Rotameter: A rotameter is a device thatmeasures the flow rate of liquid or gasin a closed tube. A rotameter consists of aConical Tube, typically made of glasswith a float, actually a shapedweight, inside that is pushed up by theDrag Force of the flow and pulleddown by Gravity. The position of thefloat indicates the flow rate on amarked scale.
Working of Rotameter: A rotameter is basically constructed of a verticallyoriented glass tapered tube and a metering float which is freeto move within the tube. When there is no fluid flow, the floatrests freely at the bottom of the tube. When liquid enters thebottom of the tube, the metering float begins to rise. The position of the float changes directly with the flowrate. The accurate position of the float is at the point where thedifferential pressure between the upper and lower surfacesbalances the weight of the float. The greater the flow, thehigher the float gets lifted.
Advantages:•A rotameter requires no external power or fuel, it uses only the inherent properties of the fluid, along with gravity, to measure flow rate.•A rotameter is also a relatively simple device that can be mass manufactured out of cheap materials, allowing for its widespread use.•Since the area of the flow passage increases as the float moves up the tube, the scale is approximately linear.
Railway rotameterThe New South Wales Government Railways constructed in 1903 adevice for measuring the length of its lines of railway. That authoritynamed the machine a Rotameter. It consisted of a four-wheel trolleywith an additional large fifth wheel which traveled along therunning surface of the rail. Its last recorded use was in the 1920s.