Rotameter Type Flow Meter – Description

A Rotameter is a type of variable-area flow meter used to measure the flow rate of liquids and gases in a vertical pipeline.

Construction

A rotameter consists of:

• A vertically mounted tapered tube (wider at the top than at the bottom).
• A float (or bob) placed inside the tube.
• A calibrated scale marked along the tube to indicate flow rate.

Working Principle

When fluid enters from the bottom of the tube:

1. The fluid flows upward and exerts an upward force on the float.
2. The float rises until the upward force caused by fluid flow balances the downward force due to the float’s weight.
3. As flow rate increases, the float moves higher in the tapered tube, increasing the annular area available for flow.
4. The float position corresponds to a specific flow rate, which is read directly from the scale.

Principle of Operation

The rotameter operates on the principle of variable flow area with nearly constant pressure drop across the float.

Advantages

• Simple construction and operation.
• Direct reading of flow rate.
• No external power required.
• Low pressure loss.
• Suitable for a wide range of liquids and gases.

Disadvantages

• Must be installed vertically.
• Accuracy can be affected by fluid density and viscosity.
• Glass tubes are fragile (though metal-tube designs are available).

Applications

• Water treatment plants.
• Chemical and pharmaceutical industries.
• Laboratory flow measurement.
• Gas flow monitoring systems.
• Process control industries.

Diagram (Simplified)

     Wider End
        ↑
      ┌─────┐
      │  ○  │ ← Float
      │     │
      │     │
      │     │
      └─────┘
        ↑
      Fluid In
    (Narrow End)

A rotameter is widely used because it provides a simple, reliable, and economical method of measuring fluid flow rates in industrial and laboratory applications.