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How to stir wood-chips

(Click to enlarge photo)

Wood-pellets are generally no problem at all and flow rather like a liquid does. Wood-chips, however, have one or two bad habits and can cause serious difficulties for the unwary. First of all they don't flow easily so there is no reliability in just filling a hopper above an auger as, sometimes it will work and sometimes it won't. There needs to be some means of agitating the wood-chips to persuade them to make the downward journey. This is all due to a behaviour called "bridging". As the name suggests the wood-chips can form an arch where nothing above can then fall down to the auger. Another annoying feature is that wood-chips tend to become more compact over time. A hopper that was filled in the morning and would have worked fine then may not empty so easily at a later time.

My solution to the above is something I call a stirrer. Its actually a small mains motor driving a wheel-chair gearbox that rotates a vertical tube in the centre of the hopper, the end of which sits about an inch above the auger. In addition, there are chains attached to the top of the vertical tube that swing out as it rotates. The idea is that the chains gradually undermine the wood-chips and prevent them from bridging or loosen them sufficiently enough to fall if they are compacted. I made a simple three-way support for the arrangement to sit on top of the hopper. It can easily be removed for maintenance although wood-chips or pellets can be poured-in with it remaining in place. The stirrer motor does not have to be powered all of the time, I found that a couple of revolutions and then a pause for a minute was about right. The vertical shaft turns at around 100rpm.