Xylem H-312-22 - Manual (Page 17)

Chapter 3
Maintenance
H-312
Maintenance 3-1
Figure 8 Dry Air Junction Box
3.1 Maintenance
Sustained operation of the H-312 pressure sensor is almost maintenance-free. Experience has
shown that moisture condensing in the atmospheric reference tube creates the largest percentage
of field problems. The desiccant in the H-312 junction box dry air system should be changed on a
fixed schedule, normally every three to six months. Different areas in the world have widely
varying humidity and temperature fluctuations. Pay close attention to the desiccant condition in
your particular installation. The desiccant packs contain indicating silica gel and have a
transparent window that allows the condition of the desiccant to be observed. The silica gel has a
blue color when dry and changes to pink as it absorbs moisture.
3.2 Changing the Desiccant
The desiccant in the H-312 junction box dry air system is easy to change.
Step 1 Remove the clear plastic lid.
Step 2 Replace the desiccant packs
Step 4 Reinstall the clear plastic lid.
Precautions
Make certain the seals in the
liquid tight cable fittings on the
dry air junction box are tight.
Make certain the dry air junction box lid is screwed on and sealed properly.
Make certain the screened vent port on the lid of the dry air junction box is not covered or
blocked.
3.3 Maintaining Desiccant Packs
The desiccant bags have a transparent strip which allows the condition of the desiccant to be
visually checked. The desiccant has a dark blue color when dry and changes to pink as it absorbs
moisture. The desiccant packs can be reused by drying them in an oven at 180 F to 220 F for 4
to 8 hours or until the desiccant returns to a dark blue color.