How Desiccant Breathers Control Contamination
To combat the ingression of particles into oil systems, breathers are often attached to reservoirs and other oil storage components. Whether they are connected to an expensive piece of machinery or a drum of oil, breathers offer the peace of mind that as the oil level fluctuates, the air filling the space will be properly cleaned and mostly free of contaminants.
Desiccant breathers provide a wide range of benefits and are becoming more common. However, you may wonder how a plastic cup full of what looks like plastic beads actually filters incoming air and removes not only harmful particles but also water vapor, which is so dreaded in lubrication systems. The answer involves chemistry.
These breathers use the inherent qualities of two of nature’s most absorbent materials - silica and carbon. Everyone likely has opened a package and found little packets marked “Do not eat.” This is the same silica in desiccant breathers. How it works is quite simple. Silica is a very porous material that can trap and hold nearly 40 percent of its weight in water. As water vapor passes around these beads, it is trapped in the pores of the silica. Any water vapor that isn’t trapped by the silica goes through a layer of activated carbon.
Electronegativity is a chemistry term used to describe an element’s attractive force toward other elements. Carbon and oxygen both have high values and are attracted to each other to form new gases, such as carbon dioxide. Water vapor attaches to carbon by this force. The oxygen in the water binds with the activated carbon in the breather, thus preventing it from going any farther.
Most breathers also have a color-change indicator that shows when their useful life is up. This is accomplished with a water-reactive reagent embedded into the body of the silica. As water vapor attaches, it reacts inertly with the reagent, making it change its color.
Desiccant breathers generally have a synthetic fiber filter at the top to trap larger solid particles such as dust or organic material in the atmosphere. Next, there is a device called a diffuser, which takes incoming air and forces it through the entire volume of silica evenly. After the diffuser is the activated carbon, which serves to remove anything left after the initial filtration. As the container exhales, this process takes place in reverse, with the activated carbon absorbing the oil mist so as not to allow it back into the mass of oil after being in contact with other contaminants.
It is recommended that these breathers be installed in tandem with a vacuum gauge. In the case of dry environments, there may not be enough moisture ingression to cause a color change of the silica beads before the top layer of the synthetic filter is clogged with dust and other contaminants. A vacuum gauge will provide a visual signal as to when this occurs, since the air will not be able to pass through the entire breather.
3 Key Properties of a Breather
Desiccant breathers can help control both moisture and dirt ingression. A good desiccant breather system is one that:
- achieves the target level for cleanliness and dryness,
- has the capacity to enable a suffici
- ent service interval between change-outs,is easily visible for routine inspection during preventive maintenance.
As with most spin-on breathers, desiccant breathers often have a beta rating associated with them. This is a mark of how well the filter removes incoming contaminants.
Among the other criteria to keep in mind when selecting a filter is the cleanliness of the environment, which can affect its life expectancy. Obviously, the dirtier the air, the more particles the breather will trap. The amount of moisture or humidity in the air will determine how long you can go between filter changes.
The criticality of the machinery the breather is attached to is important to consider as well. If the machine operates on close tolerances with little room for particle ingression, you may need to get a high-quality breather and change it more regularly.
To maximize a breather’s efficiency, ensure the headspace of the oil level is sealed tightly. The volume being protected should breathe only through the filter installed. A loose seal will defeat the purpose and allow a straight path for outside particles to enter the system.
Although breathers are relatively easy to install, the process of how they work is quite involved. Pairing science with real-world need provides the advantage required to tackle the challenges of particle ingression and maintaining the small fluid film on which this industry rides.
