Description DeVilbiss PROV-27-K4 Pro Visor Face Mask Filter Element Set of 4 loose active carbon filter cartridges for the DEVILBISS Pro-Visor full face mask. Replace the filters as part of your routine maintenance schedule to adhere the class 3 certification. Set of 4 loose active carbon filter cartridges for the DEVILBISS Pro-Visor full face mask. Replace the filters as part of your routine maintenance schedule to adhere the class 3 certification. We recommend that the filter cartridges to replace at least 1 x per 3 months. This is depends on the number of hours of use. Supplied in a pack of 4 filters. Pack 4 filters