How Does a Hydraulic Filter Work?
How Does a Hydraulic Filter Work?
How Does a Hydraulic Filter Work?
Filters act like a screen. They hold solids from streams of liquids or gases. In the case of screens, a solid-free filtrate and a filter cake are produced from the solids captured.
However, the separation does not occur independently, but only as a result of the pressure difference in the transport medium upstream and downstream of the filter medium. For this pressure difference, the medium can be filtered with positive pressure or sucked through the filter with negative pressure. Likewise, hydrostatic pressure or centrifugal force drives a filtration.
Hydraulic filtration principles
In hydraulics, surface filtration and depth filtration are the most common.
Surface filtration filters have geometrically defined spaces; Particles separate at the surface. In case of very high accumulation of dirt, a filter cake forms on the filter (sieve), which acts as an additional filter as its thickness increases. This filter cake should be removed regularly to maintain control over the filtration process.
Depth filtration filters use non-woven fabrics with irregularly arranged fibers between which solid particles are deeply separated. It is not possible to clean the filter material (eg glass wool). Therefore, the filters should be replaced when they are completely dirty. Depth filtration is mainly used where only the fluid will be reused. Dirty filter parts are discarded.
The science behind filtering
For filtration, filter media with pores or pores smaller than the size of the particles to be separated is selected. Also, the inertia of the dirt particles in the fluid streams ensures their separation on the filter material. In the case of gases, electrostatics also support filtration. Nonwoven filters used for this purpose receive an electrical charge in all their fibers.
Various filter media
Non-woven fabrics made of cellulose, fiberglass or plastic are not only used for filtration of gases. They are used for filtration of liquids as well as for:
fabrics made of plastic or metal wires,
porous solids (mostly sintered metals) and
bulk materials.
In the future, nanofilters will provide even more refined filtration.
Often, modern filter materials are still chemically or physically treated to increase or optimize natural filter properties.
What filter media does ARGO-HYTOS use?
For example, in suction filters for tank installation, you will find a mesh made of tightly woven polyester wires. It has, for example, a mesh size of 135 micrometers or 0.135 millimeters.
Other filters such as ARGO-HYTOS backflow filters for sequential installation achieve even more. With multi-layer glass fiber mats, they retain even particles smaller than ten micrometers or 0.01 millimeters.
These two examples from the ARGO-HYTOS portfolio of hydraulic filtration technology show you the precision that is possible today – a portfolio that is constantly being further developed.
This is done, for example, with the EXAPOR ® MAX 3 filter elements, the successors of the successful EXAPOR ® MAX 2 model. The third generation of this filter design once again reduces pressure loss by up to 20 percent. It also has up to 15 percent more dirt holding capacity and many other benefits.
You can realize these benefits every day at your plant and your machines: higher machine availability, longer maintenance intervals and lower operating costs.
Important features of a filter
The quality or efficiency of a filter can be recognized by various specifications or features. These are briefly discussed below.
Filtration rate and separation efficiency:
The filtration coefficient ß is calculated as the ratio between the number of particles before the filter and the number of particles after the filter, similar to efficiency. Filtration efficiency processes the filtration rate to show as a percentage how efficiently a filter separates dirt particles from a liquid.
Dirt holding:
This property has two properties: the absolute dirt holding capacity in grams and the specific dirt holding capacity in milligrams per square centimeter. Both are only used in conjunction with depth filters.
Pressure drop:
When fluids flow through a filter, there is a regular pressure drop. There is an initial pressure drop for any filter that has not yet been used. The more dirt is trapped, the greater the pressure increase in the filter. This effect is also used by clogging indicators to indicate the best time for filter maintenance.
Cleaning:
The robust surface filters of ARGO-HYTOS can be cleaned up to 3 times. Depth filters, which are used for moderate dirt accumulation and pass through at nominal flow rate, can be used for at least 1000 operating hours. In principle, it is recommended to replace it once a year. By the way: 1000 operating hours corresponds to a distance of 60,000 km for a passenger car.
What hydraulic filtration technology does ARGO-HYTOS offer?
ARGO-HYTOS gear pumps for industrial and mobile hydraulics work with a variety of oils and lubricants. Even of optimum quality, new oils contain a lot of contaminants and should not be used unfiltered. The size of these dirt particles is usually in the range of only a few micrometers, making them invisible to the human eye. Still, this is enough to cause long-term damage to plant or machinery.
The first thing that happens next is the need for repairs and more frequent plant failures with expensive downtime. In general, the service life of the machines is reduced, resulting in higher costs. In contrast, the investment in a suitable filter system is marginal. ARGO HYTOS integrates suitable filters directly into their systems or machines. However, they also offer separate filters for installation or refresh on your systems.
Hydraulic Suction filters:
Suction filters are attached to tanks, a suction connection or directly to the suction line of the pumps. Suction filters fully protect these pumps from contaminants sucked from the tank. When planning a system, you should always consider how filters affect pump performance.
Suction filters are also not very suitable for fine filtration. In this case, they create too much negative pressure in the suction line.
Hydraulic Return filters:
ARGO-HYTOS return filters are available as on-tank filters, in-tank filters and in-line filters. It is recommended to use a return filter to clean the returning oil before it enters the tank. It is mounted directly on the tank or at the end of the return line.
Hydraulic Pressure filters:
You integrate pressure filters right after a pump in the pressure line. The filters then protect all downstream components. ARGO-HYTOS offers high pressure filters in addition to pressure filters up to an operating pressure of approximately 100 bar.
Off-Line Filters
Off-line units filter the pressurized liquid in a separate circuit. In this way, you relax the filters in the main stream. This allows you to run the entire system more efficiently.
What are the selection criteria for filter technology?
When choosing hydraulic filtration, it is very important to consider the following:
Filter fineness – obtained from the required oil cleaning,
Differential pressure or filtration stability,
Size/time and other mounting criteria,
In addition to media compatibility, viscosity,
design conditions and
hydraulic conditions.
Finally, check the operating conditions regularly and replace the filter element according to the manufacturer's specifications or at least annually. The cost of this will quickly pay off compared to the cost of defective equipment.