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# What is a Tube Flow Meter?

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• Written By: Jean Marie Asta
• Edited By: Jessica Seminara
2003-2017
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A tube flow meter measures the pressure of the flow of either liquids or gasses through a tube or pipe. These meters are used in industrial settings to make sure that various devices are receiving a proper amount and pressure of various fluids. There are many different kinds of flow meters. The most common types will be discussed here.

Using an open channel flow meter is the most common and easiest way to measure the flow of nonhazardous liquids. As liquids spill out of a tube, the distance they shoot out into a receptacle can be used to determine the amount of pressure in the tube. These measurements can be used to adjust the pressure of the liquid. If the fluid that a person wishes to measure is in a gas form, however, or if exposure to air causes it to convert into a gas or another element, then these meters are inaccurate and another method will have to be used.

Orifice plates can solve this problem. Another form of tube flow meter, an orifice plate uses a small disk with a hole in it to restrict the flow of a fluid through a tube. This causes a pressure buildup right before the area in the pipe where the plate is installed. A device measures the pressure here and a short distance after the plate where the fluidâ€™s pressure is decreased and uses these two numbers to determine the pressure within the tube.

Using an orifice plate is an accurate form of measurement, but the device itself can cause the pressure to be changed slightly. If slight changes affect the purpose of the measurement, a Venturi tube flow meter can provide a more accurate idea of the pressure in a tube without affecting the pressure as much. These meters do this by creating a bottleneck that is not as small as the hole in the orifice plate and is longer so pressure stays more constant. Pressure is measured before this bottleneck and at the narrowest point for optimal results.

A flow nozzle is similar to a Venturi tube flow meter. It is inserted into a tube and measures pressure from the middle of the bottleneck and before it. Flow nozzles are, however, not as large or as sensitive as Venturi tubes.

The pitot tube is a type of tube flow meter that is used mainly for measuring gas pressure. It consists of a tube that is placed within the pipe where the gas flows. Holes on one side of the tube face into the flow of the gas, while those on the other side face in the opposite direction. The difference in pressure from these sets of holes is used to calculate the rate of gas flow.

These are just the basic tube flow meters used for science and industrial purposes. There are more complex forms. Most of them rely on the principle of creating a small alteration to the pressure in order to determine how strong it is.