“Breather and vent filter” is an umbrella term for various filter series that are used in a wide variety of applications. Their primary role is to compensate for atmospheric or process-related overpressure or underpressure in housings and tanks.
Breather and vent filters (as well as filler breathers) are key components in the following application areas, among others:
Hydraulic systems
Gear units
Crankcases
(Sealed) liquid tanks
They are also installed in other closed housings that are subject to temperature fluctuations or which contain liquids with fluctuating levels.
In a hydraulic reservoir, the breather and vent filter enables pressure equalization. This is necessary as significant level fluctuations and/or a build-up of under/overpressure may occur during operation of the hydraulic system. Since breather and vent filters allows air to flow through them on both sides (in both directions), they can relieve both underpressure and overpressure.
In addition, considerable over/underpressure can also occur inside liquid tanks or closed housings due to temperature fluctuations. These fluctuations can be caused by temperature changes in the ambient air and the process liquid. This will cause the air inside the tank/housing to expand or contract. It is essential to compensate for the resulting overpressure or underpressure. A correctly dimensioned breather and vent filter enables the system to “breathe”. In so doing, it equalizes any over/underpressure and thus reduces the stress on the housing, tank, or vessel.
Filter materials in breather and vent filters
The filter materials used in breather and vent filters range from steel mesh and polyurethane (for coarse to medium filtration) to filter paper/cellulose and glass fiber (for fine filtration). In hydraulic systems, the filter fineness should be at least equal to the degree of filtration in the hydraulic or fluid circuit.
Breather and vent filters containing a special filter material for fine filtration are available with either fixed filter stages or replaceable filter elements.
The versions with fixed filter stages are typically smaller and are suitable for lower flow rates and dust loads. These entire filters are replaced during routine maintenance or when the contamination (saturation) limit is reached. An exception to this is breather and vent filters containing a steel mesh filter material. These types can be washed out in conventional diesel fuel.
Breather and vent filters that contain a replaceable filter element are usually larger designs that are suitable for somewhat larger flow rates. In these models, only the filter elements are replaced during routine maintenance or when the saturation limit is reached.
Filler breathers
Filler breathers are a subgroup within the category of breather and vent filters. These filters are mostly used in tanks containing hydraulic fluid or other liquids.
Filler breathers usually include a filling sieve (which is installed directly in the filling hole of the liquid tank) as well as a filter head, which is mounted on this filling sieve. The filter head contains the filter material, for which various different options are available. An exception to this is our Filtrec series of FA3… filters, which include a screw-on element (spin-on) attached directly to the filling sieve by means of a flange. Within this FA3… series, filters with a fineness from 3 µm (for cellulose filter material) to 1 µm (for glass-fiber filter material) are available.
Before filling a hydraulic-fluid or liquid tank using a filler breather, the existing filter head or spin-on element is removed. Filling then takes place directly through the filling sieve, which, however, can only retain coarse impurities. Therefore, if you need to ensure that finer dirt particles do not enter the tank and are filtered out of the fluid during filling, a separate filling unit (a filling pump with a filter unit) should be used.
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