In many applications, post-filtration may be needed, especially if you’re trying to adhere to a stringent cleanliness requirement. In many cases, simply adding a HEPA afterfilter could get you where you need to be, but ultimately it will be subjective to the application.  In terms of an absolute guarantee on filter life, I would be a bit hesitant to guarantee a filter changing frequency, as it will depend on the individual application.  I would assume that whoever gave the "guaranteed" filter life must have thoroughly evaluated the project, measuring the amount of coolant being used, accounted for cycle times, calculated the concentration of fugitive mist, etc… Let’s say you have a leaky roof, and I provided a 5 gallon bucket - I can’t guarantee when you’ll have to dump the water out of that bucket, because I have no idea how much water is going to leak in - that’s probably not the best analogy, but you get the idea.   Most performance guarantees will have some stipulation, or the performance will be rated based on a controlled environment, as in a testing facility.  As testing procedures typically aren’t as intense as the actual operation, what looks good on paper may not necessarily apply out-of-the-box.

In my opinion, it would be most beneficial to address your machine tools with Electrostatic Pricipitators unless the application isn’t ESP-friendly. It’s no secret that there’s a considerable cost of ownership with media-based systems, and maintenance headaches with centrifugals, but they each have their own place in the machine shop. Of course, vendors who only carry centrifugals are invariably going to recommend centrifugals, and the same goes for the media vendors, and ESP vendors alike. On a personal note: being a provider of both media and electrostatic mist collectors, I would only use a media system if ABSOLUTELY necessary.  ESP units will require more frequent PM scheduling than media units due to frequent cleaning, but having additional electronic cells on-hand quickly addresses that issue.  The cost savings vs. having to constantly replace media filters in most cases makes it a no-brainer.  In one particular instance, I visited a plant where they were spending in excess of $40,000 a month in media filters!

 As for the average centrifugal unit, it’s not uncommon for the efficiency for finer mist to be lower, as its main function is to separate the heavier droplets.  The media filter is included to catch the finer mist, but doesn’t always do a fantastic job.  The balancing issues they have will invariably cause vibration issues, possibly leading to inaccuracies in part production.  Another gripe maintenance techs have voiced is the job of essentially rebuilding the units when they have to replace the bushings and bearings every few years or so.

It is very important that you make sure to do your homework before settling on any particular mist collector, as there are so many effective models out there.  If applied right, each of these units has its own place in the industry, but you want to ensure that you’re using the right tool for the right job. 

Any input would be appreciated.

Jason Wege