What Are Filtration Specifications?
Understanding and comparing the performance of various hydraulic filters can be a complex task. In this article, we aim to clarify some terminologies for easier comprehension. Filter media, the materials used to capture particles from a fluid flow stream, must effectively catch particles while allowing fluid to flow through. The fluid's path through the maze of media fibers changes direction, resulting in cleaner fluid as it passes through the layers of fibers.
Filter media can capture particles through four mechanisms, often relying on a combination of these methods. Inertia works on large, heavy particles that continue in a straight line and collide with the media fibers due to their greater weight. Diffusion affects the smallest particles, allowing them to diffuse within the flow stream and collide with the fiber. Interception captures mid-sized particles that are not large enough for inertia but not small enough for diffusion. Sieving is common in hydraulic filtration, where particles too large to pass through the spaces between fibers are trapped.
Filter media can be made from different materials, and each type captures particulate contamination in various ways. Cellulose fibers, made of microscopic wood fibers bonded by resin, contain smaller pores and are suitable for petroleum-based fluids. Synthetic fibers, being man-made and smooth, provide low resistance to fluid flow, making them ideal for use with various fluids. Glass fibers in a matrix bonded with an epoxy-based resin system can offer high chemical resistance for hydraulic systems with specific needs. Wire mesh media, consisting of stainless steel or epoxy-coated wire mesh, is suitable for coarse filtration of larger particles.
When sizing the filter for system requirements, factors such as filter media, amount of contamination, flow rate, and fluid viscosity must be considered. Oversized filters can be expensive, requiring more system oil and costly replacement filters. To determine filter efficiency and dirt-holding capacity, filters must pass multi-pass tests per ISO 16889, an international standard. Particle counters are used to measure upstream and downstream particle counts, and beta ratios are calculated to indicate filtration efficiency. Filter manufacturers publish beta ratings to describe efficiency performance levels.
Ultimately, the effectiveness of a filter is demonstrated by how well it keeps fluid clean in real-world situations. Ensuring proper filters are used can be achieved through good analysis programs that inspect oil cleanliness. The beta ratio is a formula used to calculate filtration efficiency, and it is determined through multi-pass testing, measuring particle counts upstream and downstream of the test filter.
In conclusion, understanding filter media, efficiency, and sizing is essential for selecting appropriate hydraulic filters that meet the system's specific requirements and maintain optimal fluid cleanliness. Manufacturers' data and ISO standards provide valuable information to aid in making informed decisions regarding filter selection and performance evaluation.
