN transfer hose.
LN transfer hoses can vary with the LN supply tank or line and are therefore not included with the
6820 Auto-Fill System. Four-foot and six-foot transfer hoses of standard design (part numbers
6906 and 6907) can be purchased from SPEX SamplePrep, or custom transfer hoses can be
designed and supplied by the user. The LN inlet is a male ½ inch JIC fitting placed low on the right
side of the Freezer/Mill, so the outlet of the hose requires a female CGA295 fitting. The 160 liter
and 240 liter LN tanks used by many of our customers generally have a male 3/8 inch (9.5 mm)
NPT outlet, so SPEX transfer hoses come with a matching female 3/8 inch NPT fitting. Excessively
long transfer hoses are not recommended.
LN tanks come in two types, high-pressure and low-pressure. Some LN tanks have valve systems
to switch from low pressure to high pressure. Always use a low-pressure LN supply, with a
delivery pressure of 20-22 psi.
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