A bi-directional venturi is a type of venturi that can measure the flow rate of fluids in both directions. It is typically used in applications where the flow direction may change frequently, such as in pipelines that are used to transport both gas and liquid.

The bi-directional venturi is made up of two concentric tubes. The inner tube is the throat, and the outer tube is the venturi. The fluid flows through the inner tube, and the pressure drop is measured between the inlet and outlet of the venturi. The flow rate is then calculated using the Bernoulli equation.