venturi tube

a device for measuring the flow of a fluid, consisting of a tube with a short, narrow center section and widened, tapered ends, so that a fluid flowing through the center section at a higher velocity than through an end section creates a pressure differential that is a measure of the flow of the fluid.

physics a device for measuring fluid flow, consisting of a tube so constricted that the pressure differential produced by fluid flowing through the constriction gives a measure of the rate of flow

Also called: venturi a tube with a constriction used to reduce or control fluid flow, as one in the air inlet of a carburettor