What are desiccant breathers and how do they work?

What are desiccant breathers and how do they work?

full-line-of-air-sentry-desiccant-breathersTo start at the beginning: according to the Cambridge Library desiccant means: "a substance used to remove moisture from something". Thus: a desiccant breather removes humidity out of the air as it is passing through a filter. The goal is to dry the air before it enters your precious reservoir.


What about a vent cap?

A vent cap is simpler, easier to place and a cheaper solution, but.......

Equiment OEMs include breather caps on the fill port to allow expanded air to escape. However, there is one problem: while the vent caps let air out, they don't prevent small, dirty particles and moisture from entering the equipment. And there the problems start:


  • Moisture will condense inside your reservoir and water is entering your lubricants. Water can accelerate the oil's aging rate
    tenfold, resulting in sludge, varnish.....

  • Dirt particles can damage bearings, valves and gears by wearing away the critical surfaces.

What If a desiccant breather would not exist?


Then following problems would arise:


  • harmful contaminants
  • component wear
  • fluid degradation
  • equipment failure
  • rust and oxidation


..... and your fluid would look like this: ↓
















condensation - rust - oxidation - particulates - sludge - corrosion ..............





The wide range of Air Sentry desiccant breathers are designed to replace the breather cap on:


  • bulk storage tanks,.
  • boxes
  • oil drums
  • gear boxes
  • hydraulic fluid reservoirs
  • oil-filled transformers
  • other fluid reservoirs.

The breathers adsorb water from the air before it enters your fluid system AND remove particulate contaminants as small as 2 microns.


How does a desiccant breather work

cut-away-drawing-of-a-desiccant-breatherThe image on the right indicates how the desiccant breather allows outside air to enter through the 360° opening in the breather’s top cap. The top cap design overhangs the body of the breather helping protect the breather from rain, sleet, snow, as well as most equipment wash-down procedures.


  • When contaminated air enters the top of the breather, it passes through a self cleaning solid particle filter. This filter traps solid particles greater than 2 micron and keeps them from entering the breather and ultimately to wear surfaces on your equipment.

  • The filtered air then passes through a bed of silica gel that adsorbs moisture in the air. During this step up to 95% of the water vapor in the air is filtered out.

  • Finally, the filtered air passes through an additional 2 micron filter in the bottom of the breather to ensure that no harmful particles will enter the tank or reservoir.

This three stage filtration design ensures your equipment gets CLEAN, DRY AIR!


As the color indicating silica gel adsorbs moisture it changes from gold to dark green. When the silica gel is adsorbed to its capacity (approximately 40% of its original weight), the breather has fully turned dark green. This color change is easily seen and serves as the visual indication that it is time to remove and replace the disposable breather.



green means clean



The diagram below indicates air being expelled back through the desiccant breather from the equipment the breather is mounted on.


cross-section-of-a-desiccant-breatherAs contaminated air travels this reverse path, expelled water vapors are adsorbed by the silica gel. During this reverse air flow process, the silica gel indicates the presence of excessive moisture inside the reservoir as the gold silica gel turns to dark green from the bottom of the breather rather than from the top of the breather.


An additional feature located in the bottom of most Air Sentry® models is a layer of carbon impregnated foam. This carbon pad absorbs small amounts of oil vapor exhaled from the tank and protects the silica gel from minor oil mist contamination.


Excessive oil mist control may be required. Adapters are available for applications with excessive oil mist problems.


As the exhausted air passes back through the self cleaning 2-micron filter, located in the top cap of the breather; any particles that were trapped as air entered the system are now back flushed from the filter.



Desiccant Breathers are the start of contamination exclusion




Air Sentry Products - the gold standard in contamination control

Air Sentry products are powerful preventive maintenance tools and cover a wide range of application requirements. The line consists of Good, Better and Best options designed to meet your specific application and duration specifications.




Air Sentry D-series desiccant breathers

  • The models in this group satisfy most applications involving hydraulic reservoirs, lubrication and fuel storage tanks,
    transformers, pumps and gearboxes.
  • Models D-100, D-101 and D 102 are rated for airflow of 35 cfm.
  • Model D-108 is rated for 100 cfm.
  • Type of medium: 100% sillica gel.
  • Max. air flow/fluid flow: 20 cfm / 150 gpm.




Air Sentry Z-series desiccant breathers

  • These are the “Mini Breathers”.
  • They are designed for applications where space is limited or airflow is minimal (10 cfm or less).
  • They are often used for gearboxes, drums, totes and small reservoirs.
  • Type of medium: 100% silica gel.
  • Max. air flow/fluid flow: 5 cfm / 37 gpm.




Air Sentry X-series desiccant breathers

  • The X-Series Breather line was designed for extreme humidity.
  • Ideal environments include paper mills, or anywhere that humid air is a problem.
  • The X-Series models incorporate check valves that allow air to enter through the breather only when required,
    thereby extending the life of the desiccant and the useful life of the breather.
  • Type of medium: 100% sillica gel.
  • Max. air flow/fluid flow: 20 cfm / 150 gpm; except X-100 is: 10 cfm/75 gpm.





Air Sentry Guardian-series desiccant breathers

The GUARDIAN takes check valve technology and cost-saving replacement measures to the next level. Air Sentry also introduces four exclusive advancements that will again raise the bar in contamination control:


Tritan™ Construction

This patented material is the most chemical, temperature, and impact-resistant breather on the market.


Isolation Check Valve

The isolation check valve isolates the desiccant from exhaust air to lengthen service life of the desiccant while also protecting it from volatile and splashing fluids.


Integrated Compound Vacuum / Pressure Gauge

This proprietary feature is a true-life accurate indicator of filter conditions.



Stack cartridges to extend the life of breathers even further using the Modular Stack Ring™.




For more information download the brochure:




How to select the right breather model

Determine CFM requirement:

  • Select a model that exceeds a reservoir's air flow requirement (CFM).
  • Include a margin of safety.


Choose the Right Series:

  • Consider the environment;
  • select a model that best fits the challenges of the application.
  • Environment examples - vibration, mobile equipment, high humidity and extreme dust.


Determine Connection Size:

  • Identify the breather mounting location; the best location is often the existing vent.
  • Select a model with a similar mounting connection.
  • If necessary, it’s ok to use an adapter / reducer.
  • Be careful not to restrict airflow.


Evaluate Mounting Area:

  • Evaluate the available space for the breather.
  • If space is limited or other issues apply (heat, oil mist, vibration, etc.), remote mount the breather.
  • Remote mount using an extension pipes, hoses, adapters etc.


Typical Industries and Applications

Aluminum Extrusion, Forging & Rolling Mills

  • Hydraulic Systems
  • Gear Reducers
  • Storage tanks


Appliance Manufacturing

  • Hydraulic Presses
  • Gear Reducers
  • Air Systems
  • Robotics


Pulp & Paper

  • Gear reducers
  • Hydraulic systems
  • Turbine Oil systems
  • Calander stack bearing oil systems


Steel Mills & Foundries

  • Hydraulic systems
  • Gear Reducers
  • Rolling Oil systems
  • Storage tanks



  • Vacuum Systems
  • Air exchange and control systems


Chemical & Petrochemical

  • Process systems
  • Lube Oil degassing and conditioning
  • Turbines
  • Storage Tanks
  • Gear Reducers
  • Transport Tanks

Keep dirt and water out of oil


Desiccant breathers are preventive maintenance tools.

They protect your equipment.

But contamination control cannot be reached by desiccant breathers only. You will also need:

  • application of seals
  • use of system filters
  • proper sampling techniques
  • lubricant storage/disposal systems

By using these solutions together, life of machine and lubricant can be maximized and capital and operating expenses be minimized.


Enluse offers a full line of desiccant breathers.

For more information please have a look at our website or contact us.



Almost forgot the best part: ROI

  • fewer breakdowns
  • fewer production stoppages
  • less waste
  • more efficiency
  • increased working life of lubricants
  • increased working life of equipment

Let us help you finding the right breather for your application. The first step to extend a system's life.

Air Sentry®

“The First Line of Defense In Contamination Control”

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