Media technology

A brief history of the filter media

Fluids have been filtered as long as anyone can remember. First, sediments were removed from fluids by precipitation or flushing. These processes require space and time, but are still used in systems engineering, bio-sewage technology and similar.
With industrialisation and the use of fluid carrier media for mechanical engineering processes, single-acting fabric filters made of metal or renewable raw materials were primarily used. To this day, filters may be equipped with metal screens or screens made of oil-based plastics for rough filtration and pre-filtration. These single-acting filters can normally be used several times. The dirt retained on the surface can be flushed out by cleaning processes.
Due to an anticipated shortage of resources, alternative single-acting filtration processes have been developed that are based only on the mechanical separation of dirt and fluid. For example, in the 1970s, hydro-cyclone filters were frequently used in tractors of the ZT series. However, they could not establish themselves permanently on the market. The physical, active principles for the mechanical separation of two phases during the degassing of highly dynamic hydraulic systems of today have experienced a renaissance.

At the start of industrialisation, technical plants were primarily operated with air and water and could thus be ""maintained"" by single-acting filtration or by the production of steam. By the use of the first control elements and carrier media based on mineral oil, the purity in the system needed to be improved significantly, to spare the assemblies and components integrated in the system. The first filtration media were used that were primarily made of renewable cellulose. These paper filtration media are still used today for fuel filtration, air filtration or related process filtration systems.

Due to the growing awareness for ecological topics, shortage of resources and energy efficiency, these carrier materials have been re-assessed in terms of energy efficiency. Cellulose paper impregnated with phenolic resin only provided limited support in particular with the differentiated cleanliness requirements in different technical systems.

At the start of the 1970s, initial filter materials were developed in such a way that the use of additional carrier materials or filler materials with a range of different permeability or porosity values represented a more effective filtration concept. The basic idea was to use glass rods with a very small diameter in the filter medium. In Thüringen in particular, it was a long-standing tradition to produce "angel hair or fairy hair" in the glass-making trade. In the 1930s, it became possible to produce glass fibres with a diameter of 10µm on an industrial scale from molten glass. The first micro-fine glass fibres were presented in the USA in 1944. These were used in the 1950s to create the first filtration media made completely of glass fibres. This was the birth of glass fibre materials. However, during the first years, glass fibre media impregnated with phenolic resin were difficult to pleat and had only limited technical characteristics. It was only when an acrylate binder was used that the efficiency of the glass fibre filter media could be improved.

In particular in the late 1990s, the focus of the oil filter manufacturers switched to alternative non-woven fabric filter materials, familiar from ventilation filtration and cigarette filter production.

Non-woven materials from chemical fibres made of natural polymers or of synthetic or mineral fibres are primarily used. The type of fibre used for the non-woven material is assessed and selected according to its chemical, thermal and physical textile characteristics for use in the customer application.

A special spinning method is applied to create a non-woven material from these fibres. This melt-blown procedure in combination with high-speed hot-air can be used to produce fine-grained materials with different structures and excellent quality. There is an extremely wide range of options for these melt-blown materials, which can be further processed without problems.

Melt-blown method

Additional filter media for various filtration tasks are:


  • Open-pore ceramic filters (filter chips) e.g. for soot particle filtration
  • Sintered stainless steel filter elements for e.g. oil retention and reducing the sound emissions at pneumatic actuators
  • Needle felt for large-scale industrial air filtration



Melt-blown method

Design of effective filter elements

A filter element mat for pressure or return line filter elements normally consists of:

  • Wire mesh fabric or elastomer fabric at the inflow end,
  • optionally with a protective layer at the inflow end,
  • optionally of a pre-filter material,
  • of a fine filtration material,
  • optionally with a protective layer at the outflow end,
  • optionally of an integrated drainage layer
  • and a wire mesh or elastomer fabric at the outflow end for support

Typical design of a filter element mat

Due to its many decades of experience, RT Filtertechnik GmbH as filter manufacturer always develops the optimum filtration concept for specific applications.

Your partner for energy efficient filtration

As the provider of energy efficient filter concepts for mobile hydraulic systems, it is our objective to offer our customers filtration solutions characterised by the use of flow-optimised materials or filter systems. A positive side effect is that our filtration solutions have enabled the reduction of the fuel costs for mobile hydraulic machines. The owners of machines can thus improve their efficiency and market capability.

Today, hydraulic systems are considered to be ecologically questionable, not only compared to systems driven by electric motors. The lifecycle assessment or CO2 balance is frequently distorted, depending on the perspective and system operation. RT Filtertechnik GmbH wants to use sustainable filtration solutions to show that a hydraulic system can also be a practical ecological alternative, in addition to the hard calculation facts. The user can use the fitting filtration option from the range of sustainable filter elements and detailed solutions as a series production solution and thus apply simple means to provide future generations with a clean environment.