Flapper Type Sight Glass Flow indicators has a hinged flapper. The flapper is deflected in the direction of flow. The angle of the flapper provides operators with an approximate gauge of flow. It operates only in one direction. This style is best applied on horizontal pipelines, but it may also be employed in vertical pipelines with upward flow.

Rotary Wheel Type Sight Glass Flow indicators have rotors or impellers that are turned by the flow of liquid or gas. Operators can observe the direction of flow and the approximate speed of flow. This indicator operates in any position (vertical, horizontal, etc.) and with any direction of flow.

Ball Type Sight Glass Flow indicator, flow moves a ball from the bottom of the indicator housing to a position at the top of the sight window. The suspension of the ball by the fluid indicates the presence of flow. This style of the indicator must be applied in vertical pipes with upward flow. Another style contains the ball inside a glass dome. When the flow diminishes, the ball drops out of view. This style must be installed in a horizontal position.

Bull Eye & Drip Tube Type Sight Glass Flow indicators designed specifically for drip observation or they may be conventional flow indicators installed with a drip tube. Drips may be observed in applications such as distillation. Normally drip indicators are used in vertical pipes having a downward flow of process fluid or (in the case of condensation) of process gas.