This RFMP having both ends open for air intake, while the whole body is surrounded by net.
Then this incoming air will come out from the net. Any dust in this air with size bigger than the net density will be blocked by the net, leaving filtered air come out.
Let say the net surface facing the RFMP body we called it inner surface of net, while the net surface facing out of this RFMP body we called it outer surface of net. Then most the dust will trap on the inner surface of net.
Over time when most of the inner surface of net been clogged by the dust, then the user needs to take out this RFMP for cleaning.
This RFMP can be cleaned easily by water spray to the side of this RFMP, with this RFMP hold in vertical position as shown in Fig. 2 below. .