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Measuring Principle of Differential Pressure Flow
Jan 22, 2021

About 300 years ago, the Swiss mathematician and physicist Bernoulli discovered the direct relationship between the pressure and the flow velocity of the fluid in the pipeline. The Italian physicist Venturi also conducted related flow research and made the first application of DP flow meter for closed pipeline in 1979.


The differential pressure flowmeter is designed with a human intervention structure in the measuring tube. Taking the orifice plate as an example, there is a pressure tapping hole in the front and back of the orifice plate on the pipe line, and two pulse lines connect the HP and LP diaphragm side of the differential pressure sensor. The two independent pressure chambers separated by diaphragm, the slight differential pressure can be accurately measured.


When fluid remains stable, the pressure before and after the orifice is the same in the pipe line.


When fluid start to flow, the velocity after orifice plate increases significantly because the cross-section of the pipe is throttled by the orifice plate. According to the principle of fluidics, the static pressure at this point drops, so different pressure will be detected by the pressure transmitter. The pressure in front of the orifice is larger, and the pressure behind the orifice is smaller. The differential pressure is proportional to the flow rate which the mass and volume flow of the fluid can be calculated out.


The bigger of pressure drop, the greater the pressure difference would be measured.


Orifice plate can meet most measurement needs In variety industrial applications, but there are some other designs for specific measurement tasks to overcome external influences, such as excessive pressure loss or component wear caused by solids in the fluid. Sudden flow restriction will cause severe surging of the fluid, needs a circular nozzle and the funnel-shaped inlet can significantly reduce the surging, thereby reducing the pressure loss. Therefore, the nozzle is particularly suitable for higher flow rates or fluid with solid particles.


The venturi flow meter nozzle reduces the surge flow to a greater extent, mainly because a longer conical pipe structure is used in the pipeline for throttling, which can optimize the pressure loss and differential pressure of the process.


Differential pressure flowmeter has been used for the measurement of industrial flow for more than 100 years globally. It's suitable for the measurement of liquid, gas or steam, and also suitable for extreme high temperature and high pressure conditions.