Sentry C-21 casing hangers are the non-automatic solution for hanging casing. The split bowl utilizes the same upper slip segments as the C-22 and C-29 hangers and incorporates a separate seal assembly. This has two benefits. It prevents any well or test pressure from adding to the radial compression of the slip segments. And it is a primary casing seal that can be replaced during workover operations without picking up the pipe.
Non Automatic casing hangers are typically used when the casing string weight is not sufficient enough to energize the seal mechanism in automatic casing hangers
The Type-H seal ring utilizes S (OD) and CS (ID) seals to provide the primary seal on the string of casing being suspended in the casing hanger
The C-21 casing hanger seal mechanism cannot be used if LDS are present in the upper flange of the casing head