Rotameters are used to measure the flow rate of a gas through an orifice or series of tubing. There are many different types of rotameters available on the market today; most of them work based on gravity. The gas flow causes a small ball to rise in a graduated column, while gravity pushes down. This results in an accurate measure of flow rate, generally measured in liters per minute. Most rotameters are also equipped with a dial in order to set the flow at a desired rate. Reading a rotameter from the top is fairly simple.
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Set up the rotameter on a flat surface. It is important for the meter to be level. You may need to use clamps to attach the rotameter to something sturdy; some are too large to stand on their own.
Connect the gas source through tubing to the rotameter and turn on the gas. Some rotameters come with standard fittings for various size tubing. You may need to purchase tubing connections from a hardware store.
Find the ball floating in the middle of the rotameter column. Look at the bottom of the ball, and see where it lines up with the scale on the side of the meter. This is the flow rate. Rotameters are marked from the top to bottom, increasing to decreasing flow, similar to a thermometer. The scale will vary based on the make of the rotameter.