Conflicting pressures on filtration systems

With increasing demands now being placed on production equipment to maximise productivity, cycle times are continually being reduced, while the intervals between maintenance activities are extended.

For equipment designers, these conditions present a difficult paradox. Higher pressures and faster movement increases the wear on components, but longer maintenance intervals reduce the opportunity to replace them before they break.

A longer life in tough conditions, therefore, requires strategies that reduce sources of unnecessary wear wherever possible. For fluid power equipment, reducing contamination in the system is the most important of these. Water, chemicals and particulates all take their toll on hydraulic and pneumatic systems - corroding parts, destroying lubricants and damaging bearing surfaces. Filtration limits this damage by capturing and containing contaminants before they reach critical components.

For demanding production environments, however, filtration presents a second paradox. Fast manufacturing calls for efficient, high-volume fluid flows, but filters impede that flow, reducing the fluid available to the application, or requiring larger pumps and increasing energy consumption.

In recent years component makers have battled to overcome these limitations with filter system designs that combine effectiveness in removing contaminants with high efficiency and a long service life.

With pneumatic equipment, for example, filters are now being designed to ensure that air moves as smoothly as possible, with the minimum of energy-sapping turbulence or dead zones in the flow.

As a result, the latest designs feature an optimised bend angle at the inlet, which feeds the incoming air via deflector vanes. The resulting turbulence-free air path can reduce flow resistance by up to 75%, depending on the pipe diameter.

Advanced distributor designs, meanwhile, can better manage flow into the depths of the filter element, to ensure that air is fed to the entire surface of the filter. Filter performance, however, can still vary dramatically over the lifetime of a filter. Some designs that offer good performance when new, degrade rapidly when exposed to the very contaminants they have been installed to stop.

Filter makers now employ nanotechnology manufacturing techniques to produce filter materials containing extremely thin fibres. These fibres can ensure that, while individual gaps between fibres are kept small enough to achieve the desired level of contamination removal, the total number of voids in the filter is big enough to minimise pressure loss.

Companies must also pay equal attention to other aspects of the system. Poorly selected or installed distribution pipework, for instance, can reduce system efficiency though leaks and by restricting fluid flow. Conversely, modern systems can combine turbulence-free flow, even in complex routes, with simple, reliable assembly and easy of maintenance.

Effective filtration is doubly important in hydraulic systems, where the closed nature of the circuit means that contamination can accumulate gradually over time.

It is, therefore, important to understand the degree and nature of contamination in the system, both to ensure that filter elements and hydraulic fluids are changed at appropriate intervals and because contamination can be an early indicator of wear or other problems in the system.

Traditionally, samples of hydraulic oils and lubricating fluids were analysed in a laboratory before contamination levels could be accurately measured, requiring time, money and resources; now this can be done quickly, easily and accurately at the point of use.

Handheld analysis devices, for example, will detect and measure the dielectric constant of a small sample of oil, highlighting changes in its condition brought about by the ingress of water, particle contamination, metallic content or oxidation.