A rotary airlock valve has a housing having an internal horizontal taper, a mating rotor within the housing, a circular groove in each end of said rotor with a compression O-ring situated therein, a pair of compression plates within the housing, each having a circular projection adapted to contact a compression O-ring in one of the circular grooves, end plates fixed to the housing by shoulder bolts situated in and extending through the end plates, the shoulder bolts being adapted to exert compressive force on the O-rings to balance the rotor within the housing. The rotor is plastic or coated metal, the plastic rotor being utilized for lower temperature applications, i.e, ambient temperature to about 600 F., and the coated metal rotors being utilized for higher temperature (about 600 to 1200 F.) applications. There are no metal to metal moving parts. The invention can be utilized by an airlock, mass measurement feeder, control valve, or on-off valve.