A very common application we sell knife gate valves for is on the bottom of cement hoppers (dry powder). There are a few recommendations we make, some more critical than others.
1. Use a uni directional knife gate valve. Here one side is slightly smaller (reduced bore) so it protects the seat and does not compact powder into the seat as it lets it fall away on one side.
2. Metal to metal seat is preferable
3. Consider a cone deflector. This further enhances protection to your seat but is not critical. We have many customers that use knife gate valves on hoppers without this but it does increase longevity especially if the usage is high.
4. Do not use a bi directional flow knife gate valve on this application.
An example of such a knife gate valve can be found here.