Bigger Isn't Always Better

In filtration, traditional thinking holds that more filterequals better filtration. This simply isn’t true anymore. WhilePTFE and PVDF membranes have been the material of choice forchemical applications, there are a variety of alternativefiltration materials today, such as ultra high molecular weightpolyethylene (PE) and polysulfone (PS), which make different filtersizes and shapes possible.

Unlike PTFE membranes, which are stretched, these alternativematerials can be cast to create specific pore structures.Asymmetric cast membranes, for example, reduce flow resistance,allowing more capacity to be packed in a much smaller area thanwith traditional materials. In addition to reducing costs, thisresults in a smaller surface area, which inherently reduces thepotential for defects and extractables.

A 10-inch length asymmetric membrane filter cartridge canproduce the same flow rate as a PTFE (or PE) membrane filtercartridge that has as much as 8 sq ft more filter area. This areais equivalent to the surface area of the inside diameter of 50linear feet of three-quarter inch tubing.

When you count the added surface area of the downstream supportmaterial, you’re up to the equivalent of 100 linear feet of tubing,and if you have multiple filters in your process, you could easilyhave the equivalent of over a mile of three-quarter inch tubingsurface area that is in intimate contact with your process fluids.

Is this a problem? Hopefully not, but as processes become morestringent, it is the unobvious contamination sources that may beproblematic. So, remember, bigger isn’t always better.

Bigger Isn't AlwaysBetterBigger Isn't Always Better