You are seeking replacement filters for an established process. This could be due to technical issues with your current supplier, supply chain challenges such as extended lead times or stockouts, or the desire to find a more cost-effective option to reduce overall filtration expense. Regardless of the reason, it is crucial to have all the necessary information to provide to a potential alternate supplier.
We have seen numerous instances where customers utilize a filter of a specific pore size and subsequently contact us to order a similar filter with the same pore size, often without fully considering all relevant factors. This practice can result in unforeseen alterations to the filtration process, frequently with adverse consequences.
Different suppliers rate their filters differently. While all filters have a pore size rating, which indicates the particle size they are designed to capture, filter efficiencies, the fraction of that particle size that the filter will remove, can vary. This is particularly true of depth filters used in prefiltration and clarification applications. A conscientious supplier will provide both pore size rating and efficiency when discussing filter options. This allows for accurate comparisons to determine the specific needs of the customer. A filter rated at 0.45 micron with 95% efficiency will perform significantly differently than one rated at only 60% efficiency.
When comparing efficiencies, it is crucial to comprehend how the vendor is defining it. A 90% efficiency indicates that the filter is anticipated to eliminate 90% of particles at the specified pore size. Another method of characterizing filters is through the beta ratio (β-ratio). This is defined as the concentration of particles in the feed divided by the concentration in the filtrate. A 90% efficient filter would have a β-ratio of 10 (100 particles in ÷ 10 particles out). A 99% efficient filter would be classified as β-100 (100 particles in ÷ 1 particle out), and so on.
Some suppliers provide depth filters with absolute removal ratings, typically defining this as greater than 99.99%. However, some suppliers may claim a higher efficiency at larger particle sizes, even if the filter’s rating for a specific particle size is lower. For instance, a filter rated at 90% for 0.2 microns should have a higher removal rate at 5 microns.
It is important to note that a 5-micron absolute-rated depth filter may be virtually identical to a different supplier’s 0.45-micron filter rated for 90% efficiency. Similarly, the second supplier’s 5-micron filter at 90% is likely more porous than the 5-micron absolute filter you may already be using.
Switching to the second 5-micron filter without understanding these differences can result in significantly different performance. The second filter may allow a higher percentage of particles to pass through, potentially leading to premature fouling of downstream filters. Conversely, switching in the opposite direction would maintain protection of downstream filters but could result in higher pressure drop and possible premature fouling of the prefilter.
Comparing Depth Filters Between Vendors
| Vendor | Filter | Rating | Use | Description | Cost |
| Critical Process Filtration | 1 micron Polypropylene Depth | Nominal > 99%(β-100) | Water Filtration |
Excellent Performance Economical Pricing |
$$ |
| Vendor B | Nominal > 70%(β-3.3) |
Possibly Better Flow Less Particle Retention Reduced Downstream Protection |
$ | ||
| Vendor C | Absolute > 99.98% (β-5,000) |
Lower Flow Reduced Capacity More Frequent Changes |
$$$ |
We are also observing that this potential pitfall is not exclusive to depth filters. There have been instances where customers are seeking to replace membrane filters with identical specifications, such as the same membrane material and pore size, without fully comprehending their current usage. For instance, a potential customer ordered a 0.22 micron PES filter based only on the supplemental ordering material provided on a vendor's website. However, after installation, they noticed a decrease in process flow and a reduction in filter lifespan. It was discovered that the filter they were using was marketed as a 0.22 micron PES but was not characterized as an absolute filter. In reality, they had a 0.45 micron filter masquerading as a 0.22 micron filter. Since their application did not require sterile filtration, this discrepancy did not pose a significant issue. This situation can lead to engaging discussions between the vendor and the potential customer. The customer insists on obtaining a 0.22 micron filter, even if it is not the actual filter they are using, as per their process validation requirements. Consequently, the vendor must determine how to offer a “0.22 micron filter” that effectively meets the customer’s needs.
End users need to be knowledgeable about this, as this can result in unforeseen alterations in process performance if the replacement is not accurately identified. Additionally, it is crucial not to solely rely on the filter price. What may appear to be an effortless cost-saving opportunity could potentially escalate if more expensive downstream filters begin fouling prematurely.
None of this implies that the customer is unaware of the specific filter that is being used. Suppliers may intentionally or unintentionally make it challenging for customers to select the appropriate filter. While selecting a filter based on performance is always preferable, it is equally crucial to properly document the filter choice. Labeling a filter as “1 micron polypropylene” in the process documentation may not provide sufficient information for the next person to identify potential replacements.
In essence, when seeking a potential replacement filter for an existing application, it is imperative to furnish the prospective vendor with comprehensive information, including:
In most instances, CPF Applications Engineers can recommend the most suitable replacement filter based on the data provided. If certain information is missing, it may be beneficial to provide a sample of the filter currently in use for comparative testing. If necessary, CPF can conduct testing in our Applications Lab using fluid samples submitted by the customer to further optimize potential replacement filter options.
Are you in need of a replacement filter?
Critical Process Filtration supplies a wide range of filter materials and configurations. Our Applications Engineers can help streamline your selection process to make sure you get the right filter at a cost-effective price. For more information, please contact the Critical Process Filtration Technical Service team at Technicalservices@criticalprocess.com.