Pleated Filters vs. Bag Filters

Experience and common sense suggest the benefits of pleated filters vs. bag filters. Of course, there are pluses and minuses to any selection that must be weighed based on the circumstances.

The initial cost of a bag system is sometimes less than a cartridge filter system, and this is often attractive. Also, the ability to collect dirt on the inside of something is often attractive, vs. collecting dirt on the outside of something. Bag filters are sometimes the preferred route for many types of applications, including ones where 1) a short term view is more appropriate than a long term view, e.g., a temporary process 2) a batch process 3) relatively clean fluids 4) a strong preference for collecting debris on the inside vs. the outside 5) the contaminants form a very permeable cake that allows flow even when there is a thick build-up..

Unpleated bag filters very often have lower dirt holding capacity than a properly selected pleated filter cartridge, however. It is very common for a bag filter user to get tired of changing filters every few hours (or some inconvenient period of time) and ultimately retrofit the bags with “pleated bags” – a type of cartridge filter that flows from the inside to outside – and then get much more life and reduced change-out labor, and overall lower filter expenditures.

A fallacy is that bag filters in liquid service ought to “fill up” the way a vacuum cleaner bag can fill in air service. But bags in liquid service usually do not fill up at all, but plug up on the surface and/or in the depth of the bag’s filter medium, just like cartridge filters, and life can be cut short due to a lack of surface area. Please see the following illustrations that explain why 2x surface area can improve life up to 4x. In my experience, the 4x is not a theoretical upper limit or “asymptote” (like the speed of light or some unreachable star) but is something that is often actually achieved. For some strange reason – maybe experimental error or the like – life can sometimes “mysteriously” increase by more than 4x when doubling surface area. The general relationship between life increase (for a filter used to the point of plugging) and surface area increase is as follows:

(Surface Area Increase Multiple) < Life Increase Factor < (Surface Area Increase Multiple)^2

The slides below illustrate filter plugging and explain how increased surface area can provide a disproportionate filter life benefit.

Because no single filter type is automatically best for every application, Delta Pure filtration offers a variety of filter styles including melt blown filters, pleated filters, string wound filters, combination filters, and more. We also offer a variety of materials, including polypropylene, glass, PVDF, nylon, polyester, cotton, rayon, and more.

Contact Delta Pure Filtration to have us assist with increasing filter life or solving some other filtration challenge.