Throughout the first three entries in this series we've discussed the difference in two filter element testing methods, ISO16889 and DFE. We've also illustrated how many elements fall short of their stated beta ratio under dynamic flow conditions. Today we'll wrap it up with simulated cold start tests.
DFE Multi-Pass: Cold Start Contamination Retention
Once the element has captured enough contaminant to reach approximately 90% of the terminal ΔP (dirty filter indicator setting), the main flow goes to zero and the injection system is turned off for a short dwell period. Then main flow goes to maximum element rated flow accompanied by real time particle count to measure retention efficiency of the contaminant loaded element. The dynamic duty cycle is repeated to further monitor the retention efficiency of the filter element after a restart.
Figure 7 shows the performance of an element that was subjected to the DFE restart test. During the restart, particle counts after the filter increased by a factor of 20 on the 6μ[c] channel, and the ISO Codes increased by 4 codes on the 4μ[c] and 6μ[c] channels. During the restart test, there is no contaminant being injected so any particles measured were released by the element or were already in the test loop. The temporary high contamination load in the fluid can pass through the sensitive components or bearings that the filter is charged with protecting if it can’t retain the dirt.
Figure 8 shows the performance of a Hy-Pro element. The unloading is evident in the DFE rated Hy-Pro element, but the effect is greatly reduced. The competitor element A3 (Figure 7) unloaded 84 times more particles 6μ[c] and larger than Hy-Pro, and 14 times more particles 4μ[c] and larger. The DFE rated Hy-Pro element had much higher retention efficiency than the filter designed and validated only to ISO16889 multi-pass.
DFE and ISO 16889 Multi-Pass Test Results Comparison
Figure 9 shows the performance of like elements produced by three different manufacturers that were tested to ISO 16889. The results were expressed as a time weighted beta ratio. Element B had a better capture efficiency than the Hy-Pro element in the constant flow test environment of ISO 16889. All of the elements tested were true to their Beta Ratio of β7[c] > 1000.
Figure 10 shows the time weighted performance of the like elements tested to DFE multi-pass to illustrate the performance differences between DFE and ISO16889.
In Figure 11 the particle counts taken during flow change have been isolated to measure efficiency during dynamic flow. Since the DFE test has shown that filter element performance is at its worst during flow changes, isolating those sequences can help predict performance in dynamic conditions, and it is with this graph that we see how overall filter performance changes. Element B had a beta ratio in excess of β7[c] > 2000 when tested to ISO16889 (Figure 9). However, Figure 11 shows the average beta ratio of Element B during variable flow to be β7[c] > 500. The Hy-Pro element beta ratio was in excess of β7[c] > 10,000, true to rating even in the dynamic test. The Hy-Pro performance in Figure 11 illustrates why Hy-Pro is committed to the DFE test method for design and development. DFE is Hy-Pro’s competitive advantage.
Relying solely on ISO16889 to predict how filter elements will perform in a dynamic system is like taking a boat into rough seas that has never been in the water. The current industry standard test for hydraulic and lube filter performance (ISO 16889) is a good tool for predicting performance of off-line filters and circulating systems, but it does not accurately represent the stress of a hydraulic circuit with dynamic flow conditions or a lube system cold start. Without DFE testing, it is difficult to truly predict actual filter performance in a dynamic system.