How Everything Works
How Everything Works How Everything Works
 

QUESTIONS AND ANSWERS
 
Question 565

How does a turbine flow meter work?
There are many different types of flow meters, some specialized to handling gases and others to handling liquids. In each case, a true flow meter transfers gas from its inlet to its outlet one unit of volume at a time and it measures how many of those volumes it transfers. There are also some flow rate meters that measure how quickly a gas or liquid is flowing. These devices normally use of turbines to measure the speed of the passing fluid and measurements from these flow rate meters can be integrated over time to determine how much gas or liquid has passed through them. However, because flow rate meters don't measure each volume of gas directly, they aren't as accurate as true flow meters.

Let me assume that you want to know about a turbine flow meter for gas. The most common of these is a device that's half filled with liquid. The "turbine" is actually a set of blades that spin in a vertical plane and spend half their times immersed in the liquid. When one of the turning blades emerges from the liquid, the empty space that appears beneath it is allowed to fill with the gas being measured. This gas flows in from the meter's inlet. Soon another blade begins to emerge from the liquid and a volume of gas is then trapped between the first blade and the second blade. Once the blades have turned almost half a turn, the first one begins to submerge again in the liquid. The gas that was trapped between it and the next blade is then squeezed out from between those blades by the liquid and flows out the meter's outlet. A geared arrangement measures how many turns the blades make and therefore how many volumes of gas have been transferred from the meter's inlet to its outlet.

         

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