Venturi Flow Meters
Venturi flow meters are a type of flow meter, which is any device used to measure the volumetric, mass, linear or nonlinear flow rate of a liquid or gas. Venturi flow meters operate according to the Venturi effect, which cites the phenomenon of fluid dynamics that is the reduction of a fluid’s pressure when it flows through a constricted pipe. To determine the flow rate of a fluid within a system, they use a differential pressure measurement. The relative ease with which venturi flow meters are operated and interpreted makes them popular for use with quite a lot of commercial and industrial applications.
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Applications of Venturi Flow Meters
The applications of flow meters are manifold, but venturi flow meters in particular are most commonly used in applications involving oil, propane and flowing water and in plumbing applications. They are also often used as the primary standard for flow calibration. Less commonly, they are used to measure the flow rate of gaseous fluids.
Design of Venturi Flow Meters
Venturi flow meters, or venturi meters, consist of a number of parts, which include a venturi tube and two pressure measurement devices. The venturi tube itself is a complex tube, made up of an entry cone, a small diameter tube and an exit cone. To generate the Venturi effect, manufacturers place the venturi tube inside a pipeline system, where it causes the diameter of the pipeline to slowly but surely decrease, until it has shrunk to the diameter of the small tube. It reaches this diameter right as the fluid arrives at and passes through the entry cone. As the fluid flows out of the small tube and into the exit cone, the pipeline is gradually restored to its original diameter. The two pressure measurement devices, or sensors, of the venturi meter are respectively located along the system before the constricted pipe and inside the small diameter tube in the venturi tube. As it operates, the venturi tube generates a quantifiable differential pressure between these two locations. In other words, when the fluid passes through this constricted tube, it is forced to decrease the pressure with which it moves. This change in pressure is known as differential pressure. The two pressure sensors measure this differential pressure. By plugging the measured pressure into a complex formula called the Bernoulli Equation, the flow meter is able to figure out the volumetric flow rate of the fluid contained within the system. In addition to the differential pressure, the exact nature of the flow rate formula also depends on: fluid viscosity, the conical angle of the venturi tube entry and exit cones, the radius of the pipeline and whether or not the fluid is compressible.
Advantages of Venturi Flow Meters
There are many other flow meters available, such as water flow meters, air flow meters, peak flow meters, ultrasonic flow meters and fuel flow meters. However, venturi meters are frequently preferred over many of these, because they boast so many advantages; venturi flow meters are praised for the superior and exceptional accuracy of their measurements, especially as compared to other flow meters. They are also marked by longevity, reliability and versatility; the former two qualities can be accredited to their lack of moving parts and the relative simplicity of their design.
The many positive attributes of venturi flow meters, such as their efficiency, durability, long operating life, versatility and accuracy, make them a worthwhile component of nearly any metering application. In addition, the fact that they do not have moving parts means that they are far less likely to need maintenance, and any maintenance they do require will be fairly straightforward.
Disadvantages of Venturi Flow Meters
Despite the many benefits they offer venturi meters do still have a few shortcomings. Mainly, they are limited because when fluid travels through the small diameter of the venturi tube, the system experiences a loss of energy. Fortunately, the venturi meter exit cone helps by recovering much of this lost energy. Manufacturers who wish to keep their venturi flow meters running as effectively and efficiently as possible must take care to note the factors that contribute to proper flow meter operation, most notably, the presence, or lack thereof, of foreign substances in the fluid. If the fluid being measured is adulterated by a foreign contaminant, the flow meter will not be able to measure flow properly. Therefore, meter and flow system operators must pay close attention to the quality of the fluids they are measuring. Also, a manufacturer would be wise to seek out a venturi meter that has been made to meet ISO quality standards. If properly monitored and maintained, a venturi flow meter will serve its operators faithfully for many years.