feed air locks are long known a sensitive and expensive piece of machinery. even when they do work, maintenance is usually high, and jamming not infrequent. here's a bit fo summary and some new thoughts on tolerable solutions.
the usual go to solution for a feed airlock is either a rotary star valve or a double dump flap valve.
double dump valves are typically considered more forgiving and less fuel fussy, but they are very large, usually in the upwards direction, and the actuating mechanism can get complicated. you also need to control the fill into them or the top flap will get stuck, and control the stack up below, or the bottom flap won't open.
rotary valves promise more compact forms and drive, without the need to control fuel in feed, but always have the problem of fuel pinching at the entry between rotor and housing. the second main problem seems the high maintenance needed to keep the tolerances adequate for seal. some of the more interesting ones use a tapered rotor in housing so gap tolerance is an "easy" linear movement of the shaft inwards or out.
the pinching problem is most "easily" dealt with by only passing small size solids through it, and or raw power to cut the fuel. both of these routes are not attractive for feeding wood chips in small scale gasification apps.
two lesser used routes i've recently found that seem interesting-
1. controlling the feed rate to the rotary valve so the the Vs only partially fill.
usually this is done with an auger feeding the rotary valve, but other other methods are possible. either way it usually gets rid of the passive feed from the overhead hopper into the rotary valve.
here's one nice example of an auger fed rotary valve:
http://www.heizomat....llenradschleuse anyone know of more of these? and yes, know you are back to having to control the feed as in a double dump valve.
2. using an side feed rotary valve with a controllable cut to similarly prevent the full filling of the rotor V.
i only recently learned of this category of side feed star valves that try to fix the pinch through changing the fill level of the V by fill path geometry change. you can see some of these units here: http://www.carolinac...ry_airlock.html
the idea is to get the fill to the side of the rotor on the upswing. once the rotor vanes get angled up enough the material falls into the V, which is set up before the V gets to the formal housing, and thus the pinch issue at the edge is moot. no metering solution is needed at the inlet. the outlet can still have a metering/overfill problem.
either the side fill rotary or top fill rotary can have an added cut ledge that helps to control the amount of fill into the Vs of the rotor. this cut plate is set quite far above the rotor circumference so it itself does not become a binding point. angle of repose is assumed between the cut plate and rotor.
you can see an example of a side entry rotary valve with a cut plate on page 7 in the drawings in the pdf attached or at this link:
looking at these geometries, i don't see any reason we can't use a regular top to bottom rotary valve, and mount it on it sideways to the desired angle. this will achieve the same cut off and gravity fill of the V cups. to this we can then add a cut plate to further increase fuel flow happiness.
mounting a standard rotary valve on its side will complicate the hopper and reactor flanges, but potentially less so than the major cost of the more exotic side entry rotary valves. if we can use a regular star valve, there are lots of cheap sources for them, as they are commodity material handling tech around the world. whether their maintenance is tolerable is another issue.
neither will likely make a rotary valve suddenly wonderful, though it might move things towards tolerable.
anyone else have any other ideas and/or examples of interesting air tight feeding systems?