APPLICATION NOTE NO. 71
Desiccant Use and Regeneration (drying)
Revised March 2008
Print version
This
application note applies to all Sea-Bird instruments intended for underwater
use. The application note covers:
- When
to replace desiccant
- Storage
and handling of desiccant
- Regeneration
(drying) of desiccant
- Material
Safety Data Sheet (MSDS) for desiccant
When to Replace Desiccant Bags
Before
delivery of the instrument, a desiccant package is placed in the housing, and
the electronics chamber is filled with dry Argon. These measures help prevent
condensation. To ensure proper functioning:
-
Install
a new desiccant bag each time you open the housing and expose the
electronics.
-
If
possible, dry gas backfill each time you open the housing and expose the
electronics. If you cannot, wait at least 24 hours before redeploying, to
allow the desiccant to remove any moisture from the chamber.
What
do we mean by expose the electronics?
- For most battery-powered Sea-Bird instruments (such as SBE 16,
16plus, 16plus
V2,
16plus-IM,
16plus-IM V2, 17plus,
19, 19plus, 19plus V2, 25, 26,
26plus, 37-SM,
37-SMP, 37-IM,
37-IMP, 44,
53,
54,
55,
Auto Fire Module
[AFM]), there is a bulkhead between the battery and electronics
compartments.
Battery
replacement does not affect desiccation of the electronics, as the batteries
are removed without removing the electronics and no significant gas exchange
is possible through the bulkhead. Therefore, opening the battery compartment
to replace the batteries does not expose the electronics; you do not need to
install a new desiccant bag in the electronics compartment each time you
open the battery compartment. For these instruments, install a new desiccant
bag if you open the electronics compartment to access the printed circuit
boards.
- For the SBE 39,
39-IM, and 48,
the electronics must be removed or exposed to access the battery. Therefore,
install a new desiccant bag each time you open the housing to replace a
battery.
Storage and
Handling
Testing
by Süd-Chemie (desiccant’s manufacturer) at 60% relative humidity and 30 °C
shows that approximately 25% of the desiccant’s adsorbing capacity is used up
after only 1 hour of exposure to a constantly replenished supply of moisture in
the air. In other words, if you take a bag out of a container and leave it out
on a workbench for 1 hour, one-fourth of its capacity is gone before you ever
install it in the instrument. Therefore:
- Keep
desiccant bags in a tightly sealed, impermeable container until you
are ready to use them. Open the container, remove a bag, and quickly
close the container again.
- Once
you remove the bag(s) from the sealed container, rapidly install the
bag(s) in the instrument housing and close the housing.
Do not use the desiccant
bag(s) if exposed to air for more than a total of 30 minutes.
|
|
Regeneration
(drying) of Desiccant
Replacement desiccant bags are available from Sea-Bird:
- PN
60039 is a metal can containing 25 1-gram desiccant bags and 1 humidity
indicator card. The 1-gram bags are used in our smaller diameter housings,
such as the SBE 3 (plus,
F, and S),
4 (M and C),
5T and 5P, 37 (-SI,
-SIP,
-SM,
-SMP, -IM,
and -IMP),
38, 39,
39-IM,
43, 44,
45, 48,
49, and 50.
- PN
31180 is a 1/3-ounce desiccant bag, used in our SBE 16plus, 16plus
V2,
16plus-IM,
16plus-IM V2,
19plus, 19plus V2,
21, and
52-MP.
- PN
30051 is a 1-ounce desiccant bag. The 1-ounce bags are used in our larger
diameter housings, such as the SBE 9plus,
16, 17plus,
19, 25,
26,
26plus, 32,
53 BPR,
54,
55,
AFM,
and PDIM.
However,
if you run out of bags, you can regenerate your existing bags using the
following procedure provided by the manufacturer (Süd-Chemie Performance
Packaging, a Division of United Catalysts, Inc.):
MIL-D-3464
Desiccant Regeneration Procedure
Regeneration
of the United Desiccants’ Tyvek Desi Pak® or Sorb-It®
bags or United Desiccants’X-Crepe Desi Pak® or Sorb-It®
bags can be accomplished by the following method:
- Arrange
the bags on a wire tray in a single layer to allow for adequate air flow
around the bags during the drying process. The oven’s inside temperature
should be room or ambient temperature (25 – 29.4 °C [77 – 85 °F] ). A
convection, circulating, forced-air type oven is recommended for this
regeneration process. Seal failures may occur if any other type of heating
unit or appliance is used.
- When
placed in forced air, circulating air, or convection oven, allow a minimum
of 3.8 to 5.1 cm (1.5 to 2.0 inches) of air space between the top of the
bags and the next metal tray above the bags. If placed in a radiating
exposed infrared-element type oven, shield the bags from direct exposure to
the heating element, giving the closest bags a minimum of 40.6 cm (16
inches) clearance from the heat shield. Excessive surface film temperature
due to infrared radiation will cause the Tyvek material to melt and/or the
seals to fail. Seal failure may also occur if the temperature is allowed to
increase rapidly. This is due to the fact that the water vapor is not given
sufficient time to diffuse through the Tyvek material, thus creating
internal pressure within the bag, resulting in a seal rupture. Temperature
should not increase faster than 0.14 to 0.28 °C (0.25 to 0.50 °F) per
minute.
- Set
the temperature of the oven to 118.3 °C (245 °F), and allow the bags of
desiccant to reach equilibrium temperature. WARNING:
Tyvek has a melt temperature of 121.1 – 126.7 °C (250 – 260 °F) (Non
MIL-D-3464E activation or reactivation of both silica gel and Bentonite clay
can be achieved at temperatures of 104.4 °C [220 °F]).
- Desiccant
bags should be allowed to remain in the oven at the assigned temperature for
24 hours. At the end of the time period, the bags should be immediately
removed and placed in a desiccator jar or dry (0% relative humidity)
airtight container for cooling. If this procedure is not followed precisely,
any water vapor driven off during reactivation may be re-adsorbed during
cooling and/or handling.
- After
the bags of desiccant have been allowed to cool in an airtight desiccator,
they may be removed and placed in either an appropriate type polyliner
tightly sealed to prevent moisture adsorption, or a container that prevents
moisture from coming into contact with the regenerated desiccant.
NOTE:
Use
only a metal or glass container with a tight fitting metal or glass lid to store
the regenerated desiccant. Keep the container lid closed
tightly to preserve adsorption properties of the desiccant.
Material
Safety Data Sheet (MSDS)
Last modified:
14 Oct 2010
Sea-Bird Home Phone: (+1) 425-643-9866
Fax: (+1) 425-643-9954 E-mail:
seabird@seabird.com