guardian protects hydraulic power unit
Greetje Wesselink

The complete story about desiccant breathers


Why breathers are important

Desiccant breathers are important because they prevent moisture, dust, and other contaminants from entering equipment that relies on oil-filled transformers, gearboxes, and hydraulic systems. This is important because these contaminants can cause corrosion and other forms of damage to the equipment, reducing its lifespan and potentially leading to costly repairs or replacements. By using a desiccant breather, the equipment is protected and operates more efficiently, extending its lifespan and reducing maintenance costs.

Desiccant breathers are designed to replace the traditional vent cap on lubricant reservoirs.

  • Most OEM installed vent/fill caps use steel wool, fiber or paper to block 10 - 40 micron particles and nothing to block moist airflow.
  • Up to 80% of the moisture in a gearbox, hydraulic system or circulating lubrication system enters through the breather.

OEM vent cap

Industries Served

Desiccant breathers are commonly used in a variety of industries including:

  1. Power generation: To protect oil-filled transformers, generators, and other power generation equipment.
  2. Manufacturing: In industries such as steel, paper, and petrochemical to protect gearboxes, hydraulic systems, and other lubricated equipment.
  3. Mining: To protect heavy-duty equipment such as trucks, bulldozers, and excavators.
  4. Agriculture: To protect tractors, combines, and other farm equipment.
  5. Construction: To protect cranes, bulldozers, and other construction equipment.
  6. Transportation: To protect train locomotives, shipping containers, and other transportation equipment.
  7. Oil and gas: To protect oil rigs, pipelines, and other oil and gas equipment.

These are just a few examples, but desiccant breathers can be used in any industry where protecting oil-filled equipment from moisture, dust, and other contaminants is important.


Desiccant breathers are used in a wide range of applications to protect oil-filled equipment from moisture and contaminants. Some common applications include:

  1. Transformers: To prevent moisture from entering the oil, which can cause insulation breakdown and lead to power loss.
  2. Gearboxes: To prevent contaminants from entering the gearbox oil, which can cause wear and damage to the gears.
  3. Hydraulic systems: To prevent moisture and contaminants from entering the hydraulic fluid, which can cause corrosion and affect the performance of the system.
  4. Fuel tanks: To prevent moisture from entering the fuel, which can cause corrosion and cause problems with the fuel system.
  5. Compressors: To prevent moisture and contaminants from entering the compressor oil, which can cause wear and damage to the compressor.
  6. Bearings: To prevent moisture and contaminants from entering the bearing lubricant, which can cause wear and reduce the lifespan of the bearing.
  7. Diesel engines: To prevent moisture from entering the engine oil, which can cause corrosion and affect engine performance.

These are just a few examples, but desiccant breathers can be used in a wide range of applications to protect oil-filled equipment from moisture and contaminants.

Find the perfect Breather for your application

The Benefits of Desiccant Breathers

Desiccant breathers offer several benefits, including:

  1. Protection against moisture: Desiccant breathers prevent moisture from entering the oil, which can cause corrosion and other forms of damage to the equipment.
  2. Protection against contaminants: Desiccant breathers also prevent dust, dirt, and other contaminants from entering the oil, which can cause wear and other types of damage.
  3. Improved equipment performance: By protecting the equipment from moisture and contaminants, desiccant breathers help to maintain its performance and efficiency.
  4. Extended equipment lifespan: By protecting the equipment from damage, desiccant breathers help to extend its lifespan, reducing the need for costly repairs or replacements.
  5. Easy maintenance: Desiccant breathers are easy to install and maintain, making them a convenient solution for protecting equipment.
  6. Cost savings: By protecting the equipment and extending its lifespan, desiccant breathers can help to reduce maintenance costs and save money over the long term.

Overall, the use of desiccant breathers can improve equipment reliability and performance while reducing maintenance costs, making them a valuable investment for a variety of industries and applications.

How Air Sentry Breathers work

A reservoir vent allows air pressure within a reservoir to equalize with the ambient  environment. Variations in air pressure created by  thermal expansion and contraction, fluid level changes created by pumps, motors or the filling  and emptying process drives the airflow.

This ebb and flow of air pressure exposes lubricants to the two most damaging contaminants – water and dust particles.

  • Lubricants are naturally hydroscopic drawing  moisture from humid air.
  • Condensation forms on the inside surfaces as  equipment cools.
  • Desiccant breathers ensure CLEAN, DRY AIR!

The working of the breather explained

  • A desiccant breather (cartridge) should be replaced when the silica gel is totally  green. Doing so allows the user to get full value from the breather.

More Silica - Longer Life - Less Cost

When silica gel turns green, air can still flow through the air vent, the particulate filter traps dust; the process of blocking moisture in the air comes to an end.

Water, often ignored, can be the  primary root cause of equipment failure.

Accumulating water can be found in three forms:

Accumulating water contamination in lubricant base oils can have significant effects on the performance and quality of the lubricant. Some of these effects include:

  • Corrosion: Water contamination can cause corrosion of metal surfaces, which can lead to wear and tear of machinery parts.
  • Oxidation: The presence of water can accelerate oxidation of the base oil, which can result in the formation of harmful by-products that can shorten the lifespan of the lubricant.
  • Decreased viscosity: Water contamination can dilute the lubricant and lower its viscosity, making it less effective at reducing friction and wear.
  • Emulsification: The presence of water can cause the formation of an emulsion, which can alter the texture and appearance of the lubricant and make it less effective.
  • Microbial growth: Water contamination can provide a breeding ground for bacteria and other microorganisms, which can cause further degradation of the lubricant and harm machinery.
  • Aeration – water encourages foaming  and air entrapment

Therefore, it is important to monitor the water content of lubricants and to take steps to reduce or remove water contamination to maintain the quality and performance of the lubricant.

Condensation inside air filter

The life of a desiccant breather is determined by:

  • The number and volume of air cycles passing  through the silica gel.
  • The amount of silica gel.
  • The humidity in the environment.
  • Contamination (water) in the lubricant when the  initial breather is installed.
  • The airflow requirement (CFM) for a reservoir (tank) is determined by the maximum  potential fluid level change (flow) for that reservoir.
  • The maximum fluid level change is typically caused by the filling and emptying process or  by hydraulic pumps and motors.
  • For every 7.5 gallons of fluid level change, 1  cubic foot (CFM) of air flows in or out the  vent.

Example = 75 GPM equals 10 CFM

Selecting 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.

Connection Size:

Identify the breather mounting location; the  best location is often the exiting 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..

d-series breather specificationD-series

Have a look at all desiccant breather specifications

Select a model with sufficient air flow to exceed a reservoir’s maximum  potential air flow requirement.

If necessary, mount two or more breathers on reservoir.

Breather Mounting

  • Remote mount to distance a breather from heat  (recommended above 65º C) using an extension hose or pipe.
  • Remote mount to distance a breather from heavy vapors, foaming and splashing fluids. Silica gel, when coated by a lubricants, becomes ineffective.
  • Remote mounting prevents a gearbox sling oil lubricator splashing or slinging oil into a desiccant breather.

Breather Misapplications

Some common misapplications include:

Using the wrong type of desiccant breather: Different types of desiccant breathers are designed to remove moisture from different types of fluid. Using the wrong type of breather can result in poor performance or even damage to the equipment.

Installing the breather in the wrong location: The desiccant breather should be installed in the right location to effectively remove moisture from the fluid. Installing it in the wrong location can lead to reduced efficiency or even complete failure.

Not considering the environmental conditions: The desiccant breather must be chosen based on the environmental conditions in which it will be used, such as temperature, humidity, and exposure to dust and other contaminants.

Overlooking maintenance: Desiccant breathers need to be maintained to ensure their effectiveness. Neglecting maintenance, such as not changing the desiccant, can result in the breather becoming clogged and ineffective.

In summary, proper selection, installation, and maintenance of desiccant breathers are crucial to ensure their effective operation and avoid misapplication issues.

Breather Solutions

Desiccant breather solutions are designed to help prevent moisture, dust, and other contaminants from entering fluid reservoirs and contaminating the fluid inside. Some common desiccant breather solutions include:

Silica gel breathers: Silica gel is a commonly used desiccant that absorbs moisture effectively. Silica gel breathers are available in different sizes and configurations, and can be used in a variety of applications.

Molecular sieve breathers: Molecular sieves are a type of desiccant that work by adsorbing moisture from the air. They are often used in high-humidity environments where silica gel is not effective.

Activated carbon breathers: Activated carbon is another type of desiccant that is used to absorb moisture and eliminate odors. Activated carbon breathers are commonly used in applications where air purity is critical.

Combined breathers: Some desiccant breathers use a combination of silica gel, molecular sieve, and activated carbon to provide multi-stage protection against moisture, dust, and other contaminants.

From left to right: silica, molecular sieve and activated carbon breathers

In addition to desiccant breathers, there are also breather filters and hydrophobic breathers that are designed to provide protection against moisture and other contaminants. The best solution will depend on the specific application and environmental conditions.

Air Sentry offers 8 different series with  multiple models.

For most applications, there are three possible solutions:

  • GOOD: Completely disposable, providing the  lowest initial cost of installation.
  • BETTER: Check valve design provides a  longer service life than disposable models.
  • BEST: The best value, lowest total cost of operation, extended service life.

Good Solutions

Limited Space Applications or minimal airflow requirements

Gearboxes • Drums • Totes •  Small Oil Containers

Mounting connection: 1/2” Female NPT

Better Solution

High Humidity / High Dust Applications

Paper Mills •  Wash-Down Areas • Steam-Cleaning Rooms • Mine  Quarries

Incorporates check valves in the reusable top cap and a  replacement cartridge

Check Valve PSI In/Out: 0.1 PSI to 2.1 PSI (varies by model)

Mounting Connections: Slip fit, ½” NPT, 1” NPT, 2” NPT

Best Solution


The Guardian - Ideal for Most Applications

  • The only desiccant  breather series that Air Sentry recommends for diesel fuel applications* (not recommended for other fuel applications)
  • *Guardian breathers used on diesel fuel applications must be accompanied with an isolation check valve. See Guardian models ending in NC, NG,  NGC.
  • Not available in models ending in N.
  • Established a new standard for performance and longevity
  • Lowest total cost of ownership as compared to other  breathers
  • Tritan™ construction provides the best combination of  chemical, temperature and impact resistance for desiccant breathers.


Guardian Breather Benefits

Guardian Breather Features

  • Tritan™ is BPA-free, recyclable and made  without halogens, sulfur, nitrogen, lead, mercury,  cadmium or hexavalent chromium – keeping  these materials out of the environment.
  • The aluminum mounting ring molded into the  base adds strength and vibration resistance.
  • Mounting connections include 1”NPT, 2”NPT and  1”BSP

Guardian Breather Replacement Cartridges

Breather replacement cartridges are replacement components used in desiccant breather systems. They contain the desiccant material that absorbs moisture and other contaminants from the air that enters a fluid reservoir. Breather replacement cartridges can come in different forms, as indicated above.

Breather replacement cartridges are a crucial component of desiccant breather systems, as they ensure that the system remains effective over time. Regular replacement of the cartridges is essential to maintain the performance of the system.

  • Replacement cartridges reduce waste and lower replacement cost.
  • Replacement cartridge are priced near the disposable breather price level.
  • Cartridge lengths include 5”, 8” and 12”

Guardian Specifications

  • Check Values (8): In/Out 0.1 PSI
  • Particle Filter: 2 micron absolute (2, cartridge top  and bottom)
  • Mounting Connection (Female): 1” NPT, 2”NPT,  1”BSP
  • Maximum Air Flow: 25 cfm
  • Maximum Fluid Flow: 187 gpm
  • Replacement Cartridges: 5”, 8”, 12”
  • O Ring Seals: Top Cap and Base
  • Compound Indicating Gauge: Optional
  • Isolation Check Valve: Optional (Recommended)

Guardian Modular add-ons

Guardian Applications

Vapors and moisture released during tank filling operations can contaminate silica gel.

Check valves in the  Guardian base combined with the Isolation Check Valve (optional) vent  harmful vapors to the atmosphere.

How to build a Guardian Model - part # G5 S 1N G C

Breather Applications


Railroad bridge enclosed gear drive:


  • Humid environment
  • 20 gallons of lubricant
  • No vibration
  • Long service interval
  • 1” NPT vent mounting connection

Gearbox Recommendations:

Lowest initial cost  

Longer life (2X times)
Cartridges lower replacement cost  Reduce labour cost installing breathers

Longest life (up to 4X times)  
Isolation Check Valve
Cartridges lowers replacement costs
Reduce labour cost install breathers (3X times)

Hydraulic Systems


  • Humid environment
  • 55 gallon reservoir
  • No vibration
  • Constant fluid level
  • Minimal air flow
  • 1” NPT vent mounting connection

Hydraulic System Recommendations:

Lowest initial cost  

Longer life (2X times)
Cartridges lower replacement cost  Reduce labour cost installing breathers

Longest life (up to 4X times)  
Isolation Check Valve
Cartridges lowers replacement costs
Reduce labour cost install breathers (3X times)

Storage tanks, drums and totes

Conditions Lubricant storage tanks:

  • Outdoor location
  • 2500 gallons
  • 3” ANSI mounting flange
  • Fluid flow rates 25 to 50 gpm
  • Air flow rates up to 7 cfm

Lubricant Storage Tanks Recommendations:


  • Longest life
  • Isolation Check Valve
  • Silica gel cartridges lowers replacement costs
  • Reduce labour cost installing breathers

The Guardian exhaust airflow, loaded with fluid vapors /mist out the base check valves. Silica gel dries incoming air only.

Lubricant outdoor storage tank