Catalogue 9 - STAUFF Filtration Technology

A 22 www.stauff.com/9/en/#22 Choice of Filters Choice of a Suitable Micron Rating Generally, the type of components incorporated in the hydraulic system will determine the micron rating required. It has been clearly demonstrated that system components will operate reliably for years if a specific minimum oil cleanliness grade is maintained. Frequently the choice will be determined by the most sensitive component in the system. a) Operating Filter To get a rough, first rating of what filter is needed to assure a certain oil cleanness grade please have a look at page 19. Apart from the specific flow rate (l/min per cm 2 of filter area), other factors such as operating environment and condition of seals and breathers can have an effect on the cleanliness grade which can actually be achieved. b) Protective Filter Occasionally, protective filters are fitted downstream of major components, e.g. the pump, to collect the debris in case of a catastrophic failure. This avoids total stripping and flushing of the system. For economic reasons, protective filters are normally one grade coarser than the operating filters since they do not significantly contribute to the cleaning of the system and this extends filter service intervals. Choice of the Optimum Filter In selecting the filter, the following information must be considered: Maximum flow volume (Q max ) through the filter including surge flows Kinematic viscosity ( υ ) of the fluid in mm 2 /s (cSt) at cold start temperature and operating temperature Density ρ of the fluid Micron rating (µm): see table on page 19 Filter material The aim is to choose a filter whose total differential pressure (∆p) is not higher than ∆p max = 1,0 bar (for Pressure Filters) or ∆p max = 0,5 bar (for Return-Line filters), in a clean state at the normal operating temperature. These values have been proven in practice to give the optimum service life for the element. The nominal flow volume of the filter is the obvious reference value for pre-selection and this should be larger than the flow to be filtered. Q nom > Q max Calculations based on the filter data will verify whether the pre-selected filter meets the requirements, at operating temperatures: ∆p max ≤ 1,0 bar (for Pressure Filter) ∆p max ≤ 0,5 bar (for Return-Line Filter) The total differential pressure of the assembly ∆p Assy is calculated by adding the differential pressure of the housing ∆p Hous and that of the element ∆p Elem . Both the kinematic viscosity and density of the operating medium should be considered for the selection, as the flow curves on the pages following have been determined with a kinematic viscosity of υ = 30 cSt and a density of ρ = 0,86 kg/dm 3 . The values of the pressure drops for the ∆p Hous and the ∆p Elem can be read from the flow curves on the pages following. The values for the kinematic viscosity in cSt and the density in kg/dm 3 should be inserted into the following formula: ∆p Assy = ρ ∙ ∆p Hous + ρ ∙ υ ∙ ∆p Elem 0,86 0,86 30 The filter size is suitable if the ∆p Assy < ∆p max . If the calculated ∆p Assy is higher than ∆p max select the next larger filter size and re-calculate until a satisfactory solution is found. The following two examples explain and help to understand the procedure of calculating a filter. Examples of Calculation Example 1: Selection Pressure Filter System Information: A Pressure Filter with an Inorganic Glass Fibre element is required immediately after the pump. The system has standard components and is operating at pressures up to 200 bar. The filter shall be fitted with a bypass valve and a visual clogging indicator. For better understanding only the calculation at the upper temperature is carried out. Data given: Q max : 100 l/min Oil type: ISO 68 Temperature max.: +50°C Viscosity υ operating : 44 mm²/s Density ρ : 0,882 kg/dm 3 Micron rating: 10 µm (see table on page 19) First Step Pre-selection of the size: SF-045, Q nominal = 160 l/min > Q max Pressure drop values (at viscosity of 30 mm 2 /s) from the flow characteristics: ∆p Hous = 0,15 bar (SF-045 ..., see page 40) ∆p Elem = 0,77 bar (SE-045-G -10- B/4, see page 40) Determination of the correction factor: ∆p Assy = 0,882 ∙ 0,15 bar + 0,882 ∙ 44 ∙ 0,77 bar 0,86 0,86 30 ∆p Assy = 1,31 bar ≥ ∆p max = 1,0 bar Since the actual pressure drop is larger than the allowed pressure drop, a larger filter has to be chosen. Second Step Selection of the next larger filter size: SF-070, Q nominal = 240 l/min > Q max ∆p Hous = 0,15 bar (SF-070 ..., see page 40) ∆p Elem = 0,45 bar (SE-070-G-10-B/4, see page 40) ∆p Assy = 0,882 ∙ 0,15 bar + 0,882 ∙ 44 ∙ 0,45 bar 0,86 0,86 30 ∆p Assy = 0,83 bar ≤ ∆p max = 1,0 bar In a clean state, this filter fulfills the requirements and is suitable for the application. The correct filter designation would be SF-070-G-10-B-T-G20-B-V . Catalogue 9 § Edition 02/2023 Filtration Guideline