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Wastewater
Treatment Articles Index
When you drive your car and the speedometer reads 60 miles per hour, how do you know it is correct? You don't, really. However, it doesn't affect you because most speedometers are highly reliable and consistent.
If you did want to check the accuracy of your speedometer, you could use those mile markers that you see along the expressways. You could drive at 60 miles per hour and see if it takes you a minute to pass from one mile marker to the next. In other words, you can check the accuracy of the instrument without the use of special equipment. You can check the speedometer reading by observing the mile markers and using a watch.
Two types of flow meters allow you to check the reading with a simple physical observation: the parshall flume and the venturi meter.
The parshall flume is an open channel flow meter. The depth of water in the flume is directly related to the flow. For each water depth measurement, there is a corresponding flow reading. In other words, if you measure the water depth at 7 inches with a ruler, you know that the flow is 400 gallons per minute.
The venturi meter is similar except that it is used in pressure pipe. In this case, the physical measurement is pressure in psi or pounds per square inch. A pressure gage is a simple device.
These types of flow meters may provide some small measure of comfort in cases where the flow readings are used for billing purposes and lots of money is involved. You are not completely at the mercy of the instrument technician.
Wastewater Treatment Articles Index
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