BS ISO 3968:2016 pdf download – Hydraulic fluid power — Filters — Evaluation of differential pressure versus flow 9 Procedure 9.1 Pipework correction In place of the filter under test, install a pipe with the same diameter as that of the test rig pipework. Determine the flow rate versus differential pressure characteristic curve of the measurement section between zero and the maximum flow rate scheduled for the testing of the filter in 0,2q R increments. The test fluid shall have the same viscosity as that used in 9.3, 9.4, 9.5 and 9.6. 9.2 Cleanliness of test circuit Install the housing of the filter under test without its filter element (6.1.3) or a head and its empty spin- on (without internal element, 6.1.1 – 6.1.2 and start the pump to obtain a flow rate of approximately the maximum flow rate scheduled for the test. Let the fluid circulate to allow the temperature to stabilize and until the required fluid cleanliness level is achieved. The fluid cleanliness level should be selected to suit the grade of filter tested and not to contribute to blockage. Bleed the circuit to eliminate any entrained air if required. When the required cleanliness level is achieved, report in the test report and if necessary bypass the clean-up filter. In the case of change of the test fluid, ensure that no residual fluid can mix with the new fluid, by completely flushing the test stand. 9.3 Characteristics of the filter housing (filter type 6.1.3) 9.3.1 Prior to determining the differential pressure of the filter housing without a filter element as a function of the flow rate, ensure that exclusion of the filter element does not cause any flow perturbation. If there is flow perturbation, replace the filter element with a substitute element that creates a flow path as identical as possible to that caused by the filter element. The section for passage through the substitute element shall be as large as possible to reduce pressure drop. Record in the test report the characteristics of the filter housing with the substitute element as those of the filter housing and identify that a substitute element was used. 9.3.2 If the filter housing is equipped with a bypass valve, immobilize it in the closed position during the test. 9.3.3 Adjust the test flow rate q V to 0,2q R . Record Δp and temperature. 9.3.4 Repeat these operations for increasing flow...

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