They lack torque an in line fan is great to supply air from the room into the tent and is fine over a short distance, Hell even if you are venting directly out of the tent they are ok they don`t do so well with a filter on them but if there`s no duct or say half a meter of ducting they`ll work ok but compared a 5" in line on a 5" filter running over 1m of duct say 3 to 5m maybe even 10m as most "kits" come with 10m of duct right ?
Well anyway your 5" TT in line fan might be able to move 400m3 of air when its running free rig it up to a carbon filter and 10m of duct and it`s going to pull at a rate of 100 to 200m3Where as other fan types have blades with far more of an angle they are in fact an impeller type pump (like a jetski uses I guess).
Anyway they suffer far less from the drag a carbon filter and ducting add to the set upI`d take a 300m3 pump over a 400m3 in line for a carbon filter any day as that in line will lose ton`s of flow.
Hopefully that explains it without me having to get into too much detail.
Think of it like speed and torque Yes the motor driving the fan has a max speed and torque too but so does the fans design and in line fans suffer under load they are just not very good at making a vacuum Ruck and RVK make great fans When I was shopping around for new gear I found this.
http://www.ebay.co.uk/itm/350622443453?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649
I`m sure they do smaller fans too seamed the best for the money I had an in line fan on my filter as I got it cheap but a friend gave me a 6" ruck and that beat`s the shit out of any inline fan but they are like £100 good job I have nice friends lol
