The Future of Hydraulic Oil Filtration
Achieving proper cleanliness levels in today’s hydraulic systems requires the successful capture and removal of contaminants. Filtration must be done in a way that doesn’t disrupt the flow of oil, or unduly increase the pressure drop within the system. It’s a delicate balance between system design and efficiency.
The future of hydraulic filtration focuses on three major areas:
Developing finer fiber technology to be used in filter media,
Engineering the various layers/arrangements of filter media for maximum effect, and
Improving the overall construction and design of the filter to maximize the useful filtration area for optimal performance.
Manufacturing Efficiency Into Filters
One of the simplest forms of filter media is a sieve or strainer. Depth media, the popular choice for hydraulic filters, consists of random layers of fiber strands to create a multi-layered sieve. Depth filtration technology is designed to have higher efficiencies and hold more dirt than strainers.
Modern filter media design often interlaces layered combinations of coarse media with finer grades - with the idea that the larger dirt particles are captured on the surface, while the finer particles are trapped deeper within the media.
Improving efficiency through increased layers or finer pore sizes can have undesirable consequences. Both methods can lead to an increased differential pressure across the filter, which may shorten filter life and lead to an early filter change.
It’s unfortunate that many hydraulic system breathers consist of an open cover or tube, or at best a filler cap without a proper filter element inside. No unfiltered air should be allowed to enter a hydraulic system.
Wherever possible, oil reservoirs should have adequate breather filters installed; ambient air carries considerable quantities of contaminants.
A quality breather filter with an absolute efficiency of Beta 10µm(c) = 75 or better will suffice for most circumstances.
A quality 10µm liquid filter will typically be more efficient at capturing fine dirt particles when applied in air filtration applications. In humid conditions, breathers should remove water (desiccant).
Reservoirs and Drum Storage
Good reservoir design will ensure that any water or heavy dirt settles to a small area or standpipe at the base of the reservoir, which can be drained periodically. Water left in the oil leads to bacteria growth and chemical degradation.
Oil drums are best stored on their sides so that the bungholes are submerged. This prevents standing water or humidity drawn into the drum through breathing caused by temperature changes.
Good reservoir design will provide return line diffusers, adequate baffles and sufficient volume to settle out heavy dirt particles, water and any entrained air.
Oil should be regularly recycled or used to prevent long-term degradation.
Ideally, oil should be filtered going into and out of the reservoir.
Of course, the perfect filter and the perfect filter media will do wonders for the hydraulic system. But when it comes to achieving optimal cleanliness levels, one cannot rely on filter efficiency ratings alone.
As discussed in this article, several other factors can influence a system’s integrity. Proper handling and a solid system design go a long way toward solving dirty oil problems. Each situation is different. Climates, environments and cleanliness requirements vary and should be taken into consideration. However, a good fluid power distributor will be able to accurately diagnose systems and recommend which media choices, filter types and filter positioning are right for every application.