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 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.

 

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. 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.

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.

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 gold and turn dark green 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:

• 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.