Filtration quality is the single most important measure of hydraulic machine health. More hydraulic failures are a result of particle contamination casued.
Highly viscous oil creates more backpressure than does thin oil, and you should consider how oil viscosity will vary with extreme changes in ambient temperature. Obviously, cold oil is thicker, and a marginally sized filter will bypass until the fluid reaches operating temperature.
Pressure drop is the pressure developed by the friction of the fluid against and through the material of the filter assembly itself, because the majority of filters are installed with a bypass valve designed to open by the backpressure created by the clogged element. Filter assemblies are often sized larger than required to prevent excessive pressure drop. An oversized assembly ensures little energy is lost to pressure drop, and as a corollary, larger filter elements are capable of holding more dirt before they become clogged. By sizing a filter intelligently, pressure drop is created only as the element becomes clogged with particles, preventing premature bypass.
Filter media quality plays a part in sizing assemblies, because finer filtration (i.e., lower micron rating), is more restrictive to flow because of the smaller gaps in the media, which are required to trap smaller particles. Also, the quality of the filter media plays a part because premium synthetic depth-media has a higher dirt holding capacity and will take longer to clog than cheap paper or cellulose media. If you are unsure of the variables when you are applying or purchasing a new filter assembly, it is advised to oversize the element and to use a high-quality medium.
When evaluating the performance of hydraulic filter elements, the most important parameters to consider are:
(1)Efficiency/ filtration ratio, expressed by “Beta” (ß)
(2)Dirt holding capacity (DHC)
(3) Beta stability
(4) Pressure drop vs. flow (Δp)
When selecting a filter element for your system, be sure to consider all four of these performance criteria. If an element is strong in three areas, but weak in another, it may not be the right choice.