Types of breather filters, their importance, and industrial applications

All hydraulic systems breathe. When actuators expand and retract, the fluid flows into and out of reservoirs, and along with it comes air. This air transports dust, moisture, and metallic particles as well as other substances that, once in the system, start attacking seals, blocking valves, and also accelerating the process of degradation. A breather filter is located near the vent of the reservoir and stops the pollution before it enters. It's among the most simple components in a hydraulic circuit; however, it's also among the least understood, and when it fails or is unmaintained, the results affect the whole system.

This article outlines the most common kinds of breathing filters, the factors that make each one appropriate for various contexts, and the ways in which each one is utilized in industry.

What is the significance of breather filters?

The reservoirs of hydraulic fluid are not sealed systems. As the fluid level decreases in operation, it draws on air to make up for the drop. As the fluid levels rise, that air is ejected. This breathing cycle continues in the course of machine operation.

The issue is that the ambient atmosphere is not always free of contaminants. In industrial settings air is filled with fine particles of material, water vapor, along with chemical vapors. ISO 4406 cleanliness standards, which regulate contamination of particles in hydraulic fluids, are susceptible to being compromised within just days of operating if the ingestion of reservoirs is not managed. Moisture is especially harmful to the hydraulic oil, as water reduces the lubricity of the oil, speeds up the process of oxidation, causes corrosion on metal surfaces, and stimulates microbial growth in biodegradable fluids.

Breather filters tackle everything right at the point of entry. Instead of treating any contamination that has already been introduced through the filter, they block entry into the system in the first place.

Breather filters of various types

1. Standard particulate air breathers

The simplest and the most popular type is the one that contains an artificial or fibrous filter media that has been calibrated to a particular micron scale—typically between 3 and 25 microns. The media are able to pass through air throughout each breath cycle, and particles are absorbed by the filter component.

Standard particulate breathers can be found in threaded caps that can replace the original cap on the reservoir's breather, which makes retrofitting easy. They're affordable and can be adapted to clean environments in which particulate matter is the main issue. They are generally certified for airflow capacities that are suitable for small to mid-sized hydraulic systems.

Mobile hydraulic machinery – excavators, loaders, and agricultural machinery – the outdoor dust is normal; however, humidity is low.

2. Desiccant breather filters (Hygroscopic breathers)

Desiccant breathers go beyond by combining particulate filtration and absorption of moisture. They have silica gel, or a molecular sieve, that eliminates water vapor from the air that enters before it is absorbed by the fluid. A majority of units include an airborne particulate pre-filter at the inlet and a post-filter for the side of the fluid for double protection.

The most obvious measure of performance is the ability to change color that silica gel exhibits. Desiccant that is fresh will typically be either orange or blue. As it gets saturated, it transforms into white or pink, providing maintenance personnel a clear indication of replacement without having to disassemble the equipment.

Desiccant breathers can be rated based on their capacity for water absorption—typically measured in gallons of water per unit—as well as their particle filtration ratings. For environments with high humidity, selecting the right desiccant volume to support the expected breathing rate is essential.

Hydraulic systems, offshore industrial plants on the coast, food and beverage processing facilities, injection molding equipment, as well as any indoor industrial setting that experiences significant fluctuations in humidity, like factories that have large bay doors on a regular basis.

3. Combination breathers (Particulate + desiccant + check valve)

Certain breather filters include the check valve mechanism that is used to limit reverse airflow from both sides of the exhaust. This stops moist air from re-entering the desiccant even when the system is in rest and extends the life of the desiccant. Other systems add a second phase of desiccant beneath the particulate filter so that moisture is captured both egress and ingress.

Combination units that have high capacity are built for reservoirs with large volumes in which the rate of breathing is high, for example, large press systems or hydraulic central units that feed multiple machines at the same time.

Steel mills' huge injection molding presses, centralized power systems for hydraulics within manufacturing plants, as well as the wind turbine's hydraulic system in which access to replacement is difficult and service intervals must be extended.

4. Filters for breathers with a spin-on design.

The spin-on design is based on the popular spin-on design of the hydraulic return filters These units are threaded directly into a standardized head and are able to be changed quickly with no tools. Spin-on design is popular in fleet maintenance, in which speedy service delivery is a major factor.

The filtering media used in spin-on breathers may be synthetic, glass fiber, or a desiccant mix based on the specifications. They typically have higher-rated airflow than cap-style breathers and can be found in a greater variety of micron ratings.

Mining machinery as well as industrial hydraulic units manufacturing, where replacement of filters is a regular part of the PM schedule.

5. Industrial breathers with high flow.

In massive stationary systems, such as a hydraulic press equipped with a 1,000-liter reservoir or test equipment with a high-cycle-rate actuator, the amount of air exchanged in a cycle is way over what a typical breather with a cap can handle. High-flow industrial breathers are big-format breathers that have wide-area filtering media and low restrictions and the highest airflow ratings.

They are usually portable and flanged to allow direct integration into the covers of reservoirs or vent manifolds. They typically have multiple stages, including coarse pre-filtration, fine particulate filtration, as well as desiccant in a single series.

Hydraulic power units are used in the steel industry, big press machines for casting dies, testing stands, hydraulic circuits, and paper milling machinery.

The right breather filter to choose

Airflow capacity. The breather's airflow rating must be matched to the maximum displace rate in the reservoir. Breathers of inadequate size create back pressure at the vent. This may lower the level of fluid or trigger air aeration.

Filtration ratings. The desired ISO cleanliness code of the system determines the micron count required. Systems with sensitive servo valves and proportional valves generally aim for ISO 4406 codes of 17/15/12 or higher, which require sub-10-micron breather filtering.

Moisture exposure. Any place with an average relative humidity of more than 60% or significant temperature fluctuations that result in condensation is a reason to have the use of a desiccant breathing device at a minimum.

The compatibility of service intervals. The breather's filter is saturated or gets blocked more quickly than your machine's PM interval can create an unclean window. The desiccant capacity and the particulate holding capacity are in order to be aligned to the schedule of maintenance but not to minimize the upfront cost.

Considerations for maintenance

They are inactive elements; that means they're easily forgotten—up until the point they break. The most typical failure scenario isn't a major rupture but rather a gradual occlusion. If the filter becomes clogged, the restriction becomes more severe, and the system starts taking in air through other routes (around sealing seals on shafts and/or through loose connections) that do not offer any filters in any way.

In the case of breathers that are particulate-only, replacing is the primary maintenance job. For desiccant units, the indicator's color provides the trigger based on the condition. In both cases, recording the condition of the breathing system throughout each maintenance interval and then replacing it proactively rather than relying on failure is the best method.

Breather filters take up a tiny area within the hydraulic circuit, but they protect an extensive area. Every liter of liquid moving into or through a storage reservoir represents an opportunity to introduce contamination, and an appropriately designed breather can stop that possibility with minimal expense compared to the protection component gives. For maintenance teams that already invest in the analysis of fluids, cleaning, monitoring cleanliness, and condition-based programs to replace filters, breather filters are the most appropriate starting points since the downstream filtration strategies do not compensate 100% for contamination that wasn't removed in the first instance.