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Essential Desiccant Breathers

Watchdog® Desiccant Breathers are a unique particle filtration and water removal system. They prevent destructive contaminants from entering industrial equipment as air is breathed in and out due to thermal expansion or fluid level changes. They provide a clear visual indication for replacement, as the silica changes color from orange to dark green when fully saturated.

There are multiple models available to accommodate air flows from 5 to 20 CFM with water retention capacities ranging from 0.2 lbs to 0.18 lbs, all with an absolute particulate filtration level of 2 micron.


  • Water Vapor Adsorbent – The silica gel used adsorbs up to 40% of its own weight.
  • Color Indicator – When maximum adsorption is reached the silica gel turns from orange to dark green, indicating replacement is needed. The silica gel used is chemically inert, non-corrosive, and does not contain cobalt chloride, a heavy metal. The color changing dye used is environmentally safe and meets all health and safety requirements.
  • Dual Filtration System – A two micron filter (99% efficiency) is located at the top and bottom of the silica gel bed. The top filter removes particle contamination from atmospheric air and the bottom helps with dust created by the silica gel beads contacting each other
  • Activated Carbon – As air is expelled, it passes through activated carbon which removes oil vapors, fumes, and odors (except for part numbers 39131, 39132, 39133, and 39134).
  • Bi-directional air flow – A 360º air flow allows air to be breathed in and out as fluid level changes or differential pressures occur. Expelled air “backflushes” the particulate filter to prolong the life of the breather
  • Durable construction – Watchdog® Desiccant Breathers are manufactured from rugged ABS plastic and impact modified acrylic.
  • To install Watchdog® Desiccant Breathers use one of several Watchdog® Breather Adapters
Model No. Description Height Dia Connection Air Flow Fluid Volume Exchange Silica Gel Volume Water Capacity
39100 Breather 4.75 in 5 in 1" Male Friction Fit 20 CFM 150 gpm .8 lb .2 lb
39101 Breather 6.25 in 5 in 1" Male Friction Fit 20 CFM 150 gpm 1.4 lb .4 lb
39102 Breather 9.25 in 5 in 1" Male Friction Fit 20 CFM 150 gpm 2.7 lb .9 lb
39108 Breather 11.25 in 5 in 2" Male NPT 20 CFM 150 gpm 3.5 lb 1.3 lb
39131 Breather 2 in 2 in 1/2" Female NPT 5 CFM 37 gpm .08 lb .032 lb
39132 Breather 3.25 in 2 in 1/2" Female NPT 5 CFM 37 gpm .1 lb .056 lb
39133 Breather 2 in 3.25 in 1/2" Female NPT 5 CFM 37 gpm .3 lb .104 lb
39134 Breather 3.25 in 3.25 in 1/2" Female NPT 5 CFM 37 gpm .5 lb .18 lb


Nominal Air Flow Rate 20 CFM (150 gpm of fluid volume change)
5 CFM (37 gpm of fluid volume change)
Particulate Filtration Level 2 micron absolute (99% efficiency)
Operating Temperature Range -20º to 200ºF / -28 to 93ºC
Silica Gel Adsorption Up to 40% of its weight of water
Material ABS plastic and impact-modified acrylic

Listed below is the maximum water capacity for the Watchdog® Desiccant Breathers by part number

Model No. Silica Gel Content Max. Water Capacity
39100 0.8 lbs 4.91 floz
39101 1.4 lbs 8.6 floz
39102 2.7 lbs 16.56 floz
39108 3.5 lbs 21.47 floz
39131 0.08 lbs 0.49 floz
39132 0.1 lbs 0.92 floz
39133 0.3 lbs 1.84 floz
39134 0.5 lbs 3.06 floz

Note: Water capacity is a function of relative humidity. At higher humidity levels, the silica gel adsorbs (holds) a larger amount of water. The maximum is approximately 40% of the weight of the silica gel at about 90% humidity.

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