Understanding air filtration

Published:  07 October, 2007

With an estimated 90% of pneumatic system failures attributed to contaminated air supplies, the need for a consistently high quality supply of compressed air is clear. However, air filtration and regulation systems are often incorrectly specified through a misunderstanding of both from where problems can arise and the functionality of the solutions on offer. To avoid these problems it is useful to look at the basics of air contamination and filtration so that an effective solution can be chosen.

The contaminants that commonly find their way into compressed air systems include particulate matter, moisture and oil, either from the environment surrounding the equipment or directly from the compressor. Despite significant improvements over the last decade, factories typically remain dusty and full of potential contaminants, which when compressed in air streams can cause serious problems.

If combined with moisture or lubricants, particulate contamination can lead to wear and even failure in pneumatic valves and other components. Moisture is typically introduced into pneumatic systems as water vapour in compressed air streams, which cools as it comes into contact with downstream equipment and remains suspended in the air flow where it cannot be drained away easily. It then has the capacity to break down lubricating oils, leading to increased friction between components and eventually failure.

A further contaminant that commonly causes problems in pneumatic systems is compressor oil. Initially emitted in vapour form, the oil condenses inside valves, cylinders and other components, where it collects dirt and damages seals. This can lead to both sticking in valves and further ingress of contamination; in both cases resulting in impaired system performance. It is worth noting that in many factory environments chemical substances can also be drawn into the compressor, attacking seals and gaskets and causing corrosion in air lines.

To protect pneumatic systems and components against these forms of contamination, a combination of filtration, drying and pressure regulation technology can be installed, depending on the requirements of the specific application.

Filtration can be achieved by installing a separator unit, which operates by directing the air flow over a deflector plate, creating a vortex that spins particulate and moisture contamination out of the air stream. The contaminants are collected at the base of the filter and are drained away.

While separators are typically effective in removing larger particles, they are generally incapable of removing particles below 0.5 micron, such as oil mist. To eliminate this level of contamination, coalescing filters can be used, which incorporate a number of elements through which the air flow passes, while the contaminants adhere to the filter media. This makes it possible to remove particles as small as 0.01 micron in size, which account for the vast majority of all contaminants.

It is important that both separators and filters are sized correctly, to offer effective protection for pneumatic systems. The required size of these components depends on the maximum flow of compressed air needed to power the downstream components and the maximum acceptable pressure drop across the system. While separators typically require a relatively substantial pressure drop to operate effectively, coalescing filters generally work more efficiently if the pressure drop is minimised, resulting in components with a large surface area to remove as many contaminants as possible. To remain effective, these filter elements require regular checking and replacement, as built up contaminants can increase the pressure drop and reduce the performance of the filter.

In addition to these filters, aftercoolers are also incorporated to remove much of the condensate in the air flow by reducing the temperature of the air coming out of the compressor. If further dehydration is required, absorption, adsorption or refrigeration dryers can also be used.

Just as important as effective filtration is pressure regulation; excessive pressure leads to unnecessarily high energy costs, while low pressure may be unable to support the loads present downstream. Therefore, pressure regulators are generally used to control output pressures using a piston or diaphragm acting against a spring. It is important to consider both the peak and average demand when determining the required pressure for an application, as, typically, only a proportion of the total number of devices in the system will be in operation at any one time.

Finally, adequate lubrication is essential to ensure pneumatic components are able to operate effectively and reliably over long operating lives. This is achieved by adding lubricating oil to the compressed air upstream of the components requiring the lubrication. Although increasingly modern components are designed to operate lube-free, therefore, eliminating the need for the lubricator, once lubrication is added to a system it must be maintained as lubricants can often wash away built-in pre lube.

The latest generation of filtration solutions now enable these individual functions to be combined in one modular system, making building and installing an effective filtration solution simple.


Easy connection

For example, John Hill, marketing services manager for Parker Hannifin's Pneumatics Division, says Parker Hannifin"s series of Moduflex FRL air preparation units includes filters, regulators, lubricators and other components that can be easily connected together to provide protection for pneumatic systems in a wide range of applications.

The units use patented Cliplok connectors, which allow each module simply to be slid into place and then locked securely in position using a robust and integrated clamp or over-strap. This unique method of construction enables a complete FRL assembly to be constructed in less than half the time taken for conventional devices.

Furthermore, the units can be built by an engineer or technician without the need for tools or special training. In addition, the clip together assembly method eliminates the need for extra parts such as pipe connectors and allows individual modules to be removed or changed quickly and easily, so that system maintenance and downtime can be reduced to a minimum.

The quick-release one-piece body design of this latest technology enables filter elements to be changed extremely quickly, ensuring that downstream pneumatic systems are maintained at optimum efficiency. This eliminates the problems encountered with some traditional systems, where elements are left unchanged due to the difficulty of the process, resulting in impaired system performance.

These robust aluminium filtration systems make choosing the right filtration solution for a specific pneumatic application simpler than ever before, as a bespoke set of individual components can be connected together in each case. With pressure levels carefully regulated and maintained throughout the system, contaminants can be removed effectively, while the necessary pressure reaches the downstream components.

With incorrect specification of filtration solutions a major factor in the failure of pneumatic applications, choosing a system that is simple to install and maintain can have a considerable impact on maintenance requirements and uptime. With increasing pressure to improve the efficiency of pneumatic systems and minimise energy requirements, the latest modular systems are offering system designers an invaluable method of achieving these aims, protecting equipment from contamination and, therefore, ensuring performance and profitability as a result.

For further information please visit: www.parker.com

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