What are the basic criteria for flow rate selection when using HYDAC filter elements in hydraulic systems?

When selecting HYDAC filter elements for hydraulic systems, the core principles for flow rate sizing are as follows: the rated flow shall be no less than 1.2 times the system peak flow, pressure drop shall be strictly controlled, specifications shall fit installation positions, and corrections for fluid viscosity and operating conditions shall be taken into account. All four points are indispensable; otherwise, problems such as filter clogging, increased system energy consumption or component damage are likely to occur.

First, requirements for basic flow rate multiplier. HYDAC stipulates clearly that the rated flow of filter elements must be at least 1.2 times the maximum operating flow of the system. A multiplier of 1.5 is recommended for some high-pressure or continuous operation scenarios. For example, if the system peak flow is 50 L/min, the rated flow of the filter element shall be no less than 60 L/min. A 20% flow margin can cope with instantaneous flow fluctuations, changes in oil viscosity and flow reduction caused by filter clogging, and prevent frequent opening of the bypass valve which leads to filtration failure.

Second, pressure drop control serves as a key constraint. Excessively high flow or undersized filter elements will result in excessive pressure drop. The initial pressure drop of return line filter elements shall not exceed 0.35 MPa, while that of filter elements for high-pressure pipelines shall be below 2 MPa. The DF330 series is recommended for return flow exceeding 800 L/min to keep the pressure drop within 0.2 MPa. Excessively high pressure drop will increase the load on pumps, raise oil temperature, and even cause deformation or rupture of filter elements. On the contrary, an unnecessarily low pressure drop means over-specification of filters and waste of costs.

Third, select flow specifications according to installation positions. Suction line filters require large flow capacity and low pressure loss. Models such as 0030R and 0060R with a filtration precision of 80-150 μm are preferred, and filters without bypass valves are adopted to avoid pump cavitation. Filters for pressure lines are designed for high pressure; models like 0240D and 0330D are applicable, with flow rate matching the peak flow of the main circuit and pressure resistance no less than 42 MPa. Return line filters need to handle the largest flow. Models including 0660R and 1300R are widely used to balance high flow rate and low pressure drop.

Fourth, make corrections for viscosity and working conditions. The rated flow of HYDAC filter elements is calibrated at a standard viscosity of 32 mm²/s. The actual flow will decrease as fluid viscosity rises. The correction formula is: Actual Flow = Rated Flow × √(46 cSt / Actual Viscosity). Upsize flow specifications for working conditions with low temperature and high viscosity, while a slight downsize is acceptable for high temperature and low viscosity. For systems with variable frequency drives or impact loads, sizing shall be based on peak flow to prevent filter failure caused by dynamic flow impact.

In conclusion, flow rate selection for HYDAC filter elements shall be based on 1.2 times the peak flow, with strict pressure drop control, proper matching with installation positions and viscosity correction. This will ensure system cleanliness and filter service life, as well as reduce maintenance costs.