BS ISO 3968:2016 pdf download – Hydraulic fluid power — Filters — Evaluation of differential pressure versus flow
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 rate values corresponding to increments of 0,2q R up to 1,2q R . Repeat the procedure for decreasing values of q V .
9.3.5 For each flow rate increment, calculate and record the differential pressure of the filter housing, as well as the end of test temperature, and calculate the average of the ascending and descending sets of results. 9.3.6 In order to obtain the characteristic curve of the housing only, subtract the pipework correction values measured in 9.1 from the averaged values calculated in 9.3.5.
9.4 Characteristics of the filter assembly (filter type 6.1.3)
9.4.1 Verify that the required cleanliness level is achieved and that the bypass valve is blocked before installing the element into the test housing.
9.4.2 Initiate the flow at its lowest flow rate to evacuate the air from the filter housing and circuit.
9.4.3 Repeat 9.3.3 to 9.3.5 taking care to use the same flow rate increments.
9.4.4 If required, repeat the tests in 9.4.3 with the complete filter equipped with its bypass free to operate.
9.5 Characteristics of the filter element only (filter type 6.1.3) Calculate the differential pressure generated by the filter element only by deducting the values obtained with the housing (9.3.5) from those measured on the filter housing together with its filter element (9.4).
9.6 Characteristics of the head and spin-on (filter type 6.1.2)
9.6.1 Verify that the required cleanliness level is achieved and that the bypass valve is blocked before installing the head and spin-on on the circuit.
9.6.2 Initiate the flow at its lowest flow rate to evacuate the air from the filter and circuit.
9.6.3 Repeat 9.3.3 to 9.3.4 taking care to use the same flow rate increments.
9.6.4 For each flow rate increment, calculate and record the differential pressure of the filter, as well as the end of test temperature, and calculate the average of the ascending and descending sets of results.
9.6.5 If required, repeat the tests in 9.6.3 with the complete filter equipped with its bypass free to operate.