joema2 wrote in post #16201160
The Rocket Blower has an internal intake filter and check valve. Air is filtered as it's drawn in the rear. When you squeeze it, the rear check valve closes and the filtered air is blown out the nozzle.
There is no check valve on the nozzle, so in theory some non-filtered air could be sucked in there, but due to the larger size and much lower restriction, most of the air is pulled in from the rear and is filtered.
If you're fanatical I suppose you could put your finger over the nozzle when releasing the body, which would insure that no unfiltered air (however tiny) is pulled in the nozzle. In actuality I don't think it's a problem.
The rocket blower is much safer than canned compressed "dust off" products.
There is absolutely no filter in either my Rocket Blowers. At the rear is simply a rubber flap-type check valve.
In addition, the nozzle does not present much resistance to air entering the bulb when releasing pressure on the bulb. I have not measured the flow, but sound tells me that about as much air enters via the nozzle as through the check valve.
I've tried adding a small filter at the rear as an experiment, but unless you block off the nozzle when sucking air in, the air would take the path of least resistance and be sucked in through the nozzle, bypassing the filter.
Just for the record, my 39-year career (now retired) in industrial process control systems (all sorts of instrumentation) involved working on a LOT of air handling systems, some parts of which were as simple as the Rocket Blower.