Improved efficiency thanks to intelligent filter systems
	Mobile machinery nowadays is virtually unthinkable without a hydraulic system. All kinds of machines - whether in agriculture, transport, construction or logistics – are equipped with hydraulic functions. These functions, such as lifting and lowering loads, driving rotary movements or even providing motive power, serve to boost machine productivity. This is why it is so important for the hydraulic system to be as reliable, efficient and maintenance-free as possible. Components of all modern hydraulic systems are produced by precision techniques. That means fitting tolerances well below 30 µm. The finest tolerances are applied to the most important – and most expensive – components, such as the pump, directional control valve or cylinder. Failures consequently present a serious problem, as troubleshooting is often difficult on building sites where there is no ready stock of spare parts. As with so many things, the rule here is “prevention is better than cure“! It is often said of hydraulic systems that “the components should be produced in the operating theatre and the system assembled in the delivery room“. Clearly, such meticulousness is not economically viable, and we have to recognise that the hydraulic system is subject to “attack“ from a whole range of dirt particles. However, the days when we used to accept this fact are long gone! In terms of contamination, a distinction is made between so-called primary contamination and secondary contamination. The former are so to speak inherent in the system and can be reduced by suitable measures. These impurities are also the main causes of long-term wearing processes. Secondary impurities means the dirt which penetrates from outside and therefore depends largely on the conditions in which the machine is operated. In order to guarantee the necessary protection of the machine, we need to use high-quality filter systems capable of withstanding the conditions of mobile hydraulic applications. RT-Filtertechnik GmbH proposes two solutions which have already proven their worth in numerous practical applications. It is natural for the customer to want to keep machine maintenance down to a minimum. To do this, he needs an economic filtration system. The best systems have proved to be those which provide full-flow filtration in the return line, with adapted “police filters“ at vulnerable points. As hydraulic tanks become increasingly compact, the less room there is left for the filter. The RME series by RT-Filtertechnik offers an optimal solution for a wide range of sizes. This series is integrated directly into the tank, thus removing the need for external attachments, e.g. filter head or feed line. The oil feed takes place inside the tank, which greatly stabilises the flow in the inlet section of the filter element. At this point, a typical RT magnetic pre-filtration system can be introduced. This effectively reduces the amount of micro-particles ranging from below 20 µm to 0.1 µm. By way of comparison: the diameter of a human hair is approx. 50-70 µm, and the scale of human vision ends at 40 µm. The compact design of the RME filters allows the effective filtration area to be maximised, resulting in optimal flow properties and a high dirt holding capacity. This guarantees an economic filter lifetime in all types of machine. This type of return-flow filter is typically used in excavators, concrete pumps, mobile cranes and transport vehicles with large-scale hydraulic systems. The major advantage of these filters from the machine manufacturer’s point of view is that it allows an entire series to be covered by different sizes. The user for his part can select the right filter element for his particular purpose, e.g. hammer applications, scrap yards, building sites, airports or road works, in order to optimise lifetime and efficiency. Various systems common in mobile hydraulics have what are known as closed circuits. The closed circuit is generally only part of the overall system and is supplied from the common hydraulic tank. Due to the nature of their function, the components in the closed circuit are particularly sensitive, which means that a full-flow return filtration supplemented by a police filter is not enough. In this case the pumps have to be protected directly at the inlet, i.e. in the suction line. Traditionally, this function has been – and still is - performed by suction filters. Most users are only too familiar with the creaking of pumps in wheel loaders and similar apparatus, especially during the winter months. This is due to the cavitation which may be caused by the use of undersized or inadequately maintained suction filters. Such a condition also restricts the functionality of the machine, as closed circuits tend to be used in hydrostatic travelling gears. In response to growing calls for compact, lighter components and tanks, the “classical” function of a hydraulic tank in mobile hydraulic systems fell victim to rational design: from this point of view a large hydraulic tank means unnecessary ballast, and the larger the oil volume the higher the cost. Thus began a steady trend towards smaller tanks which still persists today. As a logical consequence of this trend, attention began to focus on filtration – if only because of the limited space available. The idea of combining the return-flow with the suction filtration, which was heralded as a great innovation, would never have occurred to anyone 20 years previously. Now the possibility of improving hydraulic characteristics in critical states became a major preoccupation. RT-Filtertechnik developed such a filter system at an early stage and was thus able to gain considerable experience. The basic principle of these filters is based on full-flow return filtration. In this case the oil is not allowed to flow freely into the tank, however, but remains inside the closed filter container. From here, the minutely filtered oil is then fed to the feed pump via the suction line. The surplus can flow back into the tank through the so-called precharge valve. A certain surplus is in fact necessary for continuous operation, as it allows a pre-charge pressure to build up. The success and advantages of the filter are due to the following facts: One filter does the job of two (return-flow and suction). The feed pump is supplied with extremely finely filtered oil. The suction lines are pre-charged with excess pressure and the pump is filled. The benefit of the first point is clear: though relatively expensive, the single filter is cheaper overall than the two it replaces. Not only is the outlay in terms of design, purchasing and production much lower, but maintenance is more economical as the element costs no more than a high-quality return-flow filter element. The second point has the advantage of increasing both the functional reliability and lifetime of sensitive components. The third point increases the functionality of the machine from the user’s point of view. That means that the closed circuit (travelling gear) is reliably supplied even under adverse conditions such as prolonged periods of cold weather. This removes the need for long warm-up intervals and prevents lifetime-reducing effects such as cavitation. Such filter systems are already used in wheel loaders, fork lift trucks, municipal vehicles and airport logistics (container transporters, towing vehicles). They are also suitable for use wherever sensitive components need protecting directly in the suction line, e.g. rotary drives for mobile cranes. In the trade press, RT-Filtertechnik has already advised against buying suction-return flow filter systems such as these “off the peg”: fine adjustments are necessary to ensure that conditions remain optimal in all states of the system. To this end, RT offers a full measuring inspection as part of the product start-up process. This inspection quickly shows up any hidden malfunctions or interpretation errors. Even existing machines with double filtration can sometimes be converted, although once again, it is essential to obtain detailed advice first. Both filter systems described here can be used with different filter elements in order to achieve an optimal result. Whichever filter system you use, your choice should not be based purely on mesh sizes, impressive beta-values or other stated performance parameters. Although these values do help to classify the efficiency of the filters to a certain extent, the number-one rule of mobile hydraulics is that the filtration result can only be determined in the machine. Regular oil inspections are offered by independent laboratories or the RT filter service. This gives you permanent control over the filtration result while enabling you to optimise the lifetime of the oil. Investing in a well-adapted filtration system, original spare parts and good service is therefore well worthwhile for the peace of mind it brings.