Desiccant Breathers: A Complete Guide

Jonathan Trout, Noria Corporation
Tags: oil analysis

Desiccant breathers remove contaminants such as dirt and moisture from air entering machinery, sumps and reservoirs. Below we'll discuss how desiccant breathers work, how to choose the right one, how to install one and more.

Desiccant Breathers - Air Sentry

What is a Desiccant Breather?

Studies have shown that around 70 percent of equipment or machinery loss of use is due to surface degradation. Of that 70 percent, 20 percent of replacements are a direct result of corrosion and the other 50 percent are due to mechanical wear. The most common causes of this corrosion and mechanical wear are dirt and moisture originating outside the machine, also referred to as contamination. When you have moisture in your lubricant or hydraulic fluid, a myriad of negative effects start occurring. For example, moisture leads to corrosion, which in turn leads to particulate contamination. Moisture can also change oil viscosity, deplete additives and cause sludge formation. To fight back against these problems requires a holistic contamination control approach. For this reason, more companies are choosing solution-focused suppliers who offer the full spectrum of contamination control equipment from desiccant breathers to filters and other tools.

Before we can define a desiccant breather, we need to understand what a desiccant is. A desiccant is defined as a hygroscopic substance (material that attracts and holds water molecules) that induces or sustains a state of dryness in its vicinity. If you've ever opened a box of new shoes or a packet of beef jerky and seen those little packets labeled "do not eat," those contain silica gel, which is a desiccant. Other types of desiccants are used as well.

Desiccant breathers are multi-tiered devices installed on your machines to prevent the entry of two crucial contaminants: moisture and particles. Equipment like gearboxes, pumps and reservoirs must "breathe" when air in the headspace expands and contracts due to temperature changes and oil level changes in the case of hydraulic systems, incoming fluid displaces air or when hydraulic components are working. Each time equipment "breathes," dirt, debris and moisture are brought in, contaminating the lubricant and damaging the equipment over time. Since we know at least half of lubricant contamination comes from outside machinery and most machines are designed to "breathe," it's a good idea to stop these contaminants at the source. Enter desiccant breathers.


How Desiccant Breathers Work

Desiccant breathers vary in design and construction. Some work by using a three-stage design to help ensure the interior of your equipment stays clean and dry. Incoming air is cleaned and dehydrated through an initial solid particle filter, a container of silica gel and another solid particle filter. As our diagram shows desiccant breathers work like this:

  1. As the machine breathes, contaminated air enters the desiccant breather and goes through the first solid particle filter. This is typically filtering out particles two microns or greater.
  2. Next, the outside air is dehydrated through a container of silica gel desiccant which extracts the water vapor in the air.
  3. Finally, the outside air passes through a third two-micron solid particle filter at the bottom of the desiccant breather.

desiccant breather cross section

As the machine exhales, air travels through the desiccant breather in reverse, or may purge directly to the atmosphere depending on the breather's design. As the breather's silica gel becomes absorbed with moisture, it turns a different color. Color varies depending on the brand of desiccant breather but for example, the silica gel may start out blue and turn purple when fully absorbed with water. This is how you'll know it's hydrated and time to replace the filter.

Many desiccant breather models implement components to help extend the life of the breather. Carbon-filled foam filters on the bottom of the breather absorb any oil vapor or oil splashing up that could get into the silica gel of the desiccant breather, shortening its lifespan. Check valves and reusable tops help extend the life of the desiccant by providing a closed system until airflow is needed. In other words, if your desiccant breather is equipped with an intake check valve, airflow into the breather is only occurring when the differential pressure between the atmosphere and fluid reservoir exceed a certain threshold.

In addition to the carbon filters and check valves, other desiccant breather add-ons you may see include:

desiccant breather manual gauge


How Long do Desiccant Breathers Last?

A common question that comes up when discussing how desiccant breathers work is how long do they last? Most breathers last anywhere from three to six months if properly sized. The answer depends on three variables:

  1. Frequency and volume of air intake
  2. How much silica gel is in the breather
  3. How humid the work environment is

Intake frequency and volume of breathing refers to how much moist air passes through the breather.Each time a piece of equipment breathes, water vapor is retained in the silica gel, gradually shortening the life of the breather. The amount of water the breather can hold directly relates to the amount of silica gel in the breather. Most desiccant breather manufacturers have a chart with the maximum water capacity for each breather, so you'll know how much moisture the breather can retain before reaching the end of its life.

Humid work environments tend to shorten the lifespan of a desiccant breather. This is because as the humidity increases, the silica gel reaches its maximum moisture-holding capacity faster. Once this capacity is reached, no more moisture can be removed from incomping air.

So, how can you improve the life of a desiccant breather?


How to Choose the Right Desiccant Breather

There are multiple factors you need to consider before choosing a desiccant breather:

Your machine's operating environment should be considered as it pertains to the amount of contamination. For example, severe environments like those with water spray or large amounts of dirt should use a desiccant breather that can hold higher amounts of ambient contamination. Severe environments might require breathers with check valves to help prolong their lives.

The application refers to the type of equipment needing a desiccant breather or the type of work being done. Many desiccant breather models come in multiple sizes and in a series, depending on the application (what machinery you have or the kind of plant you're operating in). Typical application categories can be broken down as follows:

One of the most important factors to consider when looking at desiccant breathers is your airflow rate. Desiccant breathers are sized according to the required cubic feet per minute (CFM). Always choose a breather with a higher CFM capacity than the CFM requirements of your tank or reservoir. Installing a desiccant breather without enough airflow creates excessive pressure causing a vacuum which will damage the equipment. It is very important the breather doesn't restrict air to the point it creates lubricant flow issues inside the system. If you need to convert gallons per minute (GPM) to CFM, the breather manufacturer should have the corresponding GPM/CFM numbers for your reference.

The capacity of the reservoir often impacts how quickly the desiccant may be saturated with moisture. More oil equals more humidity in most cases. Reservoir capacity is also important to consider because the bigger the reservoir, the more headspace fluctuation there might be, which affects the amount of air moving through the breather. Each breather model has have different reservoir capacity requirements, so it's important to check the breather model number for specifics on the amount of desiccant to the reservoir capacity before making your final purchase.

Lastly, desiccant breathers are rated for either continuous or intermittent flow. This is usually important when it comes to whether the breather incorporates check valves to aid in the life of the breather.



How to Install a Desiccant Breather

The desiccant breather replaces your machine's breather cap or air filter. Installing a desiccant breather is a fairly straightforward and simple process, especially since many breather models are screw-on installation types. You can purchase adapter kits to install breathers on various types of equipment. Examples of available adapter kits include:

desiccant breather gearbox adapter drum adapaterhydraulic reservoir adapater


What are the benefits of a Desiccant Breather

As previously discussed, contamination from dirt, dust and particularly moisture enters equipment and machinery as it "breathes." Water-contaminated oil leads to additive depletion, oil oxidation, and rust and corrosion over time, shortening the life of your machinery. Desiccant breathers filter out moisture and debris, greatly reducing contamination and prolonging the life of machines and equipment. There are many real-world examples of how installing desiccant breathers have saved companies money by shortening the frequency of downtime and keeping equipment contamination free. Let's look at a few.


Desiccant Breather FAQs

What are some side-benefits of desiccant breathers that aren't immediately apparent?
The amount of oil mist exhaled from the headspace can be noticed from the oil collection on the desiccant. This is important because this oil mist impairs desiccant performance. Additionally, some might not know you can tell the amount of humid air intake by how fast the desiccant becomes saturated. Without the desiccant as a barrier, this moisture would come into contact with the oil.

What applications are desiccant breathers especially beneficial for and why?
Gearboxes, tanks, reservoirs and bearing sumps (process pumps, etc.) that are used intermittently can accumulate water from headspace condensation. Hydraulic reservoirs on systems with linear actuators (cylinders, etc.) take in air with each stroke of the actuators. This air can take on considerable amounts of water and dirt over time.

Oil systems with a fair amount of surge volume such as a hydraulic system, especially benefit from properly installed breather because the center of mass of the fluid is moved as part of normal operation, routinely creating vacuum and over pressured pockets and shifting the headspace to different high points.

What are some applications most end-users never think of?
Breathers can and often should be used on day tanks and containers used for dispensing lubricants. Standby equipment should also be fitted with breathers. Another rarely thought of application is attaching a desiccant breather to the bung of oil storage tanks.

What are the biggest mistakes users make when employing desiccant breathers?
Many machines don't need desiccant breathers due to the fact that they run continuously, and the oil runs very warm (usually above 150 degrees Fahrenheit). If water contamination and the consequences of water contamination have not been historically present, it may be a waste of time and money to install desiccant breathers.

Another mistake often seen is missed openings. Many sumps and vessels have more than one egress point installed. It's common to find a breather properly installed but immediately adjacent to another unsealed or potentially leaking opening.

What does balanced filtration mean?
In addition to moisture filtration, desiccant breathers need particle removal filters with sufficient holding capacity and capture efficiency (at size) to control particle ingression. Many breathers have very limited or overstated particle removal capability. If you need a 5-micron filter on your oil, for example, you need the same quality filter on the breather.

Can desiccant breathers be used more than once?
Many desiccant breathers are designed to allow dehydration of the desiccant by either passing instrument air (clean air) through the breather or by placing the desiccant in an oven for a couple of hours. Reusing the desiccant three to five times is possible as long as no oil has accumulated on the silica gel granules.