Hiya Trilobite,
I'm not out to sell Nilfisk. I don't get paid for that job but I am familiar with some of their product and I know the blue filter you speak of. It was standard on the domestic/commercial motor used singly in the GM 80, GM 90 and Nilfisk double and triple motor machines (models numbers are not immediately at my recall).
If the motor(s) was/were running so hot as to damage or deform the blue filter you're speaking of that is a clear indication that the primary and/or motor filters were in need of cleaning or replacement. As I'm sure you know by now from many posters here, just emptying a vacuum cleaner is not enough. There are additional maintenance issues that have to be observed to keep any vacuum running optimally.
Those issues are often overlooked by staff just out to do a job and get paid. To go the extra mile you either have to have very enthused staff or Simon Legree heading management.
Before I switched to the HEPA I had that same blue filter on my Nilfisk GM 80 and 90. It was also backed up by a thick felt pad with an outlet for exhaust air that held it up against the plastic grill used to keep it in place. The merit for Nilfisk in this case has to be its use of motors made to take abuse. In similar circumstances, many other motors would have burned out in a heartbeat.
During my time of use fo mine I did make sure that the primary filter plus the high filtration motor filter I bought as an option were clean and not in need of replacement.
The multiple motor system is still in use by Nilfisk though the design of its machines has changed. As opposed to motors that rely on cooling from air used for dust and debris pick-up, new models use bypass motors (electric vacuum motors that indepently cool themselves). However, even though suction is not relied upon for cooling, larger diameter hoses and wands are necessary by way of the basic nature of the general work at hand. Nonetheless, for those who want them, Nilfisk has always supplied a good number of tools for special tasks like cleaning overheard pipe and conduits. I can't say that those kind of tasks will ever lead to "fun" vacuuming but then again -- it's work isn't it?
I've attached links to show what Nilfisk is doing now:
http://www.nilfiskcfm.com/ProductLit/CFM127.PDF
