Yeah, I used to design purged and pressurized motor boxes for hazardous locations.

Consult a HVAC expert for the blower specifications.

Since you are only doing this to prevent dust from getting in, you don't have to worry about "turnover". All you need is positive pressure.

If you do have to "Purge" then you need turnover, and stagnet air needs to be controlled with flow measurement.

Charlie
www.facsco.com

You need to involve an engineer with more experience in this matter. Lint is usually considered EXPLOSIVE, you should be using what are called NEMA 9 enclosures! This is a very serious matter, not to be taken lightly. If not using NEMA 9 rated enclosures, you can use what are called "Purged Air Systems", but they are very specific as to how they operate and interlock with enclosure doors etc. they typically use dry, oil free instrument quality compressed air. Using fans may actually increase your problems by introducing air movement that can have a cooling effect, which may lead to condensation, then flashover etc. etc.

Please don't take this wrong, but your management needs to be aware that this is not something to assign to someone with no experience in this.

I am familiar with Nema 9.  I have used them in similar applications before, when I built equipment.  I understand where you are coming from.

My follow up question is this.....

These machines are from a major manufacturer, who does this all day long.  The plant only runs synthetic fiber (yes they will conduct some current, so shorting is an issue, but not combustion.  Would this still require redoing all of the cabinets?  I am a bit skeptical that the textile machinery company would have installed the wrong type of cabinet, if it is, in fact, required by law.  

Thank you for your post, and I dont mean to sound skeptical, but if you are in fact correct, then I need to know how hard I have to push back.

Classification of the hazard in an area is done by the Authority having Jurisdiction (AHJ), so they will be the ultimate authority. It could be, however, that this manufacturer knows that the synthetic you are describing is not in fact going to be classified as explosive. I would start with your AHJ though, because if that mfr is wrong and the AHJ says he feels it is a classified environment, you still have to deal with the consequences. My experience is that equipment manufacturers hold no sway over an AHJ's decision.

If it's a hazardous material it should be listed on a flamability classification chart.  I use to have a nice one, I think it was MTL Instruments that published it.  In fact I think it may have been a PDF you could get from their website.  My work with hazardous areas was primarily for solvents, so keep that in mind.

As for sizing the blower, this is something you can do it you want to make the effort.  There are tables for calculating pressure drops for various pipe sizes and lengths, number of elbows, etc.  It would also be a good idea to install gate valves (or other) in each line so you can balance the system.  You may also need to restrict the exhaust from the enclosures as well, which may get tricky depending on number of vents, size, conduits, etc.  Keep in mind that depending on the enclosure size, you could easily create a hazard by over pressurizing.  Get some DP gauges to install in each enclosure, I think Dwyer Magnehelics are only about $60-$70.

Good luck.