Reactivation Of The Desiccators; When To Recharge The Desiccant In The Tubes - Teledyne 4250 Installation And Operation Manual

4250 Flow Meter
Section 5 Maintenance and Service
5.2 Reactivation of the
Desiccators
5.2.1 When to Recharge the
Desiccant in the Tubes
5-2
The 4250 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 indi-
cator that changes from blue to pink, or yellow to green, when
saturated. The external desiccant cartridge vents the reference
port of the pressure transducer.
Both the 4250 and the optional Quick Disconnect Box dry the
probe's vent tube with a desiccant tube. Inspect the desiccant
tube frequently. Exposed to humid air constantly, the desiccant
will become saturated quickly. If the desiccant is unable to dry
the vent tube and the tube becomes blocked with moisture, the
level readings will be unreliable, and the probe can suffer per-
manent internal damage.
Teledyne Isco uses silica gel (SiO
canisters:
• One looks like small beads or pellets that are blue-black
when dry, pale pink to transparent when saturated.
• The other looks like coarse sand, yellow when dry, dark
green when saturated.
Regenerate silica gel before all the desiccant in the tube turns
pink or green by heating.
Another type of desiccant may be used in the tubes: anhydrous
calcium sulfate (CaSO
4
of tinted plaster and changes from blue when dry to rose-red
when saturated. Regenerate the calcium sulfate desiccant before
all the desiccant in the tube turns rose-red. Do not put calcium
sulfate in the metal desiccant cartridge.
The filters in the ends of the desiccant tube prevent desiccant
particles from entering the vent line. When they become soiled,
replace them with cotton balls.
The desiccant in the tube requires periodic recharging to dry it
after it becomes saturated with moisture. After repeated
recharging, it eventually requires replacement.
Note
Both desiccants, anhydrous calcium sulfate and silica gel, are
regenerated in the same way but require different tempera-
tures. Calcium sulfate requires temperatures of 400° to 450° F;
silica gel requires temperatures of 212° to 350° F.
Either chemical may produce irritating fumes when heated.
See Appendix D Material Safety Data Sheets for silica gel des-
iccant information.
To regenerate all desiccators safely, follow these guidelines:
Always use a vented, circulating forced air convection oven in a
) in the desiccant tubes and
2
). Calcium sulfate looks like rough chips