Desiccant Breathers: A Complete Guide

Jonathan Trout, Noria Corporation

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

  • High capacity air filters are ideal for extremely dirty or dusty conditions.
  • Manual indicator vacuum gauges serve as a visual of when your breather needs to be replaced. In the case of breathers operating in dry environments, there might not be enough moisture coming in to cause the silica to change color before the first particle filter is clogged with dirt and debris. A vacuum gauge is a good way to get a visual when this happens.
  • Wash-down caps are ideal for equipment needing to be washed down regularly (food processing, mining, cement, paper facilities) or equipment in dusty environments. They prevent water from entering the breather and headspace.
  • Isolation check valves keep the desiccant from coming into contact with exhaust air which helps lengthen the life of the desiccant and protects it from fumes and splashing oil.


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?

  • Increase the distance from the bottom of the breather to the top of the reservoir. Instead of attaching the desiccant breather directly to the reservoir, add a small length of pipe in between to help the breather stay clear of any oil mist coming up out of the reservoir.
  • Use a breather with check valves or a bladder system that reduces the amount of air filtered by the desiccant inside the breather. With check valves or bladders, only the air that needs to be inhaled in is dried, lengthening the life of the silica gel.


How to Choose the Right Desiccant Breather

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

  • What is the environment?
  • What is the application?
  • What is the average and maximum airflow rate?
  • What is the maximum reservoir capacity?
  • Is the operation intermittent or continuous?

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:

  • Disposable stationary applications: These include gearboxes, fluid reservoirs, transformers, pumps and storage tanks.
  • Limited space applications: Applications with limited space include gearboxes, drums, totes and small oil containers.
  • High humidity/dust applications: Paper mills, wash-down areas, steam cleaning rooms and mine quarries are good examples of high humidity applications.
  • High vibration applications: Equipment like cranes, railroad maintenance vehicles, construction vehicles and off-road trucks could all benefit from a breather designed for vibration and mechanized shock.
  • Extreme environment applications: Exposed equipment like windmills and wind power turbines, mining equipment, farm equipment and off-road vehicles are common examples of equipment operating in extreme environments.
  • Caustic fumes/gaseous applications: Airport boarding jetways, hydraulic fluid reservoirs, forklifts and baggage haulers are common examples of this application.

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

  • Gearbox adapter kit: Gearbox adapter kits let you install desiccant breathers on most gearboxes. They allow oil to be pumped in or out without exposing the gearbox to the atmosphere. You can tackle offline filtration, oil changes and oil sampling all through the adapter.
  • Drum adapter kit: Drum adapter kits let you install breathers on any storage tank or drum. This adapter lets you store, filter and pump lubricants from a drum using quick connectors and single-port access to reduce contamination.
  • Hydraulic reservoir adapter kit: Hydraulic reservoir adapter kits let you install desiccant breathers on any hydraulic fluid tank or reservoir. They have quick-connects in two sizes for pumping oil in and out, so the system stays closed. Off-line filtration can also be achieved through this adapter without disrupting the breather or opening the tank.


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.

  • Deeter Foundry – A Case Study: Deeter Foundry produces gray iron castings used in manhole frames and covers, storm sewer inlet frames, grates and curbs, trench grating and tree grates. It started using desiccant breathers because the company noticed water contamination increased in hydraulic reservoirs during the summer months. They also found it difficult to maintain target ISO cleanliness codes.

    Through some trial and error with various filters, Deeter noticed spin-on oil filters worked like a breather but were very expensive. They finally tried desiccant breathers as a more affordable option. As a trial, Deeter was able to achieve target moisture and dirt levels over six months of using desiccant breathers. They upgraded their other systems to use desiccant breathers, starting with their large gearboxes. After 90 days, oil analysis reports showed a decrease in silicone levels and ISO cleanliness levels were being achieved at levels previously unachievable.

    Today, Deeter Foundry employs desiccant breathers on many types of machinery including air compressor separator exhaust, outside fan bearings, gearboxes, lubrication storage racks, bulk hydraulic oil totes, and all hydraulic units.

  • Oilseed Manufacturer – A Case Study: An oilseed processor in Eastern Missouri separates soybeans into value-added products like high-quality vegetable oil to produce various animal feeds and biodiesel fuels. Oilseed manufacturing is a high-cost operation, requiring high energy use and detailed maintenance to keep things running smoothly. Technicians are required to inspect, maintain and preserve the life of hydraulic fluids in oil reservoirs which recirculate through transfer pumps and reciprocating equipment.

    The company has been using desiccant breathers to keep moisture out of the oil, but they've been experiencing shorter breather life. They were looking for a cost-effective replacement to extend the operating life of their breathers and eliminate nearly all moisture re-entry using a breather with a check-valve technology.

    After a review of their operation and sizing requirements, the oilseed manufacturer was fitted with desiccant breathers with check-valve technology and saw a 25 percent increase in breather service life. Overall, this reduced maintenance costs and process downtime.

  • Oregon Hay Farming Operation – A Case Study: For this case study, a large hay farming operation in Oregon started experiencing critical problems with their $100,000 hydraulic hay press system that was less than a year old. This operation exports hay overseas requiring it to densely pack bales to 12 feet per side. It operates in a very extreme environment with ever-present severe dust and airborne contaminates.

    After an analysis of the machine's hydraulic oil, the company found high levels of contamination in the reservoir. It had already been doing a complete fluid change every six months at a cost of $7,500 each time. If the problem wasn't resolved, a complete press rebuild would be needed in just under a year at a cost of around $40,000.

    The company ended up replacing the hydraulic reservoir's breather caps with desiccant breathers featuring 100 percent silica gel for moisture absorption, 100 percent activated carbon for fume and odor control and two-micron solid particle filtration. After the implementation of these desiccant breathers, complete fluid changes went from being needed every six months to every 18 months, increasing oil service life over 300 percent and saving the company around $15,000 each year.


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.

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