In this video you can see the way a Babcock ́s QCNRV is a swing type check valve, especially designed for protection of the steam turbine systems, works.
During normal operation of the installation, the valve works as a check valve with free swinging disc, to allow the steam extraction from the system without restrictions. The valve also has a closing aid device by means of a pneumatic actuator, which shall immediately respond when a trip occurs. The valve shall close in a very short period of time to prevent the backflow of steam which might damage the turbine.
More information here.