How Do Flow Meters Work?
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Variable Area Flow Meter
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The variable area flow meter is used to measure the flow of liquids and gases by the force of gravity and pressure. It consists of a tapered cylinder that is larger at the top than it is at the bottom. In the cylinder is a float that has buoyancy and floats on the water. As pressure increases, the force pushes the float upwards in the cylinder and a reading can be made using a line gauge. The cylinder expands at the top to account for the change in pressure that must be attained to make the float rise. This is why it is called a variable area flow meter.
Slotted Tube Flow Meters
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Another common flow meter is the slotted tube flow meter. It consists of a straight cylinder and piston. The pressure will cause the piston to rise in the cylinder and give a pressure reading. These use a clear viewing tube which allows an engineer to read the level of the piston, as the piston is contained in an enclosed tube. The whole unit is "T" shaped with a disc that contacts and reacts to the flow of liquids through the system. This then pushes on the piston in the cylinder.
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More Flow Meters
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There are dozens more flow meters for a variety of uses. There are electromagnetic flow meters that use Faraday's law of magnetic induction to measure flow, Coriolis flow meters that use rotation, and turbine flow meters, which use turbine blades inside of a pipe to measure the amount of fluid passing through them. There are even flow meters that use ultrasonic waves to measure fluid flow, as in the Doppler flow meter.
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