By Robert Connor Rojina and Richard Juskowiak, Donaldson Process Filtration
Replacing your process filters at the right time is a critical part of food and beverage safety and profitability. If you replace elements too late, you risk contamination from mold and bacterial build-up. If you replace them too early, you risk unnecessary downtime and expenses. The ideal schedule for filter changes will be specific to each facility.
A primitive maintenance schedule is one you base on predetermined calendar dates. By nature, it’s quite arbitrary. An optimized maintenance schedule, by contrast, is one you establish from the manufacturer’s recommendations paired with careful evaluation—either through differential pressure performance, element integrity testing, or both. This optimized schedule takes more time to set up, but the benefits are a safer and more cost-effective system.
Here are recommended steps in your filter evaluation and change-out scheduling process:
Follow the filter manufacturer’s recommendations as a baseline.
Because steam sterilizing is a high-temp process, it puts stress on the element and wears it out the media after a number of cycles. Filters come with replacement guidelines, usually based on average number of sterilization cycles a filter can tolerate. Most elements on the market allow for 80 to 90 steam sterilization cycles, although newer technology, such as LifeTec™ filters designed by Donaldson Co., allow for 100 cycles or more.
This recommended replacement schedule is a starting point, but your facility may put lesser or greater demands on a filter. That demand may also fluctuate with the seasons or your particular resources. Humid weather cycles, for example, may require heavier use of your cyclone separator and coalescing filters to control moisture in compressed air. Well water will place heavier demands on liquid pre-filters than municipal water.
Monitor differential pressure.
The first way to establish a more precise filter change-out schedule is to monitor differential pressure (DP). DP, measured in pounds per square inch (psi), is the difference in pressure upstream of the filter versus the pressure downstream. This pressure change will indicate the amount of flow restriction the filter is causing. As the differential pressure rises, the filter is reaching end of life. A large pressure drop downstream will alert you that it’s time to regenerate or replace filters—before they cause a costly shutdown. However, this method can be more difficult in plants with complex filtration systems.
The filter manufacturer may recommend a maximum pressure differential, but the decision may come down to economics. If a filter starts out with a differential pressure of 1 or 2 psi, you might delay its change until 10 psi. As the differential pressure increases, your pumps will have to work harder to make up the for the lost pressure at the filter and keep the process output consistent. This creates a trade-off between increased energy costs and the cost to change your filters. If filters remain unchanged, they will eventually become completely blocked with contaminant and could cause costly shutdowns of production.
Conduct integrity testing.
Another way to determine your level of demand on filters, is to test the filters for wear. If your air, water, or steam is more contaminated than average, testing might support replacement every four months rather than the recommended six, for example.
In a formal integrity test, the elements are placed in equipment that measures DP, efficiency (percent of capture), or both. Test methods vary for air, steam, and liquid filters. For liquid membrane filters, the most common method is applying pressurized air to a wetted membrane to see how readily a bubble forms on the opposite side (“bubble point value”). If you have multiple elements performing the same function in your process, you can test two or three to represent them all.
A customized plan should include how frequently to steam sterilize, as well. For example, if you use membrane elements at the end of a water-bottling process, you could integrity-test the filters at the end of a selected shift and extrapolate that data over weeks or months to approximate the right change-out interval. The benefit is clear: You have months to plan and stock your replacement filters, so when the day comes to make the switch you have the parts you need to keep your system running.
Conclusion
Knowing downtime costs for filter change-outs can help set up a strategic filter replacement schedule. Donaldson can help you conduct this evaluation, and develop a customized preventive maintenance strategy that minimizes downtime by improving filter performance. Our team also provides initial rounds of testing for new customers to help establish an appropriate replacement schedule.
For the full article, see our contribution to Plant Engineering, October 2017.
