Venturi vs Orifice
Orifice meters and Venturi meters are devices that are used to measure the pressure of flow of fluids. Both of them are differential pressure flow meters and work by placing a constriction in the flow of liquid. As fluid passes this constriction, its velocity increases according to Bernoulli Equation, which says that as elevation cannot change in a pipe, if the pressure decreases, the velocity of flowing fluid inside a pipe increases. This principle is used both in Venturi as well as orifice meters. Let us find out the differences between the two types of meters so that the reader understands their specific advantages and disadvantages and makes a choice that suits his requirements.
A Venturi meter constricts the flow of fluid and the pressure differential is measure using pressure sensors before and within the constriction. This is a very old method to measure flow rates. Orifice plate is similar in the sense that it make use of a plate with a small hole in between to place restriction in the passage of the fluid. The pressure difference before and after the orifice tells the rate of flow of the fluid. This is actually a special case of Venturi meter and cause more energy losses than Venturi meter. These orifice plates are cheap and easy to install in almost any application.
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Venturi vs Orifice • Venturi meter is expensive and takes time to install. It needs to be carefully proportioned and fabricated. On the other hand, orifice plates are easy to make, and are very cheap in comparison. They also get very easily installed in all applications. • The head lost in orifice meters is many times greater than with Venturi meters. This translates into more loss of power, which means that all the saving that accrues with cheap plates at the beginning may be offset with loss of power. Thus it is prudent to make use of orifice plates during testing period and get Venturi meters prepared to be used for real time application. • In general, orifice plates are more flexible as installing a new orifice plate for a wider or narrower opening is easier and cheaper than arranging Venturi plates. • In same conditions, the ratio of reading of Venturi meter to that of orifice plates is 1:2.58 • Orifice plates can be made of a material different that the system of piping but material of the Venturi tube must be same as that of the piping • Orifice plates are placed between flanges requiring gaskets that may leak but Venturi tubes are welded in the system and there is no question of a leakage
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