Teledyne 4220 - Manual (Page 136)

4220 Flow Meter
Section 6 Maintenance and Service
6-2
6.2 Reactivation of the
Desiccators
The 4220 has a reusable desiccant canister held by a steel clamp
on the inside of the case lid. There is also a tubular desiccant car-
tridge on the top of the case next to the connectors. The canister
contains silica gel that adsorbs moisture trapped inside the flow
meter's case when it is closed. This keeps the inside of the case
completely dry during shipment, storage and use. If you leave
the case open, the desiccant will quickly absorb moisture from
the surrounding air and will soon be saturated. It will no longer
be able to protect the flow meter. Both desiccators use a color
indicator that changes from blue to pink or from yellow to green
when saturated. The external desiccant cartridge vents the ref-
erence port of the pressure transducer.
6.2.1 Regenerating the
Internal Case
Desiccant
Look at the desiccant canister each time you open the case. The
canister has a window on its side that appears blue or yellow
when the desiccant is dry. As the desiccant absorbs moisture, the
window will turn pale pink or green. When the window is pink or
green, you need to regenerate the desiccant, or replace it with the
spare canister provided in the flow meter accessory package.
Remove the canister from the flow meter by pulling outward on
the spring clamp, releasing its hold on the canister.
Remove the canister and heat it in a vented oven in a well-venti-
lated room at 300°F (150°C) for about three hours, or until the
blue color returns. Do not use a microwave oven; the metal case
of the canister could cause arcing. After cooling, reinstall the can-
ister in the flow meter. Make sure the window on the side of the
canister remains visible.
Figure 6-1 Location of the Desiccant Canister