Rotameter

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is a simple industrial flow meter that measures volumetric flow of liquids and gases in a closed tube. 

they have linear scales, a relatively large measurement measurement range, low pressure drop, and are simple to install and maintain. 

are a subset of meters called variable area flow meters that measure the flow rate by allowing the fluid to travel through a tapered tube where the cross sectional area of the tube gradually becomes greater as the fluid travels through the tube.

Three basic components: a uniformly tapered flow tube a float

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measurement scale

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A control valve may be added if flow control is also desired. In operation, the rotameter is positioned vertically in the fluid system with the smallest diameter end of the tapered flow tube at the bottom. This is the  fluid inlet . The float, typically spherical, is located inside the flow tube, and is engineered so that its diameter is nearly identical to the flow tube’s inlet diameter.

The flow rate inside the rotameter is measured using a float that is lifted by the fluid flow based on the  buoyancy and velocity of the fluid opposing gravity  pulling the float down. For gasses the float responds to the velocity alone,  buoyancy is negligible. The float is always denser than the substance it is resting in and does not actually float on the substance’s surface, but rests somewhere between the substance’s surface and the bottom of the container. container.

As a liquid or gas passes through the tube, the flow causes the float to rise. As the float rises, more and more fluid flows by the float  because the tapered tube’s diameter is increasing. ltimately, a point is reached where the flow area is large enough to allow the entire volume of the fluid to flow past the float. This flow area is called the annular  passage.  passage. The float is now stationary at that level within the tube as its weight is being supported by the fluid forces which caused it to rise. This position corresponds to a point on the tube’s measurement scale and  provides an indication of the fluid’s fluid’s flow rate. The operator reads the flow from a graduated scale on the side of the rotameter.

!hanges in the flow rate cause rotameter"s float to change  position inside the tube. tube. #ince the float position position is based on gravity it is important that all rotameters be mounted vertically and oriented with the widest end of the taper taper at the top. It is also important important to remember remember that if there is no flow the float will sin$ to the bottom of the rotameter due to its own weight. %otameters can be calibrated for other fluids by understanding the basic operating principles. principles. %otameter accuracy accuracy is determined determined by the accuracy of the pressure, temperature, and flow control during the initial calibration. Any change change in the density and and weight of the float will have impacts on the rotameter"s flow reading. Additionally Additionally any changes that would affect the fluid such as pressure or temperature will also have an affect on the rotameter"s accuracy. &iven this, rotameters should be calibrated yearly to correct for any changes in the system that may have occurred.

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 'o e(ternal power required

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)ou can see the process

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%otameters are cost effective

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#imple to install and maintain

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*ow pressure drop

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%epeatability

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+ffer wide flow measurement ranges or rangeability

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ust always be installed vertically with the fluid flowing up through it

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&raduated scale will only  be valid for the specific fluid and conditions where it was calibrated.

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-ifficult to be adapted for machine reading

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%otameter"s scale is linear 

ust be made of glass or other transparent material in order for the user to see the float in the tube

ADVANTAGES

DISADVANTAGES

%otameters are used in systems that involve a liquid or gas travelling through a tube. For e(ample, rotameters are used in oil pipelines to measure the flow rate of oil as it is dispersed from one location to another across great distances. ortable rotameters can also be constructed to measure the flow rate of large bodies of liquid or gas, such as rivers, oceans, streams, as well as the atmosphere. These portable rotameters can simply be dun$ed into the substance they are measuring in order for a measurement to be ta$en.