Developing device, process cartridge, and image forming apparatus incorporating same

A developing device installable in and removable from an image forming apparatus, the developing device comprising:

• a developer bearer opposed to an image bearer of the image forming apparatus and configured to bear a developer and develop a latent image formed on a surface of the image bearer;
• a first conveyor opposed to the developer bearer, configured to convey and stir the developer in a first conveyance path;
• a second conveyor opposed to the first conveyor, configured to convey and stir the developer in a second conveyance path;
• a casing including a ceiling, configured to contain the developer, the developer bearer, the first conveyer, and the second conveyor;
• a first seal detachable from the developing device, configured to seal between the developer bearer and the first conveyor or seal a communication opening by which the first conveyance path and the second conveyance path communicate with each other;
• and
• a second seal configured to seal an opening in the ceiling above the second conveyor to form a closed space with the first seal that encloses the developer contained in the developing device,
• the second conveyor configured to be partially or entirely buried in the developer enclosed in the closed space in both of a normal posture of the developing device and an upside-down posture of the developing device to which the developing device is flipped from the normal posture, and
• a portion of the ceiling directly above at least a portion of the second conveyor declines at an angle such that a cross-sectional area of the closed space in a horizontal plane gradually increases from the ceiling of the casing toward a bottom of the developing device in the normal posture of the developing device.