Reducing total filtration costs, increasing filtrate yield, and obtaining longer filter media life cycle all appear high on the filtration application and selection priority pyramid, second only to the cost of the vessel and media itself.

As if deciding which technology to use; bag filters opposed to cartridge filters isn’t difficult enough, many process and manufacturing engineering disciplines are faced with filtration systems providing high post installation media costs with elevated process interruptions for media change, and while these scenarios aren’t very attractive the vigilante group of operators responsible for changing media are always looking for the specifying engineer or vendor responsible. Fortunately, most manufacturing plants do not have trees with long sturdy limbs growing next to their filter systems.

Recently a R&D engineer on the lamb from the operator posse approached Fischer-Robertson, Hamilton OH, to help solve his "hot" varnish filtration issues. The vessel was a 7-round Size #2 25micron polyester bag filter installation polishing a varnish at an elevated temperature of 340oF The vessel(s) required change 89 times a month with an annual bag acquisition and disposal of 7500 bags.

While the client was up to date on the latest "cure what ales you" bag technologies being introduced by those fabulous marketing fellows, after much testing he was quick to realize that those fancy brochures and claims to fame were prepared by those less field application experienced.

Fischer-Robertson’s approach was rather simple, unfortunately for the client he was in that area where clarifying depth filtration is more appropriate, yet given the risk of an upset product cartridges would prove financially extreme.

It appeared the 25 micron bags would blind what one would consider somewhat rapidly. Short bag life cycle centered around debris load, more importantly, suspecions centered around broad particle debris size distribution. Appreciating the 25 micron bag was surface filtration available open area disappears quickly when addressed with 100-200 micron "skins".

Solutions weren’t attractive, these included added surface area devices, graded density bags, expanded area "pleated bags" etc., none a realistic problem solver.

Fischer-Robertson’s solution to the challenge, scalp (pre-filter) the varnish with a 100micron bag then polish with the 25micron, not with the purchase of a second 7-round bag vessel, rather simply use a 25micron polyester bag lined with a 100micron "scalping" bag. Upon hearing the $4.00 bag price, and short on alternatives Fischer-Robertson produced the bags, and testing proved without a doubt that fancy brochures aren’t as good at providing solutions as a talented, experienced process filter supplier.

Results breed success, upon completion of the 25micron bag effort the client tested the Fischer-Robertson produced "dual layer" bag on a second application, which also proved rewarding. Currently he enjoys the total cost of filtration reductions and yield increase for both his 25 & 50 micron bag filter requirements.

What many filtration media developers and marketing folks fail to realize is only a clients specific process fluid on a given day with a given debris load and characteristic will determine bag or cartridge life cycle, filtrate yield, pressure differential and their influence upon process flow.

The dual layer approach to this clients success can be contributed to identifying with the issues and taking a practical root cause approach to problem solving.

Obviously, the idea of putting bag in a bag is about as simple as it gets. In this case it didn’t take extensive R&D and media development, and the use of the latest in expensive bag filter technology. Sometimes simple is better, while sometimes unique media technologies are the answer. The key is to rotate the cube, take off the blinders, remove the marketing clutter, identify the issues and take the actions required to accomplish the task.