Types of breather filters, their importance, and industrial applications

Filters for the breather of hydraulics, commonly referred to as breathing tanks or breathers, block airborne pollutants from settling into a reservoir while the level of fluid increases and decreases in the normal operation of a cylinder. The primary kinds are desiccant breathers, regular particulate breathers, and combination (desiccant and particulate) breathers, as well as check-valve or ventilators that are filtered. The choice of the best type is based on the ambient humidity as well as the level of particle contamination and how often the system is cycled.

Why do hydraulic systems require air filters?

Every hydraulic reservoir "breathes." When cylinders expand and retract in their length, the volume of the fluid within the tank changes. Consequently, the tank is required to draw in air or expel it to balance internal pressure. Without a vent that is properly filtered which is properly filtered, air can carry dust or moisture as well as aerosolized debris straight into reservoir headspace, and ultimately, to the liquid in the reservoir itself.

Contamination that is introduced by an unfiltered or poorly-filtered breather is among the most prevalent -- and also the least preventable reasons for premature wear and tear on the components. Particulate contamination can cause abrasive wear on valves, pumps, and seals for cylinders, as moisture intrusion causes degradation of additives, oxidation, and microbial growth within the fluid. Both issues directly affect those ISO 4406 cleanliness targets that many systems are designed to keep.

A properly specified breather filter is a low-cost and high-leverage part. In comparison to an overhauled pump or scored rod, a cylinder breather is among the lowest insurance rates within the whole hydraulic circuit.

How does a breather filter work?

A breather filter is mounted on the top of the reservoir, typically plugged into the tank's vent or fill port. When the system is in use:

• Stroke of exhaust (fluid level increases): Air inside the tank headspace is forced out via the breather medium that traps the outbound particulate and, in certain models, oil mist.
• The stroke of intake (fluid level drops): Ambient air is drawn in by the same media. It is able to filter dust out and in desiccant units removes moisture before it gets to the headspace.

The filtration capacity of the breather component (commonly 3--10 micron) should be in line or even exceeded in relation to the cleanliness target of the system as a breather that is not matched can be the weak link in a well-filtered circuit.

Breather filters of various types

1. Standard particulate air breathers

They're the basic design of a tank: it has the pleated or depth-media element, which captures dust and particles that are blown in by the air when air flows through and out of the tank. They're usually rated in the range of 3-10 microns and can be used in indoor environments or moderately clean ones in which humidity isn't an issue.

safe indoor environments, machines, hydraulics for machine tools, injectors, as well as other applications where moisture penetration is very low.

2. Desiccant breathers

Desiccant breathers incorporate particulate filtering with silica gel (or similar hyper-hygroscopic media) chamber that absorbs the moisture in the air that is pumped into it. Some designs have the use of a color-indicating desiccant (orange to green and blue to pink), which visually signals that the media is full and needs to be replaced.

Certain desiccant breathers include the check valve so that the device only "breathes" during the intake stroke, which prolongs the life of the desiccant by avoiding exposure that is unnecessary during the exhaust.

outdoor equipment such as in coastal or high-humidity areas, mobile equipment that has wide temperature fluctuations (which can encourage condensation), and systems that use fluids that are especially vulnerable to water-borne contamination, including biodegradable or fire-resistant hydraulic fluids.

3. Combination desiccant/particulate breathers

They combine an efficient particle filter phase (often 3-micron or smaller) with a desiccant moisture removal stage within a single housing. They're the most popular option for high-value or critical systems in which both particulate and moisture control are essential for proportional valves and servo valves, for instance, when the tolerances for contamination are very restricted.

Wind turbines with hydraulic pitch, yaw, and tilt systems; mobile cranes; high-precision proportional valve circuits; and any other application where humidity and dust are simultaneously a concern.

4. Breathers for check-valve

Check-valve breathers employ the flapper or spring-loaded check valve that restricts the flow of air to a specific direction, or to open only after an established pressure threshold. This limits the amount of air (and consequently the load of contaminant) that is able to pass through the filter's media over the course of the equipment's operation and extends the element's or desiccant life.

They are often used in conjunction with desiccant media instead of being a separate particulate solution.

high-cycle-rate equipment in which a typical breather's medium would be saturated rapidly like press hydraulics or high-frequency testing equipment.

5. Cap breathers that are filtered (Basic/low-cost)

The most basic option is venting a cap that has the basic mesh filter or foam that has a minimal amount of filtration. These are mostly obsolete components used on older equipment. They are being increasingly retrofitted with breathers that are more efficient as reliability programs become more advanced.

equipment that is low-criticality, low-duty cycle, and in which the targets for fluid cleanliness are not too high.

Selecting the correct breather to suit your requirements

Many factors can influence the choice of a breather:

• Ambient environments: Dusty, outdoor or coastal environments require deiccant and combination unit. In clean indoor environments, you may require only normal particulate designs.
• Goal ISO 4406 cleanliness code: Systems using gear valves, such as proportional and servo, generally have target codes within the 16/14/11-18/16/13 range, which requires breather filtration that is 3 micron or less.
• duty cycle The equipment that is high cycle moves greater volumes of air through the breather each hour, arguing for check-valve designs or bigger-capacity components to prevent regular replacement.
• Type of fluid: Biodegradable and fire-resistant fluids tend to be more hygroscopic, or more susceptible to water pollution, which makes desiccant protection more essential.
• Reservoir dimensions and headspace: Larger tanks can move greater volumes of air per stroke and could require a breather with a higher flow to ensure that airflow is not restricted, which could cause cavitation at the inlet of the pump or buildup of pressure in the tank.

Industrial applications

Mobile devices (cranes excavators, cranes agricultural machinery, etc.): Constant exposure to temperature fluctuations, dust and outdoor humidity make desiccant breathers or combination breathers close to being required for maintaining the cleanliness of the fluid in the field.

Wind turbines Hydraulic systems for pitch or yaw are used within nacelles that are subject to condensation and temperature cycles at altitude. This makes desiccant breathers a standard procedure for these types of applications.

Molding injection and other stationary manufacturing hydraulics The cleaner indoor environment usually permit standard particulate air breathers, however, proportional valves with tighter tolerance are still a benefit of combinators.

Hydraulics in the water and marine equipment In high-humidity areas, the control of moisture a priority which is why desiccant breathers are often preferred with check valves that limit exposure.

Stamping and press hydraulics The high cycle rate encourages check-valve breathers, which limit the amount of media exposed per cycle, thus reducing the frequency of maintenance.

Best practices for maintenance

• Examine the desiccant color indicators at a regular interval (weekly up to monthly based on the environmental conditions) instead of waiting for an overhaul schedule.
• Replace the particulate element based on the differential in pressure, or even visible saturation. This is not only calendar time, which is especially important on equipment that is high-duty cycle.
• Adjust the capacity of the breather to the volume of the reservoir and cycle speed. An insufficiently sized breather may limit airflow to the point of causing pump cavitation or pressurization issues.
• Consider breather selection as a part of a larger method of controlling contamination, in conjunction with offline and return-line filtration, rather than as an add-on.

What is the micron rating that an air purifier filter for hydraulics have?

The majority of systems require breathers that are rated as or below the best filtering point within the circuit. Typically, this is 3-10 microns. However, 3 microns are increasingly commonplace in systems with the proportional and servo valves.

When should the desiccant air filters changed?

Replace or regenerate the desiccant medium in the event that the color indicator displays saturation. This can vary significantly by location, ranging from several weeks in coastal environments with humid climates, to months of dry indoor conditions.

Does a breather filter result in pump cavitation?

Yes. A blocked, oversized or tight breather may hinder airflow to the tank in the intake stroke, leading to a vacuum situation which suffocates the pump's inlet and increases the risk of cavitation.

Do all tanks that use hydraulics require a filter for a breather?

Pressurized, sealed reservoirs might not vent to the atmosphere and don't need an air hose, but the majority of vented reservoirs do.