What kind of air purge kit do I need for my rotary valve?

Your options are a shaft seal air purge kit, a rotor pocket air purge kit, or a combination of both. The answer is situational, but generally the shaft seal kit is best for abrasive materials, such as cement, or very fine materials that are prone to leaking. The rotor pocket option works well for ingredients that tend to pack or build up on your equipment. If your application presents a mix of both challenges, the combo air purge kit should come in handy.