There are a couple of companies that specialize in rotary airlocks for feeding into high pressure systems. Several other companies have tried to make valves for this service, but I've never had any experience with them. It is a very demanding service, but the rate can be controlled within 2%-3% of a set point. The origin of the technology is in feeding coal to pressurized boilers operating at even higher pressures. In some cases I've used two in series for very high pressures. This improves the feed accuracy. An alternative that may work for the 25 psig range is a double flapper valve, but rate control is not that good. I've used these for high temperature service (over 800 F). The vent gases need to be treated with either valve. A last alternative is to use a pressurized blow tank, but this won't meter the wood dust. However, a loss-in-weight feeder could be used to feed the blow tank.