DP (Differential Pressure) flowmeter works based on a pressure measurement on both sides of a mechanical resistance or obstacle (flow element) in the fluid streamline. It is the simplest flowmeter we can find in industries. 

Flow rate is a function of measured DP's root multiple in a K-factor calculated by the flow element manufacturer.  The well-known device of this flowmeter type is the orifice plate.  

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The pressure that comes out from both sides of flowmeters will be conveyed to differential pressure gauges legs for local indication or transmitter legs for connecting to the control system. 

Averaging Pitot tubes and venturi tubes are another type of flowmeter. 

Sometimes, instead of measuring the pressure difference before and after a fixed flow element, the measurement between static pressure and dynamic pressure is used. We have this rule in V-Cone, Pitot tube, and averaging Pitot tube. 

Metron is the biggest and most famous manufacturer of flow elements in Italy. 

You are invited to have a tour of our factory.