How do I know if the manual butterfly valve is open or closed?

The manual butterfly valve uses the handle to twist the disc plate, so that the disc plate and the center line of the valve body channel are coincident or vertical, so as to realize the function of fully opening or fully closing the pipeline.

First observe the angular relationship between the handle and the centerline of the valve body pipeline;

As shown in the figure below: the handle is perpendicular to the centerline of the valve body pipeline, indicating that the manual butterfly valve is in a fully closed state.
Conversely, if the handle coincides with the centerline of the valve body line, the manual butterfly valve is fully open.

Opening status:
As shown in the figure below: the handle and the center line of the valve body are at different angles, indicating that the manual butterfly valve is in a transitional state of opening and closing. According to the above number, the opening degree of the valve is controlled. The larger the number, the greater the opening degree.