The orifice plate narrows the cross-section in the tube. The constriction of the cross-section causes an increase in velocity which results in a measurable decrease in pressure. Taking the orifice geometry into account, the flow rate can be calculated from the decrease in pressure using Bernoulli’s principle and the Continuity law.
The necessary connections are provided for measurement and display of the pressure loss on manometer. The transparent front makes the measuring orifice visible, thus aiding understanding of the operating principle.