What is Rotameter? Working Principl, Diagram, Construction, Advantages & Applications

In rotameter, the area of flow is measured in such a way that the head differential is constant. Hence rotameter is called variable area meter or area meter. Rotameters are widely used for metering purge flows, pump-seal fluid and coolants and lubricants for operating machinery.

Figure 1: Rotameter.

Working Principle of Rotameter

Rotameter consists of a vertical, slightly tapered, transparent tube, which consists of a plummet or float. The float is free to rise or fall in a tapered glass tube due to the variation in the flow of fluid.

Construction of Rotameter

The rotameter consists essentially of a tapered metering glass tube. Inside the tube is a float, which is the active element of the meter. The float material has a specific gravity higher than that of the fluid to be metered. The spherical slots cut into a part of the float cause it to rotate slowly about the axis of the tube and keep it centred. The stability of the float is ensured by employing a guide along which the float would slide.

Working of Rotameter

With an increase in the flow rate, the float rises in the tube and there occurs an increase in the annular area between the float and the tube. The float adjusts its position in relation to the discharge through the passes the float rides higher or lower depending on the flow rate.

Advantages of Rotameter

1. Low cost, direct indicating, minimum piping required.
2. Pressure loss in rotameter is nearly constant and small.
3. It can handle any corrosive fluid.
4. It has quite good accuracy especially at low now rates.
5. It provides linear scale.
6. It can be compensated for changes in fluid density and viscosity.
7. The capacity can be changed with relative ease by changing float, tube.
8. Condition of flow is readily visible.

Disadvantages of Rotameter

1. It must be installed in vertical position only.
2. For high pressure and temperature, it is expensive.
3. When opaque fluid is used, float may not be visible.
4. It cannot be used with liquid carrying large percentage of solids in suspension.

Applications of Rotameter

1. It is used for measurement of flow of liquid and gases.
2. The rotameters are used in large scale drug industries.
3. The rotameters are used in fermenters to control the supply of air.