The Ultimate Guide to Dry-Out Filter Cartridges

Are you a professional dealing with transformers, circuit breakers, tap changers, and switchgears? Or maybe you’re simply someone who wants to understand more about the world of insulating oils? Either way, you’ve likely come across a vital component known as dry-out filter cartridges. These elements play a crucial role in ensuring the longevity and efficiency of the aforementioned devices. This article aims to provide an in-depth understanding of dry-out filter cartridges, their applications, features, and selection process.

What are Dry-Out Filter Cartridges?

Dry-out filter cartridges are essential components designed to remove carbon and moisture from transformer and insulating oils. They are manufactured from specially formulated medias that are layered with high-quality water absorptive medias and cellulose. Their availability in micron efficiencies ranges from 1µm down to 0.4µm, making them incredibly effective in their roles. These cartridges are primarily used on lower voltage transformers, circuit breakers, tap changers, and switch gears.

Applications of Dry-Out Filter Cartridges

The wide variety of uses for dry-out filter cartridges includes transformer oil, circuit breaker oil, tap changer oil, switchgear oil, and dielectric oil. The most popular and cost-effective for general field use are the 1/2, 0.5 Micron Cartridges. These cartridges have an increased carbon removal capacity and efficiency compared to the 1 micron design, making them a natural choice for circuit breakers, and similar devices. While their water capacity is reduced, they have proven more than adequate for most applications.

Then there are the 1 Micron Cartridges, which have maximum water capacity combined with moderate carbon removal capability. These cartridges are typically used where removing free and emulsified water is the primary concern.

The P3, 0.3 Micron Cartridges are a variation of the 1/2 micron design. They contain a thin layer of 0.3 micron rated filter media sandwiched behind the same high carbon capacity filter media used in the 1/2 micron cartridge. This combination of filter medias results in a cartridge with excellent carbon capacity, suitable for applications where extra fine filtration is required.

And lastly, we have the P4D, 0.4 Micron Cartridges which add dissolved water removing capability to the performance features. This results in lower total water concentrations as measured by ASTM D-1533 (Karl Fisher), and typically further improves D-1816 breakdown voltage (spherical, or “VDE”, electrodes). These cartridges have the greatest free and emulsified water removal capacity (over 800 ml), plus dissolved water removal capabilities. Carbon removal efficiency and capacity are also much greater than 1 micron rated cartridges.

Benefits of Using Dry-Out Filter Cartridges

There are several advantages to using dry-out filter cartridges. Primarily, they replace 12″ Diameter Disc Filters resulting in a significant cost savings of 35%+ with a Single Cartridge. They are also highly efficient in free and emulsified water removal, ensuring that your devices continue to work at their optimum capacity.

Contact Information

For more information about dry-out filter cartridges, or to discuss your specific needs, feel free to reach out to us. You can call us at

Fill out our contact form or send an email to We are located at 1 Chestnut Street, Nashua, NH 03060. Visit our website at to browse our range of products and services.

Cartridge Selection Table

Choosing the right dry-out filter cartridge demands a careful examination of your specific requirements. Stay tuned for our upcoming Cartridge Selection Table, a comprehensive guide to help you make the best choice for your specific needs.

Portable Transformer Oil Filter Cart (Doc) by Steve Cook